CHAP. II. OF THE EGGS, LARVÆ, AND PUPÆ OF ANTS.

The exterior of ant-hills, their form and construction, have hitherto entirely occupied us: it was, however, necessary to commence by establishing the ants in their abode previous to describing the rest of their labours. The object which will now evidently create some interest, is that solicitude the workers evince for the object of their charge, and the maternal attention they bestow upon them from the period of their quitting the egg to that of their complete developement.⁠[1] Although several naturalists have studied the metamorphosis of ants, and described the principal circumstances connected with it, yet we are about to examine, under new relations, the developement and education of these insects in their different states. The history of the egg had entirely escaped their researches, as well as several particulars in the history of the pupæ and larvæ.

My predecessors, not having made use of a glazed apparatus to observe what passed in the interior of ant-hills, had but very rarely seen these insects engaged in their household occupations; and this was not so easy of accomplishment as it at first appeared.

These insects, although possessing so little timidity, and regardless, as it concerns themselves, of the several changes in the weather, evince the greatest concern for their little ones. For beings, so delicately formed, they dread the slightest variations of the atmosphere, are alarmed at the least danger which threatens them, and seem particularly anxious to withdraw them from our notice.

I was in my first attempts continually disappointed, from the great repugnance they manifested in allowing the light to penetrate their abode: whenever I attempted to glaze their apartments, or to lay open to view any of their halls or passages, if they did not completely abandon them, they at least prevented me from following them in their in-door labours. At one time they would darken, by a heap of different materials, all the halls which admitted the light; at another time, as if conscious that the glass, notwithstanding its transparency, could guard them from the external air, and that nothing was wanting to render it a true wall, but the power of excluding that glaring light, at all times so disagreeable to them, they preserved entire all the galleries contiguous to it, taking the sole precaution of covering it over with a layer of moistened earth, which effectually hindered further observation.

Thus disappointed, I employed a method more simple, though more effectual:—I removed a portion of the ant-hill, and then placed over the remainder a thin flat board inclined to the south; the ants, attracted by the heat brought their little ones to this place. By removing this outside shutter or contrevent, I could ascertain the progress in their growth, although the workers, on being disturbed, hastened to convey them to their under-ground quarters.

I was often obliged to vary the means I employed; for the ants, soon wearied by my visits, still baffled all my efforts, by making a true wall of earth behind the contrevent. After having for some time attended to the manners and habits of these insects, I found that we might accustom them by degrees to suffer the entrance of the light in their abode; but it was necessary, notwithstanding, to use much caution. What succeeded with me the best, was that of forming an oblong opening in the middle of a table, and affixing underneath, a double frame, glazed on its two longest sides, and opened only at the upper part, which communicated with this aperture. These frames (fig. 1. Pl. I.) being furnished with shutters, permitted me, either to observe the ants, or to favour them in their taste for obscurity. This done, I scattered all the materials of a nest of Fallow Ants upon the table, and left them at liberty to arrange them at the bottom of the glazed box, which they did in such a manner, that it was easy to observe all their galleries, and the apartments to which they led. I at length covered over the whole of the materials with a large bell-glass, in order that I might witness the movements of my prisoners, as well inside as on the outside, and at the same time guard against their escape. But when I saw they were accustomed to their fate, and did not seek to leave their prison, I allowed them free issue from under the bell-glass, and the liberty of running over the platform upon which it rested, taking only the precaution of plunging the feet of the table in vessels filled with water, to arrest the ants in their passage, should they attempt to escape.

This apparatus, and several others of which the explanation would be long and tedious, had all the success I wished. I observed, with much pleasure, that the ants continued to take care of the larvæ, which proved, that in taking them, in some respects, from the state of nature, I had not too much disturbed them. This gave me reason to hope, that I should observe, in its greatest extent, all the care they took of the rising generation.

I did not, however, always keep to these artificial means. I compared, as often as possible, the conduct of my prisoners, with that of those ants inhabiting and ranging about the fields, and as I never remarked any sensible difference in their manner of acting, I concluded I could trust the results obtained by means of my glazed apparatus.

Let us now open the shutter which conceals from us the interior of the ant-hill, and let us see what is passing there.

Here, the pupæ are heaped up by hundreds in their spacious lodges; there, the larvæ are collected together, and guarded by workers. In one place, we observe an assemblage of eggs, in another place, some of the workers seem occupied in following an ant of a larger size than the rest;—this is the mother, or at least one of the females, for there are always several in each ant-hill:—she lays as she walks, and the guardians, by whom she is surrounded, take up her eggs, or seize them at the very moment of her laying them; they collect them together, and carry them in little heaps in their mouths.⁠[2] On looking a little closer, we find that they turn them continually with their tongues; it even appears, they pass them one after the other between their teeth, and thus keep them constantly moistened. Such is the first aperçu which my glazed apparatus offered.

Having directed my close attention to these eggs, I remarked they were of different sizes, shades, and forms. The smallest were white, opake, and cylindrical; the largest, transparent, and slightly arched at both ends; those of a middle size were semi-transparent. In holding them up to the light, I observed a sort of white oblong cloud; in some, a transparent point might be remarked at the superior extremity; in others, a clear zone above and underneath the little cloud. The largest presented a single opake and whitish point in their interior. There were some whose whole body was so remarkably clear, as to allow of my observing very distinctly the rings. In fixing my attention more closely upon the latter, I observed the egg open, and the larva appear in its place.

Having compared these eggs with those just laid, I constantly found the latter of a milky whiteness, completely opake, and smaller by one-half; so that I had no reason to doubt of the eggs of ants receiving a very considerable increase in size; that in elongating, they become transparent, but do not at this time disclose the form of the worm which is always arched.

To be convinced of the truth of this statement, I viewed these eggs with the microscope; I also measured them, and having separated them from each other, found the longest to be those only in which the worms were disclosed in my presence. If I removed them from the workers, before they had attained their full length and transparency, they dried up, and the worms never quitted them.

Is it, then, to the care which the workers take in passing them across their mouths, that we must attribute the secret of their preservation? Do these eggs require this humidity, or do they absorb a part of it, to furnish nourishment to the little worms they contain? It appears at least highly probable; and the observations of M. Reaumur give weight to this opinion. I have discovered in his writings, that there are other eggs, which also increase in size,—as those lodged in the galls of different trees, which are occasioned by Cynips⁠[3]⁠, or other insects of the same kind.

“It ought not,” says this exact and judicious observer, “to be passed by in silence, that the egg which I found in the gall appeared to me considerably larger than the eggs of the same species, when they proceed from the body of the fly, or even when they are taken from the body of the impregnated or mother-fly, near the time of their being laid. The whole of those I took from the abdomen of the flies I killed were remarkably small; it therefore appeared certain, that the egg would have increased, and indeed had increased, in the gall.”

We are only in the habit of observing eggs surrounded by a covering incapable of extension; but why is it that those eggs, which nature has enclosed, in a flexible membrane, do not increase? The envelope of the egg may, in this instance, be compared to the membrane which includes the human fœtus, and those of quadrupeds.

Nature has formed the eggs of some other insects in such a manner, that they are also capable of increase: such are, according to M. Vallisnieri, the eggs of the Tenthredo, which produce those larvæ that feed upon the rose.⁠[4]⁠

These remarkable examples authorise me in admitting an increase in size, in the eggs of ants, as fully proved; although it may not be exactly under the same circumstances as those of which the philosopher I have just quoted speaks; but if they are not surrounded with a liquid, or preserved from the influence of the external air, their pellicle, moistened every instant by the workers, may preserve a certain degree of suppleness, and the faculty of extension, according to the developement of the worm they enclose.

At the end of fifteen days, the little worm is seen to quit the shell: its body is then perfectly transparent, and presents only a head and rings, without any rudiment of feet or antennæ. The insect, at this period, is completely dependant upon the workers.

I have been enabled to observe, through the glasses of my artificial ant-hill, the great care taken of these little worms, which bear also the name of Larvæ. They were generally guarded by a body of ants, who, raised upon their feet, with their abdomen brought between these members, were prepared to cast their venom upon all intruders, whilst, here and there, other workers were engaged in clearing the passages, by removing the materials which were out of place; a great number of their companions taking at the same time their repose, and appearing to be fast asleep: but a busy scene occurred at the moment of transporting their little ones to enjoy the warmth of the sun. When the sun’s rays fell upon the exterior portion of the nest, the ants, who were then on the surface, descended with great rapidity to the bottom of the ant-hill, struck with their antennæ the other ants, ran one after the other, and jostled their companions, who mounted at the moment under the bell-glass, and redescended with the same speed, putting in their turn the whole colony in motion, so that we could observe a swarm of workers, filling up all the passages; but what proved still more their intention by these movements, was, the violence with which the workers sometimes seized, with their mandibles, those who did not appear to understand them, dragging them forth to the top of the ant-hill, and immediately leaving them, to go and seek those still remaining with the young.

As soon as the ants had intimation of the appearance of the Sun, they occupied themselves with the larvæ and pupæ; they carried them with all expedition above the ant-hill, where they left them exposed to the influence of the heat. Their ardour suffered no relaxation; the female larvæ (which are heavier, and much larger than those of the other cast) were carried, with some difficulty, through the narrow passages, leading from the interior to the exterior of the ant-hill, and placed in the sun, by the side of those of the workers and males. After remaining there a quarter of an hour, the ants again took them up, and sheltered them from the direct rays of the sun, by placing them in chambers, situated under a layer of straw, which did not entirely intercept the heat.

The workers, after having fulfilled the duties imposed upon them in regard to the larvæ, did not forget themselves; they sought, in their turn, to stretch themselves in the sun, lay upon each other in heaps, and seemed to enjoy some repose, but it was of no long duration. I observed a great number constantly employed on the surface of the ant-hill, and others engaged in carrying back the larvæ, in proportion as the sun declined. The moment of nourishing them being at length arrived, each ant approached a larva, and offered it food. “The larvæ of ants,” observes M. Latreille, “resemble, when they quit the egg, little white worms, destitute of feet, thick, short, and in form almost conical; their body is composed of twelve rings; the anterior part is slender and curved. We remark at the head two little horny pieces or hooks, too distant from each other to be regarded as true teeth; under these hooks we observe four little points or cils, two on each side, and a mamelon, or tubercular process, almost cylindrical, soft, and retractile, by which the larva receives its food.”⁠[5]⁠

The ants do not prepare for their larvæ provisions de bouche, as happens with several species of bees and other insects, which provide before-hand for the wants of their little ones; they give them every day the nourishment best suited to their condition; the instinct of the larvæ is sufficiently developed, to enable them to demand and receive their repast, in the same way as the young of birds receive it from their parents. When hungry, they erect their body, and search with their mouth that of the workers, who are appointed to nourish them. The ant then separates its mandibles, and allows them to take from its very mouth the fluids they seek.

I know not if these fluids undergo any change in the body of the workers, but I am far from believing it to be the case, since I have often seen the ants offer them nourishment, almost immediately after they had themselves taken it; perhaps honey and sugar dissolved in water. I presume, however, that the regimen is proportioned to the age and sex of each individual, that the aliment is more substantial the nearer the time of their metamorphosis, and that more is given to the larvæ of females than to those of the workers and males; but the questions which have reference to the quality and quantity of these aliments are of difficult solution: however, as it is of some importance to ascertain if the nourishment which the larva takes has any influence upon the development of the sexes in the females of ants, as obtains in bees, I purpose making some experiments by nourishing myself the larvæ of different species. Let us at present follow the workers in the last care they bestow upon the larvæ; it is not sufficient to lay them in the sun and give them food; it is still necessary to keep them remarkably clean. These insects, therefore, who in point of tenderness to the young committed to their charge, do not yield to any of the females of the larger animals, pass their tongue and mandibles continually over their bodies, and thus render them perfectly white.⁠[6] The ants have also another occupation; that of extricating them from their cuticle, which becomes distended and soft at the period of their transformation.

Previous to changing this skin, the larvæ spin themselves a silken covering or cocoon, (as is the case with many other insects,) in which in the form of pupæ, they prepare to undergo their last metamorphosis. This cocoon is of a cylindrical form, elongated, of a pale yellow colour, and very smooth and close in its texture. A remarkable circumstance for which no cause has been yet assigned is, that there are ants whose larvæ never spin; but this exception only holds with those species that possess a sting and two knots on the peduncle of the abdomen. Thus, there are some larvæ which undergo their change in a silken envelope, and others which become pupæ, without lying under the necessity of spinning or weaving one.⁠[7]⁠

The larvæ of some ants pass the winter heaped up in the lowermost floor of their dwelling. I have found, at this period, very small larvæ in the nests inhabited by the Yellow Ant, the Field Ant, and some other species, but none, in those of the Fallow, Ash-coloured, and Mining Ants. Those that are to pass the winter in this state are covered with hair, which is not the case in summer; affording another proof of that Providence at which naturalists are struck at every step. We do not find the larvæ of males and females but in the spring; their transformation takes place in the beginning of summer.

The insect, in the state of pupa, has acquired the figure it will always preserve; nothing seems wanting but strength and a little more consistence: it is also as large as it will ever be; all its members are distinct, one single pellicle envelopes them. The ant, under this form, continues to move for some moments after its quitting the state of larva, but it soon becomes immoveable: it afterwards changes gradually in colour, passing from a fine white to a pale yellow; then becoming red, and in several species, brown, almost verging to black. The rudiments of wings may at this time be seen in those which are destined to fly. The pupæ have still many attentions to receive from the workers; the greater part are enclosed in a tissue spun by themselves before their metamorphosis; but they cannot, like other insects, liberate themselves from this covering by effecting an opening in it with their teeth. They have scarcely the power of moving; their covering is of too compact a texture, and formed of too strong a silk, to allow of their tearing it without the assistance of the workers. But how do these indefatigable attendants ascertain the proper moment for this process?—If they possessed the faculty of hearing, we might imagine they knew the fit time, from some noise produced in the interior of the prison by the insects whose developement has commenced; but there is no indication favouring this opinion; it is probable they have a knowledge of it from some slight movements that take place within, which they ascertain through the medium of their antennæ; for these organs are endowed with a sensibility, of which it would be difficult to form a just idea: whatever it be, they are never deceived.

Let us still follow them in that labour, wherein are displayed, as it regards their charge, a zeal and an attachment which would justly merit our attention, even were they the real parents of these insects; how much greater then must be our astonishment, when we consider that they bear no further relation to them, than that of being born under the same roof. Several males and females lay in their enveloping membrane in one of the largest cavities of my glazed ant-hill. The Labourers, assembled together, appeared to be in continual motion around them. I noticed three or four mounted upon one of these cocoons, endeavouring to open it with their teeth at that extremity answering to the head of the pupa; they began thinning it, by tearing away some threads of silk where they wished to pierce it; and at length, by dint of pinching and biting this tissue, so extremely difficult to break, they formed in it a vast number of apertures. They afterwards attempted to enlarge these openings, by tearing or drawing away the silk; but these efforts proving ineffectual, they passed one of their teeth into the cocoon, through the apertures they had formed, and by cutting each thread, one after the other, with great patience, at length effected a passage, of a line in diameter, in the superior part of the web. They now uncovered the head and feet of the insect to which they were desirous of giving liberty, but before they could release it, it was absolutely necessary to enlarge the opening; for this purpose, these guardians cut out a portion in the longitudinal direction of the cocoon, with their teeth alone, employing these instruments as we are in the habit of employing a pair of scissars. A considerable degree of agitation prevailed in this part of the ant-hill; a number of ants were occupied in disengaging the winged individual of its envelope; they took repose and relieved each other by turns, evincing great eagerness in seconding their companions in this undertaking.⁠[8] To effect its speedy liberation, some raised up the portion or bandalette cut out in the length of the cocoon; whilst others drew it gently from its imprisonment. When the ant was extricated from its enveloping membrane, it was not, like other insects, capable of enjoying its freedom, and taking flight: nature did not will it that it should so soon be independent of the labourers. It could neither fly, nor walk, nor without difficulty stand; for the body was still confined by another membrane, from which it could not, by its own exertions, disengage itself.

In this fresh embarrassment, the labourers did not forsake it; they removed the satin-like pellicle which embraced every part of the body, drew the antennæ gently from their investment, then disengaged the feet and the wings, and lastly, the body, the abdomen, and its peduncle. The insect was now in a condition to walk and receive nourishment, for which it appeared there was urgent need. The first attention therefore, paid it by the guardians, was that of giving it the food I had placed within their reach.

The ants in every part of the ant-hill were occupied in giving liberty to the males, females, and young labourers, that were still enveloped. On being dispossessed of their coverings, the remnants were collected and placed aside in one of the most distant lodges of their habitation; for these insects observe the greatest order and regularity. Some species of ants remove these shreds to a distance from the ant-hill, others, cover the exterior surface of their nest with them, or collect them in particular apartments.⁠[9]⁠

The labourers we have seen in charge of the larvæ and pupæ evince the same solicitude for the ants, freshly transformed: they lie for some days under the necessity of watching and following them; they accompany them in their excursions, point out to them the paths and labyrinths of their habitation, and nourish them with the greatest care; they also perform the difficult task of extending the wings of the males and females, which would otherwise remain folded up, and acquit themselves with such address, as not to injure these frail and delicate members.

At one time, they bring together, in the same apartments, the males they find rambling; at another time, act as guides in conducting them from the ant-hill. In short, the labourers appear to have the complete direction of their conduct, as long as they remain there, and neglect not to discharge the several duties, connected with these insects (whose strength is not yet developed) until the period of their taking flight for the purpose of continuing their kind.

How can we sufficiently admire the assiduity which the labouring ants evince for the little ones whose safety is confided to them!—By what bond has nature attached them so strongly to the progeny of another mother! This question having a reference to the different families composed of three sorts of individuals,—the labourers, charged with educating the young, fabricating, and provisioning the nest; and those upon whom the office devolves of multiplying the species,—deserves to be treated at greater length, and with greater attention, than our confined knowledge permits. But we have a glimpse, however, of the secret of this singular constitution, in the resemblance the labourers have with the female ants, relatively to their external sexual organs. The connexion which exists between ants, and hive and humble bees, throws additional light upon this subject, by showing us labourers demi-fecund with the one⁠[10]⁠, and little rival females, abundant enough with the other.⁠[11] That solicitude also which the labouring ants evince for the larvæ, whose birth they have witnessed, clearly discovers their sex, and would be sufficient to prove that they are neither neuters nor males, even if the conduct of the males towards them did not indicate that they belong to the class of females. This observation, which I have several times made, (the details of which I suppress,) leaves me in no doubt upon this point. I shall here only add, that I have never known the labouring ants produce eggs, and have constantly found the approach of the male attended with the sacrifice of their lives.

But with what view does nature permit as many sterile females among ants as among wasps and bees? Is it not in order to increase the number of individuals, in the same family, without producing a population that would be more than proportioned to it?—In reserving a certain number of females for conception, she has appointed others to take care of the infant generation. She has even deprived the latter of the faculty of flying; but in return for this, they enjoy a sweet recompense, either (as we have no reason to doubt) by their being inspired for their charge with the sentiments of mothers for their young, or by their having an unlimited power over the other orders of the society in which they live; a truth which I hope to establish in the course of this work, and which differs widely from the received opinion, that these republics are governed by several chiefs.