Sivut kuvina
PDF
ePub

ing to the species of the building-insect. Ants, on the contrary, are able to vary the forms of their nests according to circumstances and their own peculiar advantages, showing quite a genius for new combinations. In some hot countries there are nomad ants which make no nests, and form living balls on trees; but in Europe all the species of the social ants construct nests or abodes, whither they retire in winter, and where they often collect together in clusters. The most simple form of a nest is a burrow, which at first is a mere hole, whether in the ground or in the bark of a tree; these burrows may have both an entrance and exit hole. The nests of some species, on the other hand, show elaborate structure. M. Forel, in his interesting chapter on the architecture of nests, makes the following five great divisions :-1, nests of pure earth; 2, nests bored in wood; 3, nests of card-board, wood, or other material ; 4, nests of composite materials ; 5, abnormal nests. Each of these admits of several varieties of structure according to the habits and wants of the different species. Thus there are earth-nests of built-up domes, nests formed by undermining, nests under stones; nests in wood may be scooped out of the wood itself or the inner surface of the bark, portions of the solid parts being left for pillars and partitions, reminding one of the human worker in our coal and salt mines. Paper or card-board nests are very rare, there being only one European species which constructs this kind of nest, the Lasius fuliginosus Latreille. Nests formed of composite materials may consist of underground minings surmounted by a dome, or they may be formed with no dome-like superstructure in old decayed tree roots and trunks. The wood-ant, hill, or horseant (Formica rufa) of this country is a familiar example of the former kind of nest-builder, while the extremely common Myrmica scabrinodis may be frequently found in nests of the latter description. The hill or wood-ant is the largest of our British species; the ant-hill or dome-like exterior is only a portion of the nest; the materials of which it is composed consist of earth mixed with almost any transportable substances within reach, such as bits of grass, stalks, small dry twigs, the needle-like leaves of the larch, bits of dry leaves, &c.

M. Forel mentions the occurrence also of various bodies more or less spherical, as little stones and shells of small molluscs. Huber has detailed the formation of the nest of this species.

* To form an idea how the straw or stubble roof is formed, let us take a view of the ant-hill in its origin, where it is simply a cavity in the earth. Some of its future inhabitants are seen wandering about in search of materials fit for the exterior work, with which, though rather irregularly, they cover up the entrance; whilst others are employed in mixing the earth thrown up, in hollowing the interior with fragments of wood and leaves, which are every moment brought in by their fellow-assistants, and this gives a certain consistence to the edifice which increases in size daily. Our little architects leave here and there cavities where they intend constructing the galleries which are to lead to the exterior, and as they remove in the morning the barriers placed at the entrance of their nest the preceding evening, the passages are kept entire during the whole time of its construction; we soon observe it to become convex, but we should be greatly deceived did we consider it solid. This roof is destined to include many apartments or storeys. Having observed the motions of these little masons through a pane of glass which I adjusted against one of their habitations, I am enabled to speak with some degree of certainty of the manner in which they are constructed. It is by excavating or inining the under-portion of their edifice that they form their spacious halls, low, indeed, and of heavy construction, yet sufficiently convenient for the use to which they are appropriated—that of receiving at certain hours of the day the larvæ and pupæ. These halls have a free communication by galleries, made in the same manner. If the materials of which the ant-hill is composed were only interlaced, they would fall into a confused heap every time the ants attempted to bring them into regular order. This, however, is obviated by their tempering the earth with rain-water, which afterwards hardening in the sun, so completely and effectually binds together the several substances as to permit the removal of certain fragments from the ant-hill without any injury to the rest; it moreover strongly opposes the introduction of the rain. I never found, even after long and violent rains, the interior of the nest wetted to more than a quarter of an inch from the surface, provided it had not been previously out of repair or deserted by its inhabitants. The ants are extremely well-sheltered in their chambers, the largest of which is placed nearly in the centre of the building ; it is much loftier than the rest and traversed only by the beams that support the ceiling; it is in this spot that all the galleries terminate, and this forms, for the most part, their usual residence. As to the underground portion, it can only be seen when the ant-hill is placed against a declivity; all the interior may then be readily brought in view by simply raising up the straw roof. The subterranean residence consists of a range of apartments excavated in the earth, taking an horizontal direction.'

M. Forel has drawn particular attention to small bits of grass-stems or of wood, thirteen centimetres long and i} milimetres in diameter, which the ants employ in forming their galleries; these are the beams which give support to the galleries and chamber; they are arranged cross-ways interlacing one another, and the interstices are filled up with rounded materials; these galleries admit of being constructed into walls in different parts of the nest, by the filling up of the interstices between the beams, thus separating the small chambers and forming distinct galleries.

According to Huber ants seem to be aware of the approach of rain. When the sky is cloudy in the morning, or rain is * indicated, the ants, who seem to be aware of it, open but in

part their several avenues, and immediately close them when the rain commences.'

We must not dwell longer on these interesting points connected with the architecture of these little builders, except to notice the paper-made nest of the fuliginous ant of Huber, the Lasius fuliginosus of more recent authorities. This species is one which excavates its abode in wood, and is the only paperbuilder amongst ants. The oak, the willow, and other trees are occupied by these small ants, and sometimes entirely hollowed out by them; the nest consists of numberless storeys, more or less horizontal, with floors and ceilings five or six lines distant from each other as thin as a playing card, supported by vertical partitions forming an infinity of chambers, or by a series of small slender columns, allowing one to see between them to the extent of an almost entire storey; the whole is composed of a blackish and as it were smoked colour.' By what means is the paper material manufactured by this ant ? Meinert thinks that it is composed of woody particles, and a substance secreted by certain mandibulary and metathoracic glands. M. Forel is inclined to agree with Meinert, but the ants which he kept in confinement and which he supplied with sawdust, refused to work with it under his observation. Leaving the nests themselves, let us notice their various inhabitants—such as eggs, larvæ, nymphæ, and the perfect insects—as the females, males, and neuters.

After the female has deposited some eggs they are taken up by the workers and deposited in little packets. The eggs increase in size after exclusion, and this growth it is supposed is occasioned by the very curious habit of the workers constantly licking them for about fifteen days, nourishment being supplied by a kind of endosmose or the transmission of some nutritious substance from without inwards through the walls

This curious fact of licking the eggs did not escape the notice of Huber, who witnessed it under one of his large bell-glasses. On looking a little closer,' he says, ' we ' find that they turn them continually with their tongues ; it 'even appears they pass them one after the other between their ' mandibles, and thus keep them constantly moistened.' The eggs are whitish or opaquely yellowish. Unlike bees, there is no appreciable difference between the eggs which produce females, males, workers, or soldiers ; the larva is a small white grub with a dozen indistinct rings, footless, and eyeless; in

of the egg

most cases the larvæ are incapable of any motion with the exception of the mouth, which opens freely for food. When hungry the little grub opens its mouth, and the workers approach and disgorge honied sweets in a liquid form therein. These grubs are utterly helpless, and the workers not only feed them, but caress them with licking, clean them and transport them from one part of the nest to another, that they may have the proper degree of temperature. The larve which are to develope into females have the same kind of food as those which will become males and workers; unlike the bees whose queen-larva requires a different diet from the worker-larva. Sometimes the workers carry off several larvæ, smaller ones adhering to larger ones; if a larva is by accident dropped, the worker does not recover its burden until it is touched with the antennæ.

The duration of life in the larva-state is, in some cases, long ; certain larvæ hatched in the autumn do not become nymphæ till July in the following year (Solenopis fugax); others appearing as eggs in April, become nymphæ about the end of May.

The nymphæ in some species are enclosed in cocoons, in others they are naked, but sometimes the same species has both kinds; they are always motionless and neither eat nor grow; the workers show as much anxious solicitude for the nymphæ as for the larvæ, cleaning and rubbing them, and transporting them from place to place as before. When a larva means to become an enclosed nympha, it fixes itself to the soil and spins a cocoon. Sometimes the nymphæ can release themselves from their coverings, the skin slitting longitudinally down the back by the lively movements of the inhabitants. M. Forel tells us that this self-liberation is not uncommon amongst the worker-nymphæ, but that the task is a more difficult one in the males and females, especially in the case of the former, when it rarely succeeds. The difficulty is caused by the large wings and abdomens of the two sexes; in such cases the aid of the workers is necessary. The help then given has been well described by Huber.

'Several males and females lay in their enveloping membrane in one of the largest cavities of my glazed ant-bill. 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 nympha. 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 the 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 scisgors. 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. 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 stand, without difficulty, 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 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.'

These facts recorded by Huber have been confirmed by Fenger and Forel.

The cast-off exuviæ of the cocoons are in some species removed by the workers, and heaped up around the gates of the nest, or they are carried away to a distance, or mixed with the materials of the nest. The first instinct exhibited in the young worker-ant is a maternal one; as soon as it has learnt to know where and what it is, which requires some days, the young pale-coloured worker exhibits the same care and anxiety for the yet unhatched cocoons as the elders. One important duty of the workers is to attend to the wings of the newly-born males and females, which they carefully extend and unfold; without this assistance the wings would remain folded up and useless for flight. Leaving the workers for a time, let us look at what takes place amongst the males and females. As amongst bees so amongst ants, the males are incapable of work, seem to lounge about the doors for some days, not knowing what

« EdellinenJatka »