M M F M F M M M
F M F F M M
M M M F M
F F F F
M M M
F M
These examples are more than sufficient. It is quite evident that the distribution of the sexes is not governed by any rule. All that I can say on consulting the whole of my notes, which contain a good many instances of complete layings–most of them, unfortunately, spoilt through gaps caused by parasites, the death of the larva, the failure of the egg to hatch and other accidents–all that I can say in general is that the complete series begins with females and nearly always ends with males. The incomplete series can teach us nothing in this respect, for they are only fragments starting we know not whence; and it is impossible to tell whether they should be ascribed to the beginning, to the end, or to an intermediate period of the laying. To sum up: in the laying of the Three-pronged Osmia, no order governs the succession of the sexes; only, the series has a marked tendency to begin with females and to finish with males.
The brambles, in my district, harbour two other Osmiae, both of much smaller size: O. detrita, PEREZ, and O. parvula, DUF. The first is very common, the second very rare; and until now I have found only one of her nests, placed above a nest of O. detrita, in the same bramble. Here, instead of the lack of order in the distribution of the sexes which we find with O. tridentata, we have an order remarkable for consistency and simplicity. I have before me the list of the series of O. detrita collected last winter. Here are some of them:
1. A series of twelve: seven females, beginning with the bottom of the tunnel, and then five males.
2. A series of nine: three females first, then six males.
3. A series of eight: five females followed by three males.
4. A series of eight: seven females followed by one male.
5. A series of eight: one female followed by seven males.
6. A series of seven: six females followed by one male.
The first series might very well be complete. The second and fifth appear to be the end of layings, of which the beginning has taken place elsewhere, in another bramble-stump. The males predominate and finish off the series. Nos. 3, 4 and 6, on the other hand, look like the beginnings of layings: the females predominate and are at the head of the series. Even if these interpretations should be open to doubt, one result at least is certain: with O. detrita, the laying is divided into two groups, with no intermingling of the sexes; the first group laid yields nothing but females, the second, or more recent, yields nothing but males.
What was only a sort of attempt with the Three-pronged Osmia–who, it is true, begins with females and ends with males, but muddles up the order and mixes the two sexes anyhow between the extreme points– becomes a regular law with her kinswoman. The mother occupies herself at the start with the stronger sex, the more necessary, the better- gifted, the female sex, to which she devotes the first flush of her laying and the fullness of her vigour; later, when she is perhaps already at the end of her strength, she bestows what remains of her maternal solicitude upon the weaker sex, the less-gifted, almost negligible male sex.
O. parvula, of whom I unfortunately possess but one series, repeats what the previous witness has just shown us. This series, one of nine cocoons, comprises five females followed by four males, without any mixing of the sexes.
Next to these disgorgers of honey and gleaners of pollen-dust, it would be well to consult other Hymenoptera, Wasps who devote themselves to the chase and pile their cells one after the other, in a row, showing the relative age of the cocoons. The brambles house several of these: Solenius vagus, who stores up Flies; Psen atratus, who provides her grubs with a heap of Plant-lice; Trypoxylon figulus, who feeds them with Spiders.
Solenius vagus digs her gallery in a bramble-stick that is lopped short, but still fresh and green. The house of this Fly-huntress, therefore, suffers from damp, as the sap enters, especially on the lower floors. This seems to me rather insanitary. To avoid the humidity, or for other reasons which escape me, the Solenius does not dig very far into her bramble-stump and consequently can stack but a small number of cells in it. A series of five cocoons gives me first four females and then one male; another series, also of five, contains first three females, with two males following. These are the most complete that I have for the moment.
I reckoned on the Black Psen, or Psen atratus, whose series are pretty long; it is a pity that they are nearly always greatly interfered with by a parasite called Ephialtes mediator. (Cf. “The Life of the Fly”: chapter 2.–Translator’s Note.) I obtained only three series free from gaps: one of eight cocoons, comprising only females; one of six, likewise consisting wholly of females; lastly, one of eight, formed exclusively of males. These instances seem to show that the Psen arranges her laying in a succession of females and a succession of males; but they tell us nothing of the relative order of the two series.
>From the Spider-huntress, Trypoxylon figulus, I learnt nothing decisive. She appeared to me to rove about from one bramble to the next, utilizing galleries which she has not dug herself. Not troubling to be economical with a lodging which it has cost her nothing to acquire, she carelessly builds a few partitions at very unequal heights, stuffs three or four compartments with Spiders and passes on to another bramble-stump, with no reason, so far as I know, for abandoning the first. Her cells, therefore, occur in series that are too short to give us any useful information.
This is all that the bramble-dwellers have to tell us; I have enumerated the list of the principal ones in my district. We will now look into some other Bees who arrange their cocoons in single files: the Megachiles (Cf. Chapter 8 of the present volume.–Translator’s Note.), who cut disks out of leaves and fashion the disks into thimble-shaped receptacles; the Anthidia (Cf. Chapters 9 and 10 of the present volume.–Translator’s Note.), who weave their honey- wallets out of cotton-wool and arrange their cells one after the other in some cylindrical gallery. In most cases, the home is the produce of neither the one nor the other. A tunnel in the upright, earthy banks, the old work of some Anthophora, is the usual dwelling. There is no great depth to these retreats; and all my searches, zealously prosecuted during a number of winters, procured me only series containing a small number of cocoons, four or five at most, often one alone. And, what is quite as serious, nearly all these series are spoilt by parasites and allow me to draw no well-founded deductions.
I remembered finding, at rare intervals, nests of both the Anthidium and the Megachile in the hollows of cut reeds. I thereupon installed some hives of a new kind on the sunniest walls of my enclosure. They consisted of stumps of the great reed of the south, open at one end, closed at the other by the natural knot and gathered into a sort of enormous pan-pipe, such as Polyphemus might have employed. The invitation was accepted: Osmiae, Anthidia and Megachiles came in fairly large numbers, especially the first, to benefit by the queer installation.
In this way I obtained some magnificent series of Anthidia and Megachiles, running up to a dozen. There was a melancholy side to this success. All my series, with not one exception, were ravaged by parasites. Those of the Megachile (M. sericans, FONSCOL), who fashions her goblets with robinia-, holm-, and terebinth-leaves, were inhabited by Coelioxys octodentata (A Parasitic Bee.–Translator’s Note.); those of the Anthidium (A. florentinum, LATR.) were occupied by a Leucopsis. Both kinds were swarming with a colony of pigmy parasites whose name I have not yet been able to discover. In short, my pan-pipe hives, though very useful to me from other points of view, taught me nothing about the order of the sexes among the Leaf- cutters and the cotton-weavers.
I was more fortunate with three Osmiae (O. tricornis, LATR., O. cornuta, LATR., and O. Latreillii, SPIN.), all of whom gave me splendid results, with reed-stumps arranged either against the walls of my garden, as I have just said, or near their customary abode, the huge nests of the Mason-bee of the Sheds. One of them, the Three- horned Osmia, did better still: as I have described, she built her nests in my study, as plentifully as I could wish, using reeds, glass tubes and other retreats of my selecting for her galleries.
We will consult this last, who has furnished me with documents beyond my fondest hopes, and begin by asking her of how many eggs her average laying consists. Of the whole heap of colonized tubes in my study, or else out of doors, in the hurdle-reeds and the pan-pipe appliances, the best-filled contains fifteen cells, with a free space above the series, a space showing that the laying is ended, for, if the mother had any more eggs available, she would have lodged them in the room which she leaves unoccupied. This string of fifteen appears to be rare; it was the only one that I found. My attempts at indoor rearing, pursued during two years with glass tubes or reeds, taught me that the Three-horned Osmia is not much addicted to long series. As though to decrease the difficulties of the coming deliverance, she prefers short galleries, in which only a part of the laying is stacked. We must then follow the same mother in her migration from one dwelling to the next if we would obtain a complete census of her family. A spot of colour, dropped on the Bee’s thorax with a paint- brush while she is absorbed in closing up the mouth of the tunnel, enables us to recognize the Osmia in her various homes.
In this way, the swarm that resided in my study furnished me, in the first year, with an average of twelve cells. Next year, the summer appeared to be more favourable and the average became rather higher, reaching fifteen. The most numerous laying performed under my eyes, not in a tube, but in a succession of Snail-shells, reached the figure of twenty-six. On the other hand, layings of between eight and ten are not uncommon. Lastly, taking all my records together, the result is that the family of the Osmia fluctuates round about fifteen in number.
I have already spoken of the great differences in size apparent in the cells of one and the same series. The partitions, at first widely spaced, draw gradually nearer to one another as they come closer to the aperture, which implies roomy cells at the back and narrow cells in front. The contents of these compartments are no less uneven between one portion and another of the string. Without any exception known to me, the large cells, those with which the series starts, have more abundant provisions than the straitened cells with which the series ends. The heap of honey and pollen in the first is twice or even thrice as large as that in the second. In the last cells, the most recent in date, the victuals are but a pinch of pollen, so niggardly in amount that we wonder what will become of the larva with that meagre ration.
One would think that the Osmia, when nearing the end of the laying, attaches no importance to her last-born, to whom she doles out space and food so sparingly. The first-born receive the benefit of her early enthusiasm: theirs is the well-spread table, theirs the spacious apartments. The work has begun to pall by the time that the last eggs are laid; and the last-comers have to put up with a scurvy portion of food and a tiny corner.
The difference shows itself in another way after the cocoons are spun. The large cells, those at the back, receive the bulky cocoons; the small ones, those in front, have cocoons only a half or a third as big. Before opening them and ascertaining the sex of the Osmia inside, let us wait for the transformation into the perfect insect, which will take place towards the end of summer. If impatience gets the better of us, we can open them at the end of July or in August. The insect is then in the nymphal stage; and it is easy, under this form, to distinguish the two sexes by the length of the antennae, which are larger in the males, and by the glassy protuberances on the forehead, the sign of the future armour of the females. Well, the small cocoons, those in the narrow front cells, with their scanty store of provisions, all belong to males; the big cocoons, those in the spacious and well-stocked cells at the back, all belong to females.
The conclusion is definite: the laying of the Three-horned Osmia consists of two distinct groups, first a group of females and then a group of males.
With my pan-pipe apparatus displayed on the walls of my enclosure and with old hurdle-reeds left lying flat out of doors, I obtained the Horned Osmia in fair quantities. I persuaded Latreille’s Osmia to build her nest in reeds, which she did with a zeal which I was far from expecting. All that I had to do was to lay some reed-stumps horizontally within her reach, in the immediate neighbourhood of her usual haunts, namely, the nests of the Mason-bee of the Sheds. Lastly, I succeeded without difficulty in making her build her nests in the privacy of my study, with glass tubes for a house. The result surpassed my hopes.
With both these Osmiae, the division of the gallery is the same as with the Three-horned Osmia. At the back are large cells with plentiful provisions and widely-spaced partitions; in front, small cells, with scanty provisions and partitions close together. Also, the larger cells supplied me with big cocoons and females; the smaller cells gave me little cocoons and males. The conclusion therefore is exactly the same in the case of all three Osmiae.
Before dismissing the Osmiae, let us devote a moment to their cocoons, a comparison of which, in the matter of bulk, will furnish us with fairly accurate evidence as to the relative size of the two sexes, for the thing contained, the perfect insect, is evidently proportionate to the silken wrapper in which it is enclosed. These cocoons are oval-shaped and may be regarded as ellipsoids formed by a revolution around the major axis. The volume of one of these solids is expressed in the following formula:
4 / 3 x pi x a x (b squared),
in which 2a is the major axis and 2b the minor axis.
Now, the average dimensions of the cocoons of the Three-horned Osmia are as follows:
2a = 13 mm. (.507 inch.–Translator’s Note.), 2b = 7 mm. (.273 inch.- -Translator’s Note.) in the females;
2a = 9 mm. (.351 inch.–Translator’s Note.), 2b = 5 mm. (.195 inch.– Translator’s Note.) in the males.
The ratio therefore between 13 x 7 x 7 = 637 and 9 x 5 x 5 = 225 will be more or less the ratio between the sizes of the two sexes. This ratio is somewhere between 2 to 1 and 3 to 1. The females therefore are two or three times larger than the males, a proportion already suggested by a comparison of the mass of provisions, estimated simply by the eye.
The Horned Osmia gives us the following average dimensions:
2a = 15 mm. (.585 inch.–Translator’s Note.), 2b = 9 mm. (.351 inch.- -Translator’s Note.) in the females;
2a = 12 mm. (.468 inch.–Translator’s Note.), 2b = 7 mm. (.273 inch.- -Translator’s Note.) in the males.
Once again, the ratio between 15 x 9 x 9 = 1215 and 12 x 7 x 7 = 588 lies between 2 to 1 and 3 to 1.
Besides the Bees who arrange their laying in a row, I have consulted others whose cells are grouped in a way that makes it possible to ascertain the relative order of the two sexes, though not quite so precisely. One of these is the Mason-bee of the Walls. I need not describe again her dome-shaped nest, built on a pebble, which is now so well-known to us. (Cf. “The Mason-bees”: chapter 1.–Translator’s Note.)
Each mother chooses her stone and works on it in solitude. She is an ungracious landowner and guards her site jealously, driving away any Mason who even looks as though she might alight on it. The inhabitants of the same nest are therefore always brothers and sisters; they are the family of one mother.
Moreover, if the stone presents a large enough surface–a condition easily fulfilled–the Mason-bee has no reason to leave the support on which she began her laying and go in search of another whereon to deposit the rest of her eggs. She is too thrifty of her time and of her mortar to involve herself in such expenditure except for grave reasons. Consequently, each nest, at least when it is new, when the Bee herself has laid the first foundations, contains the entire laying. It is a different thing when an old nest is restored and made into a place for depositing the eggs. I shall come back later to such houses.
A newly-built nest then, with rare exceptions, contains the entire laying of one female. Count the cells and we shall have the total list of the family. Their maximum number fluctuates round about fifteen. The most luxuriant series will occasionally reach as many as eighteen, though these are very scarce.
When the surface of the stone is regular all around the site of the first cell, when the mason can add to her building with the same facility in every direction, it is obvious that the groups of cells, when finished, will have the oldest in the central portion and the more recent in the surrounding portion. Because of this juxtaposition of the cells, which serve partly as a wall to those which come next, it is possible to form some estimate of the chronological order of the cells in the Chalicodoma’s nest and thus to discover the sequence of the two sexes.
In winter, by which time the Bee has long been in the perfect state, I collect Chalicodoma-nests, removing them bodily from their support with a few smart sideward taps of the hammer on the pebbles. At the base of the mortar dome the cells are wide agape and display their contents. I take the cocoon from its box, open it and take note of the sex of the insect enclosed.
I should probably be accused of exaggeration if I mentioned the total number of the nests which I have gathered and the cells which I have inspected by this method during the last six or seven years. I will content myself with saying that the harvest of a single morning sometimes consisted of as many as sixty nests of the Mason-bee. I had to have help in carrying home my spoils, even though the nests were removed from their stones on the spot.
>From the enormous number of nests which I have examined, I am able to state that, when the cluster is regular, the female cells occupy the centre and the male cells the edges. Where the irregularity of the pebble has prevented an even distribution around the initial point, the same rule has been observed. A male cell is never surrounded on every side by female cells: either it occupies the edges of the nest, or else it adjoins, at least on some sides, other male cells, of which the last form part of the exterior of the cluster. As the surrounding cells are obviously of a later date than the inner cells, it follows that the Mason-bee acts like the Osmiae: she begins her laying with females and ends it with males, each of the sexes forming a series of its own, independent of the other.
Some further circumstances add their testimony to that of the surrounded and surrounding cells. When the pebble projects sharply and forms a sort of dihedral angle, one of whose faces is more or less vertical and the other horizontal, this angle is a favourite site with the Mason, who thus finds greater stability for her edifice in the support given her by the double plane. These sites appear to me to be in great request with the Chalicodoma, considering the number of nests which I find thus doubly supported. In nests of this kind, all the cells, as usual, have their foundations fixed to the horizontal surface; but the first row, the row of cells first built, stands with its back against the vertical surface.
Well, these older cells, which occupy the actual edge of the dihedral angle, are always female, with the exception of those at either end of the row, which, as they belong to the outside, may be male cells. In front of this first row come others. The female cells occupy the middle portion and the male the ends. Finally, the last row, closing in the remainder, contains only male cells. The progress of the work is very visible here: the Mason has begun by attending to the central group of female cells, the first row of which occupies the dihedral angle, and has finished her task by distributing the male cells round the outside.
If the perpendicular face of the dihedral angle be high enough, it sometimes happens that a second row of cells is placed above the first row backing on to that plane; a third row occurs less often. The nest is then one of several storeys. The lower storeys, the older, contain only females; the upper, the more recent storey, contains none but males. It goes without saying that the surface layer, even of the lower storeys, can contain males without invalidating the rule, for this layer may always be looked upon as the Chalicodoma’s last work.
Everything therefore contributes to show that, in the Mason-bee, the females take the lead in the order of primogeniture. Theirs is the central and best-protected part of the clay fortress; the outer part, that most exposed to the inclemencies of the weather and to accidents, is for the males.
The males’ cells do not differ from the females’ only by being placed at the outside of the cluster; they differ also in their capacity, which is much smaller. To estimate the respective capacities of the two sorts of cells, I go to work as follows: I fill the empty cell with very fine sand and pour this sand back into a glass tube measuring 5 millimetres (.195 inch.–Translator’s Note.) in diameter. >From the height of the column of sand we can estimate the comparative capacity of the two kinds of cells. I will take one at random among my numerous examples of cells thus gauged.
It comprises thirteen cells and occupies a dihedral angle. The female cells give me the following figures, in millimetres, as the height of the columns of sand:
40, 44, 43, 48, 48, 46, 47
(1.56, 1.71, 1.67, 1.87, 1.87, 1.79, 1.83 inches.–Translator’s Note.),
averaging 45. (1.75 inches.–Translator’s Note.)
The male cells give me:
32, 35, 28, 30, 30, 31
(1.24, 1.36, 1.09, 1.17, 1.17, 1.21 inches.–Translator’s Note.),
averaging 31. (1.21 inches.–Translator’s Note.)
The ratio of the capacity of the cells for the two sexes is therefore roughly a ratio of 4 to 3. The actual contents of the cell being proportionate to its capacity, the above ratio must also be more or less the ratio of provisions and sizes between females and males. These figures will assist us presently to tell whether an old cell, occupied for a second or third time, belonged originally to a female or a male.
The Chalicodoma of the Sheds cannot give us any information on this matter. She builds under the same eaves, in excessively populous colonies; and it is impossible to follow the labours of any single Mason, whose cells, distributed here and there, are soon covered up with the work of her neighbours. All is muddle and confusion in the individual output of the swarming throng.
I have not watched the work of the Chalicodoma of the Shrubs with close enough attention to be able to state definitely that this Bee is a solitary builder. Her nest is a ball of clay hanging from a bough. Sometimes, this nest is the size of a large walnut and then appears to be the work of one alone; sometimes, it is the size of a man’s fist, in which case I have no doubt that it is the work of several. Those bulky nests, comprising more than fifty cells, can tell us nothing exact, as a number of workers must certainly have collaborated to produce them.
The walnut-sized nests are more trustworthy, for everything seems to indicate that they were built by a single Bee. Here females are found in the centre of the group and males at the circumference, in somewhat smaller cells, thus repeating what the Mason-bee of the Pebbles has told us.
One clear and simple rule stands out from this collection of facts. Apart from the strange exception of the Three-pronged Osmia, who mixes the sexes without any order, the Bees whom I studied and probably a crowd of others produce first a continuous series of females and then a continuous series of males, the latter with less provisions and smaller cells. This distribution of the sexes agrees with what we have long known of the Hive-bee, who begins her laying with a long sequence of workers, or sterile females, and ends it with a long sequence of males. The analogy continues down to the capacity of the cells and the quantities of provisions. The real females, the Queen-bees, have wax cells incomparably more spacious than the cells of the males and receive a much larger amount of food. Everything therefore demonstrates that we are here in the presence of a general rule.
But does this rule express the whole truth? Is there nothing beyond a laying in two series? Are the Osmiae, the Chalicodomae and the rest of them fatally bound by this distribution of the sexes into two distinct groups, the male group following upon the female group, without any mixing of the two? Is the mother absolutely powerless to make a change in this arrangement, should circumstances require it?
The Three-pronged Osmia already shows us that the problem is far from being solved. In the same bramble-stump, the two sexes occur very irregularly, as though at random. Why this mixture in the series of cocoons of a Bee closely related to the Horned Osmia and the Three- horned Osmia, who stack theirs methodically by separate sexes in the hollow of a reed? What the Bee of the brambles does cannot her kinswomen of the reeds do too? Nothing, so far as I know, can explain this difference in a physiological act of primary importance. The three Bees belong to the same genus; they resemble one another in general outline, internal structure and habits; and, with this close similarity, we suddenly find a strange dissimilarity.
There is just one thing that might possibly arouse a suspicion of the cause of this irregularity in the Three-pronged Osmia’s laying. If I open a bramble-stump in the winter to examine the Osmia’s nest, I find it impossible, in the vast majority of cases, to distinguish positively between a female and a male cocoon: the difference in size is so small. The cells, moreover, have the same capacity: the diameter of the cylinder is the same throughout and the partitions are almost always the same distance apart. If I open it in July, the victualling-period, it is impossible for me to distinguish between the provisions destined for the males and those destined for the females. The measurement of the column of honey gives practically the same depth in all the cells. We find an equal quantity of space and food for both sexes.
This result makes us foresee what a direct examination of the two sexes in the adult form tells us. The male does not differ materially from the female in respect of size. If he is a trifle smaller, it is scarcely noticeable, whereas, in the Horned Osmia and the Three- horned Osmia, the male is only half or a third the size of the female, as we have seen from the respective bulk of their cocoons. In the Mason-bee of the Walls there is also a difference in size, though less pronounced.
The Three-pronged Osmia has not therefore to trouble about adjusting the dimensions of the dwelling and the quantity of the food to the sex of the egg which she is about to lay; the measure is the same from one end of the series to the other. It does not matter if the sexes alternate without order: one and all will find what they need, whatever their position in the row. The two other Osmiae, with their great disparity in size between the two sexes, have to be careful about the twofold consideration of board and lodging. And that, I think, is why they begin with spacious cells and generous rations for the homes of the females and end with narrow, scantily-provisioned cells, the homes of the males. With this sequence, sharply defined for the two sexes, there is less fear of mistakes which might give to one what belongs to another. If this is not the explanation of the facts, I see no other.
The more I thought about this curious question, the more probable it appeared to me that the irregular series of the Three-pronged Osmia and the regular series of the other Osmiae, of the Chalicodomae and of the Bees in general were all traceable to a common law. It seemed to me that the arrangement in a succession first of females and then of males did not account for everything. There must be something more. And I was right: that arrangement in series is only a tiny fraction of the reality, which is remarkable in a very different way. This is what I am going to prove by experiment.
CHAPTER 4. THE MOTHER DECIDES THE SEX OF THE EGG.
I will begin with the Mason-bee of the Pebbles. (This is the same insect as the Mason-bee of the Walls. Cf. “The Mason-bees”: passim.– Translator’s Note.) The old nests are often used, when they are in good enough repair. Early in the season the mothers quarrel fiercely over them; and, when one of the Bees has taken possession of the coveted dome, she drives any stranger away from it. The old house is far from being a ruin, only it is perforated with as many holes as it once had occupants. The work of restoration is no great matter. The heap of earth due to the destruction of the lid by the outgoing tenant is taken out of the cell and flung away at a distance, atom by atom. The remnants of the cocoon are also thrown away, but not always, for the delicate silken wrapper sometimes adheres closely to the masonry.
The victualling of the renovated cell is now begun. Next comes the laying; and lastly the orifice is sealed with a mortar plug. A second cell is utilized in the same way, followed by a third and so on, one after the other, as long as any remain unoccupied and the mother’s ovaries are not exhausted. Finally, the dome receives, mainly over the apertures already plugged, a coat of plaster which makes the nest look like new. If she has not finished her laying, the mother goes in search of other old nests to complete it. Perhaps she does not decide to found a new establishment except when she can find no second-hand dwellings, which mean a great economy of time and labour. In short, among the countless number of nests which I have collected, I find many more ancient than recent ones.
How shall we distinguish one from the other? The outward aspect tells you nothing, owing to the great care taken by the Mason to restore the surface of the old dwelling equal to new. To resist the rigours of the winter, this surface must be impregnable. The mother knows that and therefore repairs the dome. Inside, it is another matter: the old nest stands revealed at once. There are cells whose provisions, at least a year old, are intact, but dried up or musty, because the egg has never developed. There are others containing a dead larva, reduced by time to a blackened, curled-up cylinder. There are some whence the perfect insect was never able to issue: the Chalicodoma wore herself out in trying to pierce the ceiling of her chamber; her strength failed her and she perished in the attempt. Others again and very many are occupied by ravagers, Leucopses (Cf. “The Mason-bees”: chapter 11.–Translator’s Note.) and Anthrax-flies, who will come out a good deal later, in July. Altogether, the house is far from having every room vacant; there are nearly always a considerable number occupied either by parasites that were still in the egg-stage at the time when the Mason-bee was at work or by damaged provisions, dried grubs or Chalicodomae in the perfect state who have died without being able to effect their deliverance.
Should all the rooms be available, a rare occurrence, there still remains a method of distinguishing between an ancient nest and a recent one. The cocoon, as I have said, adheres pretty closely to the walls; and the mother does not always take away this remnant, either because she is unable to do so, or because she considers the removal unnecessary. Thus the base of the new cocoon is set in the bottom of the old cocoon. This double wrapper points very clearly to two generations, two separate years. I have even found as many as three cocoons fitting one into another at their bases. Consequently, the nests of the Mason-bee of the Pebbles are able to do duty for three years, if not more. Eventually they become utter ruins, abandoned to the Spiders and to various smaller Bees or Wasps, who take up their quarters in the crumbling rooms.
As we see, an old nest is hardly ever capable of containing the Mason-bee’s entire laying, which calls for some fifteen apartments. The number of rooms at her disposal is most unequal, but always very small. It is saying much when there are enough to receive about half the laying. Four or five cells, sometimes two or even one: that is what the Mason usually finds in a nest that is not her own work. This large reduction is explained when we remember the numerous parasites that live upon the unfortunate Bee.
Now, how are the sexes distributed in those layings which are necessarily broken up between one old nest and another? They are distributed in such a way as utterly to upset the idea of an invariable succession first of females and then of males, the idea which occurs to us on examining the new nests. If this rule were a constant one, we should be bound to find in the old domes at one time only females, at another only males, according as the laying was at its first or at its second stage. The simultaneous presence of the two sexes would then correspond with the transition period between one stage and the next and should be very unusual. On the contrary, it is very common; and, however few cells there may be, we always find both females and males in the old nests, on the sole condition that the compartments have the regulation holding-capacity, a large capacity for the females, a lesser for the males, as we have seen.
The old male cells can be recognized by their position on the outer edges and by their capacity, measuring on an average the same as a column of sand 31 millimetres high in a glass tube 5 millimetres wide. (1.21 x .195 inches.–Translator’s Note.) These cells contain males of the second or third generation and none but males. In the old female cells, those in the middle, whose capacity is measured by a similar column of sand 45 millimetres high (1.75 inches.– Translator’s Note.), are females and none but females.
This presence of both sexes at a time, even when there are but two cells free, one spacious and the other small, proves in the plainest fashion that the regular distribution observed in the complete nests of recent production is here replaced by an irregular distribution, harmonizing with the number and holding-capacity of the chambers to be stocked. The Mason-bee has before her, let me suppose, only five vacant cells: two larger and three smaller. The total space at her disposal would do for about a third of the laying. Well, in the two large cells, she puts females; in the three small cells, she puts males.
As we find the same sort of thing in all the old nests, we must needs admit that the mother knows the sex of the egg which she is going to lay, because that egg is placed in a cell of the proper capacity. We can go further and admit that the mother alters the order of succession of the sexes at her pleasure, because her layings, between one old nest and another, are broken up into small groups of males and females according to the exigencies of space in the actual nest which she happens to be occupying.
Just now, in the new nest, we saw the Mason-bee arranging her total laying into series first of females and next of males; and here she is, mistress of an old nest of which she has not the power to alter the arrangement, breaking up her laying into sections comprising both sexes just as required by the conditions imposed upon her. She therefore decides the sex of the egg at will, for, without this prerogative, she could not, in the chambers of the nest which she owes to chance, deposit unerringly the sex for which those chambers were originally built; and this happens however small the number of chambers to be filled.
When the nest is new, I think I see a reason why the Mason-bee should seriate her laying into females and then males. Her nest is a half- sphere. That of the Mason-bee of the Shrubs is very nearly a sphere. Of all shapes, the spherical shape is the strongest. Now these two nests require an exceptional power of resistance. Without protection of any kind, they have to brave the weather, one on its pebble, the other on its bough. Their spherical configuration is therefore very practical.
The nest of the Mason-bee of the Walls consists of a cluster of upright cells backing against one another. For the whole to take a spherical form, the height of the chambers must diminish from the centre of the dome to the circumference. Their elevation is the sine of the meridian arc starting from the plane of the pebble. Therefore, if they are to have any solidity, there must be large cells in the middle and small cells at the edges. And, as the work begins with the central chambers and ends with those on the circumference, the laying of the females, destined for the large cells, must precede that of the males, destined for the small cells. So the females come first and the males at the finish.
This is all very well when the mother herself founds the dwelling, when she lays the first rows of bricks. But, when she is in the presence of an old nest, of which she is quite unable to alter the general arrangement, how is she to make use of the few vacant rooms, the large and the small alike, if the sex of the egg be already irrevocably fixed? She can only do so by abandoning the arrangement in two consecutive rows and accommodating her laying to the varied exigencies of the home. Either she finds it impossible to make an economical use of the old nest, a theory refuted by the evidence, or else she determines at will the sex of the egg which she is about to lay.
The Osmiae themselves will furnish the most conclusive evidence on the latter point. We have seen that these Bees are not generally miners, who themselves dig out the foundation of their cells. They make use of the old structures of others, or else of natural retreats, such as hollow stems, the spirals of empty shells and various hiding-places in walls, clay or wood. Their work is confined to repairs to the house, such as partitions and covers. There are plenty of these retreats; and the insect would always find first- class ones if it thought of going any distance to look for them. But the Osmia is a stay-at-home: she returns to her birth-place and clings to it with a patience extremely difficult to exhaust. It is here, in this little familiar corner, that she prefers to settle her progeny. But then the apartments are few in number and of all shapes and sizes. There are long and short ones, spacious ones and narrow. Short of expatriating herself, a Spartan course, she has to use them all, from first to last, for she has no choice. Guided by these considerations, I embarked on the experiments which I will now describe.
I have said how my study, on two separate occasions, became a populous hive, in which the Three-horned Osmia built her nests in the various appliances which I had prepared for her. Among these appliances, tubes, either of glass or reed, predominated. There were tubes of all lengths and widths. In the long tubes, entire or almost entire layings, with a series of females followed by a series of males, were deposited. As I have already referred to this result, I will not discuss it again. The short tubes were sufficiently varied in length to lodge one or other portion of the total laying. Basing my calculations on the respective lengths of the cocoons of the two sexes, on the thickness of the partitions and the final lid, I shortened some of these to the exact dimensions required for two cocoons only, of different sexes.
Well, these short tubes, whether of glass or reed, were seized upon as eagerly as the long tubes. Moreover, they yielded this splendid result: their contents, only a part of the total laying, always began with female and ended with male cocoons. This order was invariable; what varied was the number of cells in the long tubes and the proportion between the two sorts of cocoons, sometimes males predominating and sometimes females.
The experiment is of paramount importance; and it will perhaps make the result clearer if I quote one instance from among a multitude of similar cases. I give the preference to this particular instance because of the rather exceptional fertility of the laying. An Osmia marked on the thorax is watched, day by day, from the commencement to the end of her work. From the 1st to the 10th of May, she occupies a glass tube in which she lodges seven females followed by a male, which ends the series. From the 10th to the 17th of May, she colonizes a second tube, in which she lodges first three females and then three males. From the 17th to the 25th of May, a third tube, with three females and then two males. On the 26th of May, a fourth tube, which she abandons, probably because of its excessive width, after laying one female in it. Lastly, from the 26th to the 30th of May, a fifth tube, which she colonizes with two females and three males. Total: twenty-five Osmiae, including seventeen females and eight males. And it will not be superfluous to observe that these unfinished series do not in any way correspond with periods separated by intervals of rest. The laying is continuous, in so far as the variable condition of the atmosphere allows. As soon as one tube is full and closed, another is occupied by the Osmia without delay.
The tubes reduced to the exact length of two cells fulfilled my expectation in the great majority of cases: the lower cell was occupied by a female and the upper by a male. There were a few exceptions. More discerning than I in her estimate of what was strictly necessary, better-versed in the economy of space, the Osmia had found a way of lodging two females where I had only seen room for one female and a male.
This experiment speaks volumes. When confronted with tubes too small to receive all her family, she is in the same plight as the Mason-bee in the presence of an old nest. She thereupon acts exactly as the Chalicodoma does. She breaks up her laying, divides it into series as short as the room at her disposal demands; and each series begins with females and ends with males. This breaking up, on the one hand, into sections in all of which both sexes are represented and the division, on the other hand, of the entire laying into just two groups, one female, the other male, when the length of the tube permits, surely provide us with ample evidence of the insect’s power to regulate the sex of the egg according to the exigencies of space.
And besides the exigencies of space one might perhaps venture to add those connected with the earlier development of the males. These burst their cocoons a couple of weeks or more before the females; they are the first who hasten to the sweets of the almond-tree. In order to release themselves and emerge into the glad sunlight without disturbing the string of cocoons wherein their sisters are still sleeping, they must occupy the upper end of the row; and this, no doubt, is the reason that makes the Osmia end each of her broken layings with males. Being next to the door, these impatient ones will leave the home without upsetting the shells that are slower in hatching.
I experimented on Latreille’s Osmia, using short and even very short stumps of reed. All that I had to do was to lay them just beside the nests of the Mason-bee of the Sheds, nests beloved by this particular Osmia. Old, disused hurdles supplied me with reeds inhabited from end to end by the Horned Osmia. In both cases I obtained the same results and the same conclusions as with the Three-horned Osmia.
I return to the latter, nidifying under my eyes in some old nests of the Mason-bee of the Walls, which I had placed within her reach, mixed up with the tubes. Outside my study, I had never yet seen the Three-horned Osmia adopt that domicile. This may be due to the fact that these nests are isolated one by one in the fields; and the Osmia, who loves to feel herself surrounded by her kin and to work in plenty of company, refuses them because of this isolation. But on my table, finding them close to the tubes in which the others are working, she adopts them without hesitation.
The chambers presented by those old nests are more or less spacious according to the thickness of the coat of mortar which the Chalicodoma has laid over the assembled chambers. To leave her cell, the Mason-bee has to perforate not only the plug, the lid built at the mouth of the cell, but also the thick plaster wherewith the dome is strengthened at the end of the work. The perforation results in a vestibule which gives access to the chamber itself. It is this vestibule which is sometimes longer and sometimes shorter, whereas the corresponding chamber is of almost constant dimensions, in the case of the same sex, of course.
We will first consider the short vestibule, at the most large enough to receive the plug with which the Osmia will close up the lodging. There is then nothing at her disposal except the cell proper, a spacious apartment in which one of the Osmia’s females will find ample accommodation, for she is much smaller than the original occupant of the chamber, no matter the sex; but there is not room for two cocoons at a time, especially in view of the space taken up by the intervening partition. Well, in those large, well-built chambers, formerly the homes of Chalicodomae, the Osmia settles females and none but females.
Let us now consider the long vestibule. Here, a partition is constructed, encroaching slightly on the cell proper, and the residence is divided into two unequal storeys, a large room below, housing a female, and a narrow cabin above, containing a male.
When the length of the vestibule permits, allowing for the space required by the outer stopper, a third storey is built, smaller than the second; and another male is lodged in this cramped corner. In this way the old nest of the Mason-bee of the Pebbles is colonized, cell after cell, by a single mother.
The Osmia, as we see, is very frugal of the lodging that has fallen to her share; she makes the best possible use of it, giving to the females the spacious chambers of the Mason-bee and to the males the narrow vestibules, subdivided into storeys when this is feasible. Economy of space is the chief consideration, since her stay-at-home tastes do not allow her to indulge in distant quests. She has to employ the site which chance places at her disposal just as it is, now for a male and now for a female. Here we see displayed, more clearly than ever, her power of deciding the sex of the egg, in order to adapt it judiciously to the conditions of the house-room available.
I had offered at the same time to the Osmiae in my study some old nests of the Mason-bee of the Shrubs, which are clay spheroids with cylindrical cavities in them. These cavities are formed, as in the old nests of the Mason-bee of the Pebbles, of the cell properly so- called and of the exit-way which the perfect insect cut through the outer coating at the time of its deliverance. Their diameter is about seven millimetres (.273 inch.–Translator’s Note.); their depth at the centre of the heap is 23 millimetres (.897 inch.–Translator’s Note.); and at the edge averages 14 millimetres (.546 inch.– Translator’s Note.)
The deep central cells receive only the females of the Osmia; sometimes even the two sexes together, with a partition in the middle, the female occupying the lower and the male the upper storey. True, in such cases economy of space is strained to the utmost, the apartments provided by the Mason-bee of the Shrubs being very small as it is, despite their entrance-halls. Lastly, the deeper cavities on the circumference are allotted to females and the shallower to males.
I will add that a single mother peoples each nest and also that she proceeds from cell to cell without troubling to ascertain the depth. She goes from the centre to the edges, from the edges to the centre, from a deep cavity to a shallow cavity and vice versa, which she would not do if the sexes were to follow upon each other in a settled order. For greater certainty, I numbered the cells of one nest as each of them was closed. On opening them later, I was able to see that the sexes were not subjected to a chronological arrangement. Females were succeeded by males and these by females without its being possible for me to make out any regular sequence. Only–and this is the essential point–the deep cavities were allotted to the females and the shallow ones to the males.
We know that the Three-horned Osmia prefers to haunt the habitations of the Bees who nidify in populous colonies, such as the Mason-bee of the Sheds and the Hairy-footed Anthophora. Exercising the very greatest care, I broke up some great lumps of earth removed from the banks inhabited by the Anthophora and sent to me from Carpentras by my dear friend and pupil M. Devillario. I examined them conscientiously in the quiet of my study. I found the Osmia’s cocoons arranged in short series, in very irregular passages, the original work of which is due to the Anthophora. Touched up afterwards, made larger or smaller, lengthened or shortened, intersected with a network of crossings by the numerous generations that had succeeded one another in the same city, they formed an inextricable labyrinth.
Sometimes these corridors did not communicate with any adjoining apartment; sometimes they gave access to the spacious chamber of the Anthophora, which could be recognized, in spite of its age, by its oval shape and its coating of glazed stucco. In the latter case, the bottom cell, which once constituted, by itself, the chamber of the Anthophora, was always occupied by a female Osmia. Beyond it, in the narrow corridor, a male was lodged, not seldom two, or even three. Of course, clay partitions, the work of the Osmia, separated the different inhabitants, each of whom had his own storey, his own closed cell.
When the accommodation consisted of no more than a simple cylinder, with no state-bedroom at the end of it–a bedroom always reserved for a female–the contents varied with the diameter of the cylinder. The series, of which the longest were series of four, included, with a wider diameter, first one or two females, then one or two males. It also happened, though rarely, that the series was reversed, that is to say, it began with males and ended with females. Lastly, there were a good many isolated cocoons, of one sex or the other. When the cocoon was alone and occupied the Anthophora’s cell, it invariably belonged to a female.
I have observed the same thing in the nests of the Mason-bee of the Sheds, but not so easily. The series are shorter here, because the Mason-bee does not bore galleries but builds cell upon cell. The work of the whole swarm thus forms a stratum of cells that grows thicker from year to year. The corridors occupied by the Osmia are the holes which the Mason-bee dug in order to reach daylight from the deep layers. In these short series, both sexes are usually present; and, if the Mason-bee’s chamber is at the end of the passage, it is inhabited by a female Osmia.
We come back to what the short tubes and the old nests of the Mason- bee of the Pebbles have already taught us. The Osmia who, in tubes of sufficient length, divides her whole laying into a continuous sequence of females and a continuous sequence of males, now breaks it up into short series in which both sexes are present. She adapts her sectional layings to the exigencies of a chance lodging; she always places a female in the sumptuous chamber which the Mason-bee or the Anthophora occupied originally.
Facts even more striking are supplied by the old nests of the Masked Anthophora (A. personata, ILLIG.), old nests which I have seen utilized by the Horned Osmia and the Three-horned Osmia at the same time. Less frequently, the same nests serve for Latreille’s Osmia. Let us first describe the Masked Anthophora’s nests.
In a steep bank of sandy clay, we find a set of round, wide-open holes. There are generally only a few of them, each about half an inch in diameter. They are the entrance-doors leading to the Anthophora’s abode, doors always left open, even after the building is finished. Each of them gives access to a short passage, sometimes straight, sometimes winding, nearly horizontal, polished with minute care and varnished with a sort of white glaze. It looks as if it had received a thin coat of whitewash. On the inner surface of this passage, in the thickness of the earthy bank, spacious oval niches have been excavated, communicating with the corridor by means of a narrow bottle-neck, which is closed, when the work is done, with a substantial mortar stopper. The Anthophora polishes the outside of this stopper so well, smooths its surface so perfectly, bringing it to the same level as that of the passage, is so careful to give it the white tint of the rest of the wall that, when the job is finished, it becomes absolutely impossible to distinguish the entrance-door corresponding with each cell.
The cell is an oval cavity dug in the earthy mass. The wall has the same polish, the same chalky whiteness as the general passage. But the Anthophora does not limit herself to digging oval niches: to make her work more solid, she pours over the walls of the chamber a salivary liquid which not only whitens and varnishes but also penetrates to a depth of some millimetres into the sandy earth, which it turns into a hard cement. A similar precaution is taken with the passage; and therefore the whole is a solid piece of work capable of remaining in excellent condition for years.
Moreover, thanks to the wall hardened by the salivary fluid, the structure can be removed from its matrix by chipping it carefully away. We thus obtain, at least in fragments, a serpentine tube from which hangs a single or double row of oval nodules that look like large grapes drawn out lengthwise. Each of these nodules is a cell, the entrance to which, carefully hidden, opens into the tube or passage. When she wishes to leave her cell, in the spring, the Anthophora destroys the mortar disk that closes the jar and thus reaches the general corridor, which is quite open to the outer air. The abandoned nest provides a series of pear-shaped cavities, of which the distended part is the old cell and the contracted part the exit-neck, rid of its stopper.
These pear-shaped hollows form splendid lodgings, impregnable strongholds, in which the Osmiae find a safe and commodious retreat for their families. The Horned Osmia and the Three-horned Osmia establish themselves there at the same time. Although it is a little too large for her, Latrielle’s Osmia also appears very well satisfied with it.
I have examined some forty of the superb cells utilized by each of the first two. The great majority are divided into two storeys by means of a transversal partition. The lower storey includes the larger portion of the Anthophora’s cell; the upper storey includes the rest of the cell and a little of the bottle-neck that surmounts it. The two-roomed dwelling is closed, in the passage, by a shapeless, bulky mass of dried mud. What a clumsy artist the Osmia is, compared with the Anthophora! Against the exquisite work of the Anthophora, partition and plug strike a note as hideously incongruous as a lump of dirt on polished marble.
The two apartments thus obtained are of a very unequal capacity, which at once strikes the observer. I measured them with my five- millimetre tube. On an average, the bottom one is represented by a column of sand 50 millimetres deep (1.95 inches.–Translator’s Note.) and the top one by a column of 15 millimetres (.585 inch.– Translator’s Note.). The holding-capacity of the one is therefore about three times as large as that of the other. The cocoons enclosed present the same disparity. The bottom one is big, the top one small. Lastly, the lower one belongs to a female Osmia and the upper to a male Osmia.
Occasionally the length of the bottle-neck allows of a fresh arrangement and the cavity is divided into three storeys. The bottom one, which is always the most spacious, contains a female; the two above, both smaller than the first and one smaller than the other, contain males.
Let us keep to the first case, which is always the most frequent. The Osmia is in the presence of one of these pear-shaped hollows. It is a find that must be employed to the best advantage: a prize of this sort is rare and falls only to fortune’s favourites. To lodge two females in it at once is impossible; there is not sufficient room. To lodge two males in it would be undue generosity to a sex that is entitled to but the smallest consideration. Besides, the two sexes must be represented in almost equal numbers. The Osmia decides upon one female, whose portion shall be the better room, the lower one, which is larger, better-protected and more nicely polished, and one male, whose portion shall be the upper storey, a cramped attic, uneven and rugged in the part which encroaches on the bottle-neck. This decision is proved by numerous undeniable facts. Both Osmiae therefore can choose the sex of the egg about to be laid, seeing that they are now breaking up the laying into groups of two, a female and a male, as required by the conditions of the lodging.
I have only once found Latreille’s Osmia established in the nest of the Masked Anthophora. She had occupied but a small number of cells, because the others were not free, being inhabited by the Anthophora. The cells in question were divided into three storeys by partitions of green mortar; the lower storey was occupied by a female, the two others by males, with smaller cocoons.
I came to an even more remarkable example. Two Anthidia of my district, A. septemdentatum, LATR., and A. bellicosum, LEP., adopt as the home of their offspring the empty shells of different snails: Helix aspersa, H. algira, H. nemoralis, H. caespitum. The first- named, the Common Snail, is the most often used, under the stone- heaps and in the crevices of old walls. Both Anthidia colonize only the second whorl of the spiral. The central part is too small and remains unoccupied. Even so with the front whorl, the largest, which is left completely empty, so much so that, on looking through the opening, it is impossible to tell whether the shell does or does not contain the Bee’s nest. We have to break this last whorl if we would perceive the curious nest tucked away in the spiral.
We then find first a transversal partition, formed of tiny bits of gravel cemented by a putty made from resin, which is collected in fresh drops from the oxycedrus and the Aleppo pine. Beyond this is a stout barricade made up of rubbish of all kinds: bits of gravel, scraps of earth, juniper-needles, the catkins of the conifers, small shells, dried excretions of Snails. Next come a partition of pure resin, a large cocoon in a roomy chamber, a second partition of pure resin and, lastly, a smaller cocoon in a narrow chamber. The inequality of the two cells is the necessary consequence of the shape of the shell, whose inner space gains rapidly in width as the spiral gets nearer to the orifice. Thus, by the mere general arrangement of the home and without any work on the Bee’s part beyond some slender partitions, a large room is marked out in front and a much smaller room at the back.
By a very remarkable exception, which I have mentioned casually elsewhere, the males of the genus Anthidium are generally larger than the females; and this is the case with the two species in particular that divide the Snail’s spiral with resin partitions. I collected some dozens of nests of both species. In at least half the cases, the two sexes were present together; the female, the smaller, occupied the front cell and the male, the bigger, the back cell. Other cells, which were smaller or too much obstructed at the back by the dried-up remains of the Mollusc, contained only one cell, occupied at one time by a female and at another by a male. A few, lastly, had both cells inhabited now by two males and now by two females. The most frequent arrangement was the simultaneous presence of both sexes, with the female in front and the male behind. The Anthidia who make resin- dough and live in Snail-shells can therefore alternate the sexes regularly to meet the exigencies of the spiral dwelling-house.
One more thing and I have done. My apparatus of reeds, fixed against the walls of the garden, supplied me with a remarkable nest of the Horned Osmia. The nest is established in a bit of reed 11 millimetres wide inside. (.429 inch–Translator’s Note.) It comprises thirteen cells and occupies only half the cylinder, although the orifice is plugged with the usual stopper. The laying therefore seems here to be complete.
Well, this laying is arranged in a most singular fashion. There is first, at a suitable distance from the bottom or the node of the reed, a transversal partition, perpendicular to the axis of the tube. This marks off a cell of unusual size, in which a female is lodged. After that, in view of the excessive width of the tunnel, which is too great for a series in single file, the Osmia appears to alter her mind. She therefore builds a partition perpendicular to the transversal partition which she has just constructed and thus divides the second storey into two rooms, a larger room, in which she lodges a female, and a smaller, in which she lodges a male. She next builds a second transversal partition and a second longitudinal partition perpendicular to it. These once more give two unequal chambers, stocked likewise, the large one with a female, the smaller one with a male.
>From this third storey onwards, the Osmia abandons geometrical accuracy; the architect seems to be a little out in her reckoning. The transversal partitions become more and more slanting and the work grows irregular, but always with a sprinkling of large chambers for the females and small chambers for the males. Three females and two males are housed in this way, the sexes alternating.
By the time that the base of the eleventh cell is reached, the transversal partition is once more almost perpendicular to the axis. Here what happened at the bottom is repeated. There is no longitudinal partition; and the spacious cell, covering the whole diameter of the cylinder, receives a female. The edifice ends with two transversal partitions and one longitudinal partition, which mark out, on the same level, chambers twelve and thirteen, both of which contain males.
There is nothing more curious than this mixing of the two sexes, when we know with what precision the Osmia separates them in a linear series, where the narrow width of the cylinder demands that the cells shall be set singly, one above the other. Here, the Bee is making use of a tube whose diameter is not suited to her work; she is constructing a complex and difficult edifice, which perhaps would not possess the necessary solidity if the ceilings were too broad. The Osmia therefore supports these ceilings with longitudinal partitions; and the unequal chambers resulting from the introduction of these partitions receive females at one time and males at another, according to their capacity.
CHAPTER 5. PERMUTATIONS OF SEX.
The sex of the egg is optional. The choice rests with the mother, who is guided by considerations of space and, according to the accommodation at her disposal, which is frequently fortuitous and incapable of modification, places a female in this cell and a male in that, so that both may have a dwelling of a size suited to their unequal development. This is the unimpeachable evidence of the numerous and varied facts which I have set forth. People unfamiliar with insect anatomy–the public for whom I write–would probably give the following explanation of this marvellous prerogative of the Bee: the mother has at her disposal a certain number of eggs, some of which are irrevocably female and the others irrevocably male: she is able to pick out of either group the one which she wants at the actual moment; and her choice is decided by the holding capacity of the cell that has to be stocked. Everything would then be limited to a judicious selection from the heap of eggs.
Should this idea occur to him, the reader must hasten to reject it. Nothing could be more false, as the merest reference to anatomy will show. The female reproductive apparatus of the Hymenoptera consists generally of six ovarian tubes, something like glove-fingers, divided into bunches of three and ending in a common canal, the oviduct, which carries the eggs outside. Each of these glove-fingers is fairly wide at the base, but tapers sharply towards the tip, which is closed. It contains, arranged in a row, one after the other, like beads on a string, a certain number of eggs, five or six for instance, of which the lower ones are more or less developed, the middle ones half-way towards maturity, and the upper ones very rudimentary. Every stage of evolution is here represented, distributed regularly from bottom to top, from the verge of maturity to the vague outlines of the embryo. The sheath clasps its string of ovules so closely that any inversion of the order is impossible. Besides, an inversion would result in a gross absurdity: the replacing of a riper egg by another in an earlier stage of development.
Therefore, in each ovarian tube, in each glove-finger, the emergence of the eggs occurs according to the order governing their arrangement in the common sheath; and any other sequence is absolutely impossible. Moreover, at the nesting period, the six ovarian sheaths, one by one and each in its turn, have at their base an egg which in a very short time swells enormously. Some hours or even a day before the laying, that egg by itself represents or even exceeds in bulk the whole of the ovigenous apparatus. This is the egg which is on the point of being laid. It is about to descend into the oviduct, in its proper order, at its proper time; and the mother has no power to make another take its place. It is this egg, necessarily this egg and no other, that will presently be laid upon the provisions, whether these be a mess of honey or a live prey; it alone is ripe, it alone is at the entrance to the oviduct; none of the others, since they are farther back in the row and not at the right stage of development, can be substituted at this crisis. Its birth is inevitable.
What will it yield, a male or a female? No lodging has been prepared, no food collected for it; and yet both food and lodging have to be in keeping with the sex that will proceed from it. And here is a much more puzzling condition: the sex of that egg, whose advent is predestined, has to correspond with the space which the mother happens to have found for a cell. There is therefore no room for hesitation, strange though the statement may appear: the egg, as it descends from its ovarian tube, has no determined sex. It is perhaps during the few hours of its rapid development at the base of its ovarian sheath, it is perhaps on its passage through the oviduct that it receives, at the mother’s pleasure, the final impress that will produce, to match the cradle which it has to fill, either a female or a male.
Thereupon the following question presents itself. Let us admit that, when the normal conditions remain, a laying would have yielded m females and n males. Then, if my conclusions are correct, it must be in the mother’s power, when the conditions are different, to take from the m group and increase the n group to the same extent; it must be possible for her laying to be represented as m-1, m-2, m-3, etc. females and by n+1, n+2, n+3, etc. males, the sum of m+n remaining constant, but one of the sexes being partly permuted into the other. The ultimate conclusion even cannot be disregarded: we must admit a set of eggs represented by m-m, or zero, females and of n+m males, one of the sexes being completely replaced by the other. Conversely, it must be possible for the feminine series to be augmented from the masculine series to the extent of absorbing it entirely. It was to solve this question and some others connected with it that I undertook, for the second time, to rear the Three-horned Osmia in my study.
The problem on this occasion is a more delicate one; but I am also better-equipped. My apparatus consists of two small, closed packing- cases, with the front side of each pierced with forty holes, in which I can insert my glass tubes and keep them in a horizontal position. I thus obtain for the Bees the darkness and mystery which suit their work and for myself the power of withdrawing from my hive, at any time, any tube that I wish, with the Osmia inside, so as to carry it to the light and follow, if need be with the aid of the lens, the operations of the busy worker. My investigations, however frequent and minute, in no way hinder the peaceable Bee, who remains absorbed in her maternal duties.
I mark a plentiful number of my guests with a variety of dots on the thorax, which enables me to follow any one Osmia from the beginning to the end of her laying. The tubes and their respective holes are numbered; a list, always lying open on my desk, enables me to note from day to day, sometimes from hour to hour, what happens in each tube and particularly the actions of the Osmiae whose backs bear distinguishing marks. As soon as one tube is filled, I replace it by another. Moreover, I have scattered in front of either hive a few handfuls of empty Snail-shells, specially chosen for the object which I have in view. Reasons which I will explain later led me to prefer the shells of Helix caespitum. Each of the shells, as and when stocked, received the date of the laying and the alphabetical sign corresponding with the Osmia to whom it belonged. In this way, I spent five or six weeks in continual observation. To succeed in an enquiry, the first and foremost condition is patience. This condition I fulfilled; and it was rewarded with the success which I was justified in expecting.
The tubes employed are of two kinds. The first, which are cylindrical and of the same width throughout, will be of use for confirming the facts observed in the first year of my experiments in indoor rearing. The others, the majority, consist of two cylinders which are of very different diameters, set end to end. The front cylinder, the one which projects a little way outside the hive and forms the entrance- hole, varies in width between 8 and 12 millimetres. (Between .312 to .468 inch.–Translator’s Note.) The second, the back one, contained entirely within my packing-case, is closed at its far end and is 5 to 6 millimetres (.195 to .234 inch.–Translator’s Note.) in diameter. Each of the two parts of the double-galleried tunnel, one narrow and one wide, measures at most a decimetre (3.9 inches.–Translator’s Note.) in length. I thought it advisable to have these short tubes, as the Osmia is thus compelled to select different lodgings, each of them being insufficient in itself to accommodate the total laying. In this way I shall obtain a greater variety in the distribution of the sexes. Lastly, at the mouth of each tube, which projects slightly outside the case, there is a little paper tongue, forming a sort of perch on which the Osmia alights on her arrival and giving easy access to the house. With these facilities, the swarm colonized fifty-two double-galleried tubes, thirty-seven cylindrical tubes, seventy-eight Snail-shells and a few old nests of the Mason-bee of the Shrubs. From this rich mine of material I will take what I want to prove my case.
Every series, even when incomplete, begins with females and ends with males. To this rule I have not yet found an exception, at least in galleries of normal diameter. In each new abode, the mother busies herself first of all with the more important sex. Bearing this point in mind, would it be possible for me, by manoeuvring, to obtain an inversion of this order and make the laying begin with males? I think so, from the results already ascertained and the irresistible conclusions to be drawn from them. The double-galleried tubes are installed in order to put my conjectures to the proof.
The back gallery, 5 or 6 millimetres (.195 to .234 inch.– Translator’s Note.) wide, is too narrow to serve as a lodging for normally developed females. If, therefore, the Osmia, who is very economical of her space, wishes to occupy them, she will be obliged to establish males there. And her laying must necessarily begin here, because this corner is the rear-most part of the tube. The foremost gallery is wide, with an entrance-door on the front of the hive. Here, finding the conditions to which she is accustomed, the mother will go on with her laying in the order which she prefers.
Let us now see what has happened. Of the fifty-two double galleried tubes, about a third did not have their narrow passage colonized. The Osmia closed its aperture communicating with the large passage; and the latter alone received the eggs. This waste of space was inevitable. The female Osmiae, though nearly always larger than the males, present marked differences among one another: some are bigger, some are smaller. I had to adjust the width of the narrow galleries to Bees of average dimensions. It may happen therefore that a gallery is too small to admit the large-sized mothers to whom chance allots it. When the Osmia is unable to enter the tube, obviously she will not colonize it. She then closes the entrance to this space which she cannot use and does her laying beyond it, in the wide tube. Had I tried to avoid these useless apparatus by choosing tubes of larger calibre, I should have encountered another drawback: the medium-sized mothers, finding themselves almost comfortable, would have decided to lodge females there. I had to be prepared for it: as each mother selected her house at will and as I was unable to interfere in her choice, a narrow tube would be colonized or not, according as the Osmia who owned it was or was not able to make her way inside.
There remain some forty pairs of tubes with both galleries colonized. In these there are two things to take into consideration. The narrow rear tubes of 5 or 5 1/2 millimetres (.195 to .214 inch.– Translator’s Note.)–and these are the most numerous–contain males and males only, but in short series, between one and five. The mother is here so much hampered in her work that they are rarely occupied from end to end; the Osmia seems in a hurry to leave them and to go and colonize the front tube, whose ample space will leave her the liberty of movement necessary for her operations. The other rear tubes, the minority, whose diameter is about 6 millimetres (.234 inch.–Translator’s Note.), contain sometimes only females and sometimes females at the back and males towards the opening. One can see that a tube a trifle wider and a mother slightly smaller would account for this difference in the results. Nevertheless, as the necessary space for a female is barely provided in this case, we see that the mother avoids as far as she can a two-sex arrangement beginning with males and that she adopts it only in the last extremity. Finally, whatever the contents of the small tube may be, those of the large one, following upon it, never vary and consist of females at the back and males in front.
Though incomplete, because of circumstances very difficult to control, the result of the experiment is none the less very striking. Twenty-five apparatus contain only males in their narrow gallery, in numbers varying from a minimum of one to a maximum of five. After these comes the colony of the large gallery, beginning with females and ending with males. And the layings in these apparatus do not always belong to late summer or even to the intermediate period: a few small tubes contain the earliest eggs of the Osmiae. A couple of Osmiae, more forward than the others, set to work on the 23rd of April. Both of them started their laying by placing males in the narrow tubes. The meagre supply of provisions was enough in itself to show the sex, which proved later to be in accordance with my anticipations. We see then that, by my artifices, the whole swarm starts with the converse of the normal order. This inversion is continued, at no matter what period, from the beginning to the end of the operations. The series which, according to rule, would begin with females now begins with males. Once the larger gallery is reached, the laying is pursued in the usual order.
We have advanced one step and that no small one: we have seen that the Osmia, when circumstances require it, is capable of reversing the sequence of the sexes. Would it be possible, provided that the tube were long enough, to obtain a complete inversion, in which the entire series of the males should occupy the narrow gallery at the back and the entire series of the females the roomy gallery in front? I think not; and I will tell you why.
Long and narrow cylinders are by no means to the Osmia’s taste, not because of their narrowness but because of their length. Remember that for each load of honey brought the worker is obliged to move backwards twice. She enters, head first, to begin by disgorging the honey-syrup from her crop. Unable to turn in a passage which she blocks entirely, she goes out backwards, crawling rather than walking, a laborious performance on the polished surface of the glass and a performance which, with any other surface, would still be very awkward, as the wings are bound to rub against the wall with their free end and are liable to get rumpled or bent. She goes out backwards, reaches the outside, turns round and goes in again, but this time the opposite way, so as to brush off the load of pollen from her abdomen on to the heap. If the gallery is at all long, this crawling backwards becomes troublesome after a time; and the Osmia soon abandons a passage that is too small to allow of free movement. I have said that the narrow tubes of my apparatus are, for the most part, only very incompletely colonized. The Bee, after lodging a small number of males in them, hastens to leave them. In the wide front gallery, she can stay where she is and still be able to turn round easily for her different manipulations; she will avoid those two long journeys backwards, which are so exhausting and so bad for her wings.
Another reason no doubt prompts her not to make too great a use of the narrow passage, in which she would establish males, followed by females in the part where the gallery widens. The males have to leave their cells a couple of weeks or more before the females. If they occupy the back of the house, they will die prisoners or else they will overturn everything on their way out. This risk is avoided by the order which the Osmia adopts.
In my tubes with their unusual arrangement, the mother might well find the dilemma perplexing: there is the narrowness of the space at her disposal and there is the emergence later on. In the narrow tubes, the width is insufficient for the females; on the other hand, if she lodges males there, they are liable to perish, since they will be prevented from issuing at the proper moment. This would perhaps explain the mother’s hesitation and her obstinacy in settling females in some of my apparatus which looked as if they could suit none but males.
A suspicion occurs to me, a suspicion aroused by my attentive examination of the narrow tubes. All, whatever the number of their inmates, are carefully plugged at the opening, just as separate tubes would be. It might therefore be the case that the narrow gallery at the back was looked upon by the Osmia not as the prolongation of the large front gallery, but as an independent tube. The facility with which the worker turns as soon as she reaches the wide tube, her liberty of action, which is now as great as in a doorway communicating with the outer air, might well be misleading and cause the Osmia to treat the narrow passage at the back as though the wide passage in front did not exist. This would account for the placing of the female in the large tube above the males in the small tube, an arrangement contrary to her custom.
I will not undertake to decide whether the mother really appreciates the danger of my snares, or whether she makes a mistake in considering only the space at her disposal and beginning with males. At any rate, I perceive in her a tendency to deviate as little as possible from the order which safeguards the emergence of the two sexes. This tendency is demonstrated by her repugnance to colonizing my narrow tubes with long series of males. However, so far as we are concerned, it does not matter much what passes at such times in the Osmia’s little brain. Enough for us to know that she dislikes narrow and long tubes, not because they are narrow, but because they are at the same time long.
And, in fact, she does very well with a short tube of the same diameter. Such are the cells in the old nests of the Mason-bee of the Shrubs and the empty shells of the Garden Snail. With the short tube, the two disadvantages of the long tube are avoided. She has very little of that crawling backwards to do when she has a Snail-shell for the home of her eggs and scarcely any when the home is the cell of the Mason-bee. Moreover, as the stack of cocoons numbers two or three at most, the deliverance will be exempt from the difficulties attached to a long series. To persuade the Osmia to nidify in a single tube long enough to receive the whole of her laying and at the same time narrow enough to leave her only just the possibility of admittance appears to me a project without the slightest chance of success: the Bee would stubbornly refuse such a dwelling or would content herself with entrusting only a very small portion of her eggs to it. On the other hand, with narrow but short cavities, success, without being easy, seems to me at least quite possible. Guided by these considerations, I embarked upon the most arduous part of my problem: to obtain the complete or almost complete permutation of one sex with the other; to produce a laying consisting only of males by offering the mother a series of lodgings suited only to males.
Let us in the first place consult the old nests of the Mason-bee of the Shrubs. I have said that these mortar spheroids, pierced all over with little cylindrical cavities, are adopted pretty eagerly by the Three-horned Osmia, who colonizes them before my eyes with females in the deep cells and males in the shallow cells. That is how things go when the old nest remains in its natural state. With a grater, however, I scrape the outside of another nest so as to reduce the depth of the cavities to some ten millimetres. (About two-fifths of an inch.–Translator’s Note.) This leaves in each cell just room for one cocoon, surmounted by the closing stopper. Of the fourteen cavities in the nests, I leave two intact, measuring fifteen millimetres in depth. (.585 inch.–Translator’s Note.) Nothing could be more striking than the result of this experiment, made in the first year of my home rearing. The twelve cavities whose depth had been reduced all received males; the two cavities left untouched received females.
A year passes and I repeat the experiment with a nest of fifteen cells; but this time all the cells are reduced to the minimum depth with the grater. Well, the fifteen cells, from first to last, are occupied by males. It must be quite understood that, in each case, all the offspring belonged to one mother, marked with her distinguishing spot and kept in sight as long as her laying lasted. He would indeed be difficult to please who refused to bow before the results of these two experiments. If, however, he is not yet convinced, here is something to remove his last doubts.
The Three-horned Osmia often settles her family in old shells, especially those of the Common Snail (Helix aspersa), who is so common under the stone-heaps and in the crevices of the little unmortared walls that support our terraces. In this species, the spiral is wide open, so that the Osmia, penetrating as far down as the helical passage permits, finds, immediately above the point which is too narrow to pass, the space necessary for the cell of a female. This cell is succeeded by others, wider still, always for females, arranged in a line in the same way as in a straight tube. In the last whorl of the spiral, the diameter would be too great for a single row. Then longitudinal partitions are added to the transverse partitions, the whole resulting in cells of unequal dimensions in which males predominate, mixed with a few females in the lower storeys. The sequence of the sexes is therefore what it would be in a straight tube and especially in a tube with a wide bore, where the partitioning is complicated by subdivisions on the same level. A single Snail-shell contains room for six or eight cells. A large, rough earthen stopper finishes the nest at the entrance to the shell.
As a dwelling of this sort could show us nothing new, I chose for my swarm the Garden Snail (Helix caespitum), whose shell, shaped like a small, swollen Ammonite, widens by slow degrees, the diameter of the usable portion, right up to the mouth, being hardly greater than that required by a male Osmia-cocoon. Moreover, the widest part, in which a female might find room, has to receive a thick stopping-plug, below which there will often be a free space. Under all these conditions, the house will hardly suit any but males arranged one after the other.
The collection of shells placed at the foot of each hive includes specimens of different sizes. The smallest are 18 millimetres (.7 inch.–Translator’s Note.) in diameter and the largest 24 millimetres (.936 inch.–Translator’s Note.) There is room for two cocoons, or three at most, according to their dimensions.
Now these shells were used by my visitors without any hesitation, perhaps even with more eagerness than the glass tubes, whose slippery sides might easily be a little annoying to the Bee. Some of them were occupied on the first few days of the laying; and the Osmia who had started with a home of this sort would pass next to a second Snail- shell, in the immediate neighbourhood of the first, to a third, a fourth and others still, always close to one another, until her ovaries were emptied. The whole family of one mother would thus be lodged in Snail-shells which were duly marked with the date of the laying and a description of the worker. The faithful adherents of the Snail-shell were in the minority. The greater number left the tubes to come to the shells and then went back from the shells to the tubes. All, after filling the spiral staircase with two or three cells, closed the house with a thick earthen stopper on a level with the opening. It was a long and troublesome task, in which the Osmia displayed all her patience as a mother and all her talents as a plasterer. There were even some who, scrupulous to excess, carefully cemented the umbilicus, a hole which seemed to inspire them with distrust as being able to give access to the interior of the dwelling. It was a dangerous-looking cavity, which for the greater safety of the family it was prudent to block up.
When the pupae are sufficiently matured, I proceed to examine these elegant abodes. The contents fill me with joy: they fulfil my anticipations to the letter. The great, the very great majority of the cocoons turn out to be males; here and there, in the bigger cells, a few rare females appear. The smallness of the space has almost done away with the sixty-eight Snail-shells colonized. But, of this total number, I must use only those series which received an entire laying and were occupied by the same Osmia from the beginning to the end of the egg-season. Here are a few examples, taken from among the most conclusive.
>From the 6th of May, when she started operations, to the 25th of May, the date at which her laying ceased, the Osmia occupied seven Snail- shells in succession. Her family consists of fourteen cocoons, a number very near the average; and, of these fourteen cocoons, twelve belong to males and only two to females. These occupy the seventh and thirteenth places in chronological order.
Another, between the 9th and 27th of May, stocked six Snail-shells with a family of thirteen, including ten males and three females. The places occupied by the latter in the series were numbers 3, 4 and 5.
A third, between the 2nd and 29th of May, colonized eleven Snail- shells, a prodigious task. This industrious one was also exceedingly prolific. She supplied me with a family of twenty-six, the largest which I have ever obtained from one Osmia. Well, this abnormal progeny consisted of twenty-five males and one female, one alone, occupying place 17.
There is no need to go on, after this magnificent example, especially as the other series would all, without exception, give us the same result. Two facts are immediately obvious. The Osmia is able to reverse the order of her laying and to start with a more or less long series of males before producing any females. In the first case, the first female appears as number 7; in the third, as number 17. There is something better still; and this is the proposition which I was particularly anxious to prove: the female sex can be permuted with the male sex and can be permuted to the point of disappearing altogether. We see this especially in the third case, where the presence of a solitary female in a family of twenty-six is due to the somewhat larger diameter of the corresponding Snail-shell and also, no doubt, to some mistake on the mother’s part, for the female cocoon, in a series of two, occupies the upper storey, the one next to the orifice, an arrangement which the Osmia appears to me to dislike.
This result throws so much light on one of the darkest corners of biology that I must attempt to corroborate it by means of even more conclusive experiments. I propose next year to give the Osmiae nothing but Snail-shells for a lodging, picked out one by one, and rigorously to deprive the swarm of any other retreat in which the laying could be effected. Under these conditions, I ought to obtain nothing but males, or nearly, for the whole swarm.
There would still remain the inverse permutation: to obtain only females and no males, or very few. The first permutation makes the second seem very probable, although I cannot as yet conceive a means of realizing it. The only condition which I can regulate is the dimensions of the home. When the rooms are small, the males abound and the females tend to disappear. With generous quarters, the converse would not take place. I should obtain females and afterwards an equal number of males, confined in small cells which, in case of need, would be bounded by numerous partitions. The factor of space does not enter into the question here. What artifice can we then employ to provoke this second permutation? So far, I can think of nothing that is worth attempting.
It is time to conclude. Leading a retired life, in the solitude of a village, having quite enough to do with patiently and obscurely ploughing my humble furrow, I know little about modern scientific views. In my young days I had a passionate longing for books and found it difficult to procure them; to-day, when I could almost have them if I wanted, I am ceasing to wish for them. It is what usually happens as life goes on. I do not therefore know what may have been done in the direction whither this study of the sexes has led us. If I am stating propositions that are really new or at least more comprehensive than the propositions already known, my words will perhaps sound heretical. No matter: as a simple translator of facts, I do not hesitate to make my statement, being fully persuaded that time will turn my heresy into orthodoxy. I will therefore recapitulate my conclusions.
Bees lay their eggs in series of first females and then males, when the two sexes are of different sizes and demand an unequal quantity of nourishment. When the two sexes are alike in size, the same sequence may occur, but less regularly.
This dual arrangement disappears when the place chosen for the nest is not large enough to contain the entire laying. We then see broken layings, beginning with females and ending with males.
The egg, as it issues from the ovary, has not yet a fixed sex. The final impress that produces the sex is given at the moment of laying or a little before.
So as to be able to give each larva the amount of space and food that suits it according as it is male or female, the mother can choose the sex of the egg which she is about to lay. To meet the conditions of the building, which is often the work of another or else a natural retreat that admits of little or no alteration, she lays either a male egg or a female egg as she pleases. The distribution of the sexes depends upon herself. Should circumstances require it, the order of the laying can be reversed and begin with males; lastly, the entire laying can contain only one sex.
The same privilege is possessed by the predatory Hymenoptera, the Wasps, at least by those in whom the two sexes are of a different size and consequently require an amount of nourishment that is larger in the one case than in the other. The mother must know the sex of the egg which she is going to lay; she must be able to choose the sex of that egg so that each larva may obtain its proper portion of food.
Generally speaking, when the sexes are of different sizes, every insect that collects food and prepares or selects a dwelling for its offspring must be able to choose the sex of the egg in order to satisfy without mistake the conditions imposed upon it.
The question remains how this optional assessment of the sexes is effected. I know absolutely nothing about it. If I should ever learn anything about this delicate point, I shall owe it to some happy chance for which I must wait, or rather watch, patiently. Towards the end of my investigations, I heard of a German theory which relates to the Hive-bee and comes from Dzierzon, the apiarist. (Johann Dzierzon, author of “Theorie und Praxis des neuen Bienenfreundes.”– Translator’s Note.) If I understand it aright, according to the very incomplete documents which I have before me, the egg, as it issues from the ovary, is said already to possess a sex, which is always the same; it is originally male; and it becomes female by fertilization. The males are supposed to proceed from non-fertilized eggs, the females from fertilized eggs. The Queen-bee would thus lay female eggs or male eggs according as she fertilized them or not while they were passing into her oviduct.
Coming from Germany, this theory cannot but inspire me with profound distrust. As it has been given acceptance, with rash precipitancy, in standard works, I will overcome my reluctance to devoting my attention to Teutonic ideas and will submit it not to the test of argument, which can always be met by an opposite argument, but to the unanswerable test of facts.
For this optional fertilization, determining the sex, the mother’s organism requires a seminal reservoir which distils its drop of sperm upon the egg contained in the oviduct and thus gives it a feminine character, or else leaves it its original character, the male character, by refusing it that baptism. This reservoir exists in the Hive-bee. Do we find a similar organ in the other Hymenoptera, whether honey-gatherers or hunters? The anatomical treatises are either silent on this point or, without further enquiry, apply to the order as a whole the data provided by the Hive-bee, however much she differs from the mass of Hymenoptera owing to her social habits, her sterile workers and especially her tremendous fertility, extending over so long a period.
I at first doubted the universal presence of this spermatic receptacle, having failed to find it under my scalpel in my former investigations into the anatomy of the Sphex-wasps and some other game-hunters. But this organ is so delicate and so small that it very easily escapes the eye, especially when our attention is not specially directed in search of it; and, even when we are looking for it and it only, we do not always succeed in discovering it. We have to find a globule attaining in many cases hardly as much as a millimetre (About one-fiftieth of an inch.–Translator’s Note.) in diameter, a globule headed amidst a tangle of air-ducts and fatty patches, of which it shares the colour, a dull white. Then again, the merest slip of the forceps is enough to destroy it. My first investigations, therefore, which concerned the reproductive apparatus as a whole, might very well have allowed it to pass unperceived.
In order to know the rights of the matter once and for all, as the anatomical treatises taught me nothing, I once more fixed my microscope on its stand and rearranged my old dissecting-tank, an ordinary tumbler with a cork disk covered with black satin. This time, not without a certain strain on my eyes, which are already growing tired, I succeeded in finding the said organ in the Bembex- wasps, the Halicti (Cf. Chapters 12 to 14 of the present volume.– Translator’s Note.), the Carpenter-bees, the Bumble-bees, the Andrenae (A species of Burrowing Bees.–Translator’s Note.) and the Megachiles. (Or Leaf-cutting Bees. Cf. Chapter 8 of the present volume.–Translator’s Note.) I failed in the case of the Osmiae, the Chalicodomae and the Anthophorae. Is the organ really absent? Or was there want of skill on my part? I lean towards want of skill and admit that all the game-hunting and honey-gathering Hymenoptera possess a seminal receptacle, which can be recognized by its contents, a quantity of spiral spermatozoids whirling and twisting on the slide of the microscope.
This organ once accepted, the German theory becomes applicable to all the Bees and all the Wasps. When copulating, the female receives the seminal fluid and holds it stored in her receptacle. From that moment, the two procreating elements are present in the mother at one and the same time: the female element, the ovule; and the male element, the spermatozoid. At the egg-layer’s will, the receptacle bestows a tiny drop of its contents upon the matured ovule, when it reaches the oviduct, and you have a female egg; or else it withholds its spermatozoids and you have an egg that remains male, as it was at first. I readily admit it: the theory is very simple, lucid and seductive. But is it correct? That is another question.
One might begin by reproaching it with making a singular exception to one of the most general rules. Which of us, casting his eyes over the whole zoological progression, would dare to assert that the egg is originally male and that it becomes female by fertilization? Do not the two sexes both call for the assistance of the fertilizing element? If there be one undoubted truth, it is certainly that. We are, it is true, told very curious things about the Hive-bee. I will not discuss them: this Bee stands too far outside the ordinary limits; and then the facts asserted are far from being accepted by everybody. But the non-social Bees and the predatory insects have nothing special about their laying. Then why should they escape the common rule, which requires that every living creature, male as well as female, should come from a fertilized ovule? In its most solemn act, that of procreation, life is one and uniform; what it does here it does there and there and everywhere. What! The sporule of a scrap of moss requires an antherozoid before it is fit to germinate; and the ovule of a Scolia, that proud huntress, can dispense with the equivalent in order to hatch and produce a male? These new-fangled theories seem to me to have very little value.
One might also bring forward the case of the Three-pronged Osmia, who distributes the two sexes without any order in the hollow of her reed. What singular whim is the mother obeying when, without decisive motive, she opens her seminal phial at haphazard to anoint a female egg, or else keeps it closed, also at haphazard, to allow a male egg to pass unfertilized? I could imagine impregnation being given or withheld for periods of some duration; but I cannot understand impregnation and non-impregnation following upon each other anyhow, in any sort of order, or rather with no order it all. The mother has just fertilized an egg. Why should she refuse to fertilize the next, when neither the provisions nor the lodgings differ in the smallest respect from the previous provisions and lodgings? These capricious alternations, so unreasonable and so exceedingly erratic, are scarcely appropriate to an act of such importance.
But I promised not to argue and I find myself arguing. My reasoning is too fine for dull wits. I will pass on and come to the brutal fact, the real sledge-hammer blow.
Towards the end of the Bee’s operations, in the first week of June, the last acts of the Three-horned Osmia become so exceptionally interesting that I made her the object of redoubled observation. The swarm at this time is greatly reduced in numbers. I have still some thirty laggards, who continue very busy, though their work is in vain. I see some very conscientiously stopping up the entrance to a tube or a Snail-shell in which they have laid nothing at all. Others are closing the home after only building a few partitions, or even mere attempts at partitions. Some are placing at the back of a new gallery a pinch of pollen which will benefit nobody and then shutting up the house with an earthen stopper as thick, as carefully made as though the safety of a family depended on it. Born a worker, the Osmia must die working. When her ovaries are exhausted, she spends the remainder of her strength on useless works: partitions, plugs, pollen-heaps, all destined to be left unemployed. The little animal machine cannot bring itself to be inactive even when there is nothing more to be done. It goes on working so that its last vibrations of energy may be used up in fruitless labour. I commend these aberrations to the staunch supporters of reasoning-powers in the animal.
Before coming to these useless tasks, my laggards have laid their last eggs, of which I know the exact cells, the exact dates. These eggs, as far as the microscopes can tell, differ in no respect from the others, the older ones. They have the same dimensions, the same shape, the same glossiness, the same look of freshness. Nor are their provisions in any way peculiar, being very well suited to the males, who conclude the laying. And yet these last eggs do not hatch: they wrinkle, fade and wither on the pile of food. In one case, I count three or four sterile eggs among the last lot laid; in another, I find two or only one. Elsewhere in the swarm, fertile eggs have been laid right up to the end.
Those sterile eggs, stricken with death at the moment of their birth, are too numerous to be ignored. Why do they not hatch like the other eggs, which outwardly they resemble in every respect? They have received the same attention from the mother and the same portion of food. The searching microscope shows me nothing in them to explain the fatal ending.
To the unprejudiced mind, the answer is obvious. Those eggs do not hatch because they have not been fertilized. Any animal or vegetable egg that had not received the life-giving impregnation would perish in the same way. No other answer is possible. It is no use talking of the distant period of the laying: eggs of the same period laid by other mothers, eggs of the same date and likewise the final ones of a laying, are perfectly fertile. Once more, they do not hatch because they were not fertilized.
And why were they not fertilized? Because the seminal receptacle, so tiny, so difficult to see that it sometimes escaped me despite all my scrutiny, had exhausted its contents. The mothers in whom this receptacle retained a remnant of sperm to the end had their last eggs as fertile as the first; the others, whose seminal reservoir was exhausted too soon, had their last-born stricken with death. All this seems to me as clear as daylight.
If the unfertilized eggs perish without hatching, those which hatch and produce males are therefore fertilized; and the German theory falls to the ground.
Then what explanation shall I give of the wonderful facts which I have set forth? Why, none, absolutely none. I do not explain facts, I relate them. Growing daily more sceptical of the interpretations suggested to me and more hesitating as to those which I may have to suggest myself, the more I observe and experiment, the more clearly I see rising out of the black mists of possibility an enormous note of interrogation.
Dear insects, my study of you has sustained me and continues to sustain me in my heaviest trials. I must take leave of you for to-day. The ranks are thinning around me and the long hopes have fled. Shall I be able to speak to you again? (This is the closing paragraph of Volume 3 of the “Souvenirs entomologiques,” of which the author has lived to publish seven more volumes, containing over 2,500 pages and nearly 850,000 words.–Translator’s Note.)
CHAPTER 6. INSTINCT AND DISCERNMENT.
The Pelopaeus (A Mason-wasp forming the subject of essays which have not yet been published in English.–Translator’s Note.) gives us a very poor idea of her intellect when she plasters up the spot in the wall where the nest which I have removed used to stand, when she persists in cramming her cell with Spiders for the benefit of an egg no longer there and when she dutifully closes a cell which my forceps has left empty, extracting alike germ and provisions. The Mason-bees (Cf. “The Mason-bees”: chapter 7.–Translator’s Note.), the caterpillar of the Great Peacock Moth (Cf. “Social Life in the Insect World” by J.H. Fabre, translated by Bernard Miall: chapter 14.– Translator’s Note.) and many others, when subjected to similar tests, are guilty of the same illogical behaviour: they continue, in the normal order, their series of industrious actions, though an accident has now rendered them all useless. Just like millstones unable to cease revolving though there be no corn left to grind, let them once be given the compelling power and they will continue to perform their task despite its futility. Are they then machines? Far be it from me to think anything so foolish.
It is impossible to make definite progress on the shifting sands of contradictory facts: each step in our interpretation may find us embogged. And yet these facts speak so loudly that I do not hesitate to translate their evidence as I understand it. In insect mentality, we have to distinguish two very different domains. One of these is INSTINCT properly so called, the unconscious impulse that presides over the most wonderful part of what the creature achieves. Where experience and imitation are of absolutely no avail, instinct lays down its inflexible law. It is instinct and instinct alone that makes the mother build for a family which she will never see; that counsels the storing of provisions for the unknown offspring; that directs the sting towards the nerve-centres of the prey and skilfully paralyses it, so that the game may keep good; that instigates, in fine, a host of actions wherein shrewd reason and consummate science would have their part, were the creature acting through discernment.
This faculty is perfect of its kind from the outset, otherwise the insect would have no posterity. Time adds nothing to it and takes nothing from it. Such as it was for a definite species, such it is to-day and such it will remain, perhaps the most settled zoological characteristic of them all. It is not free nor conscious in its practice, any more than is the faculty of the stomach for digestion or that of the heart for pulsation. The phases of its operations are predetermined, necessarily entailed one by another; they suggest a system of clock-work wherein one wheel set in motion brings about the movement of the next. This is the mechanical side of the insect, the fatum, the only thing which is able to explain the monstrous illogicality of a Pelopaeus when misled by my artifices. Is the Lamb when it first grips the teat a free and conscious agent, capable of improvement in its difficult art of taking nourishment? The insect is no more capable of improvement in its art, more difficult still, of giving nourishment.
But, with its hide-bound science ignorant of itself, pure insect, if it stood alone, would leave the insect unarmed in the perpetual conflict of circumstances. No two moments in time are identical; though the background remain the same, the details change; the unexpected rises on every side. In this bewildering confusion, a guide is needed to seek, accept, refuse and select; to show preference for this and indifference to that; to turn to account, in short, anything useful that occasion may offer. This guide the insect undoubtedly possesses, to a very manifest degree. It is the second province of its mentality. Here it is conscious and capable of improvement by experience. I dare not speak of this rudimentary faculty as intelligence, which is too exalted a title: I will call it DISCERNMENT. The insect, in exercising its highest gifts, discerns, differentiates between one thing and another, within the sphere of its business, of course; and that is about all.
As long as we confound acts of pure instinct and acts of discernment under the same head, we shall fall back into those endless discussions which embitter controversy without bringing us one step nearer to the solution of the problem. Is the insect conscious of what it does? Yes and no. No, if its action is in the province of instinct; yes, if the action is in that of discernment. Are the habits of an insect capable of modification? No, decidedly not, if the habit in question belongs to the province of instinct; yes, if it belongs to that of discernment. Let us state this fundamental distinction more precisely by the aid of a few examples.
The Pelopaeus builds her cells with earth already softened, with mud. Here we have instinct, the unalterable characteristic of the worker. She has always built in this way and always will. The passing ages will never teach her, neither the struggle for life nor the law of selection will ever induce her to imitate the Mason-bee and collect dry dust for her mortar. This mud nest needs a shelter against the rain. The hiding-place under a stone suffices at first. But should she find something better, the potter takes possession of that something better and instals herself in the home of man. (The Pelopaeus builds in the fire-places of houses.–Translator’s Note.) There we have discernment, the source of some sort of capacity for improvement.
The Pelopaeus supplies her larvae with provisions in the form of Spiders. There you have instinct. The climate, the longitude or latitude, the changing seasons, the abundance or scarcity of game introduce no modification into this diet, though the larva shows itself satisfied with other fare provided by myself. Its forebears were brought up on Spiders; their descendants consumed similar food; and their posterity again will know no other. Not a single circumstance, however favourable, will ever persuade the Pelopaeus that young Crickets, for instance, are as good as Spiders and that her family would accept them gladly. Instinct binds her down to the national diet.
But, should the Epeira (The Weaving or Garden Spider. Cf. “The Life of the Spider” by J. Henri Fabre translated by Alexander Teixeira de Mattos; chapters 9 to 14 and appendix.–Translator’s Note.), the favourite prey, be lacking, must the Pelopaeus therefore give up foraging? She will stock her warehouses all the same, because any Spider suits her. There you have discernment, whose elasticity makes up, in certain circumstances, for the too-great rigidity of instinct. Amid the innumerable variety of game, the huntress is able to discern between what is Spider and what is not; and, in this way, she is always prepared to supply her family, without quitting the domain of her instinct.
The Hairy Ammophila gives her larva a single caterpillar, a large one, paralysed by as many pricks of her sting as it has nervous centres in its thorax and abdomen. Her surgical skill in subduing the monster is instinct displayed in a form which makes short work of any inclination to see in it an acquired habit. In an art that can leave no one to practise it in the future unless that one be perfect at the outset, of what avail are happy chances, atavistic tendencies, the mellowing hand of time? But the grey caterpillar, sacrificed one day, may be succeeded on another day by a green, yellow or striped caterpillar. There you have discernment, which is quite capable of recognizing the regulation prey under very diverse garbs.
The Megachiles build their honey-jars with disks cut out of leaves; certain Anthidia make felted cotton wallets; others fashion pots out of resin. There you have instinct. Will any rash mind ever conceive the singular idea that the Leaf-cutter might very well have started working in cotton, that the cotton-wool-worker once thought or will one day think of cutting disks out of the leaves of the lilac- and the rose-tree, that the resin-kneader began with clay? Who would dare to indulge in any such theories? Each Bee has her art, her medium, to