An American species of the same genus, C. pennsylvanicus, the carpenter-ant, establishes its nests in the stumps of trees. Leidy observed that solitary females constructed for themselves cells in the wood and closed the entrances, and that each one in its solitary confinement reared a small brood of larvae. The first young produced in this case are said to be of the dwarf caste, and it was thought by the observer that the ant remained not only without assistance but also without food during a period of some weeks, and this although she was herself giving food to the larvae she was rearing.
Adlerz states that the females or young queens take no food while engaged in doing their early work, and that the large quantity of fat-body they possess enables them to undergo several months of hunger. In order to feed the young larvae they use their own eggs or even the younger larvae. It is to the small quantity of food rather than to its nature that he attributes the small size of the first brood of perfect workers. M. Janet[[63]] has recently designed an ingenious and simple apparatus for keeping ants in captivity. In one of these he placed a solitary female of Lasius alienus, unaccompanied by any workers or other assistants, and he found at the end of 98 days that she was taking care of a progeny consisting of 50 eggs, 2 larvae, 5 pupae in cocoons, 5 without cocoons. On the 102nd day workers began to emerge from the cocoons.[[64]] From these observations it is evident that the queen-ant, when she begins her nest, lives under conditions extremely different from those of the royal state she afterwards reaches.
In many kinds of ants the full-grown individuals are known to feed not only the larvae by disgorging food from their own mouths into those of the little grubs, but also to feed one another. This has been repeatedly observed, and Forel made the fact the subject of experiment in the case of Camponotus ligniperdus. He took some specimens and shut them up without food for several days, and thereafter supplied some of them with honey, stained with Prussian blue; being very hungry, they fed so greedily on this that in a few hours their hind bodies were distended to three times their previous size. He then took one of these gorged individuals and placed it amongst those that had not been fed. The replete ant was at once explored by the touches of the other ants and surrounded, and food was begged from it. It responded to the demands by feeding copiously a small specimen from its mouth: when this little one had received a good supply, it in turn communicated some thereof to other specimens, while the original well-fed one also supplied others, and thus the food was speedily distributed. This habit of receiving and giving food is of the greatest importance in the life-history of ants, and appears to be the basis of some of the associations that, as we shall subsequently see, are formed with ants by numerous other Insects.
Fig. 60—Oecophylla smaragdina. Worker using a larva for spinning.
Oecophylla smaragdina, a common ant in Eastern Asia, forms shelters on the leaves of trees by curling the edges of leaves and joining them together. In doing this it makes use of an expedient that would not be believed had it not been testified by several competent and independent witnesses. The perfect ant has no material with which to fasten together the edges it curls; its larva, however, possesses glands that secrete a supply of material for it to form a cocoon with, and the ants utilise the larvae to effect their purpose. Several of them combine to hold the foliage in the desired position, and while they do so, other ants come up, each one of which carries a larva in its jaws, applies the mouth of the larva to the parts where the cement is required, and makes it disgorge the sticky material. Our figure is taken from a specimen (for which we are indebted to Mr. E. E. Green) that was captured in the act of bearing a larva.
Formica rufa, the Red-ant, Wood-ant, or Hill-ant, is in this country one of the best-known members of the Formicidae. It frequents woods, especially such as are composed, in whole or part, of conifers, where it forms large mounds of small sticks, straws, portions of leaves, and similar material. Although at first sight such a nest may appear to be a chaotic agglomeration, yet examination reveals that it is arranged so as to leave many spaces, and is penetrated by galleries ramifying throughout its structure. These mound-nests attain a considerable size when the operations of the industrious creatures are not interfered with, or their work destroyed, as it too often is, by ignorant or mischievous persons. They may reach a height of three feet or near it, and a diameter of twice that extent. The galleries by which the heaps are penetrated lead down to the earth below. From the mounds extend in various directions paths constantly traversed by the indefatigable ants. M‘Cook observed such paths in the Trossachs; they proceed towards the objects aimed at in lines so straight that he considers they must be the result of some sense of direction possessed by the ants; as it is impossible to suppose they could perceive by the sense of sight the distant objects towards which the paths were directed: these objects in the case M‘Cook describes were oak-trees up which the ants ascended in search of Aphides.
M‘Cook further observed that one of the oak-trees was reached by individuals from another nest, and that each of the two parties was limited to its own side of the tree, sentinels being placed on the limits to prevent the trespassing of an intruder; he also noticed that the ants saw an object when the distance became reduced to about an inch and a half from them. This species is considered to be wanting in individual courage; but when acting in combination of vast numbers it does so with intelligence and success. It does not make slaves, but it has been observed by Bignell and others that it sometimes recruits its numbers by kidnapping individuals from other colonies of its own species. Its nests are inhabited by forty or fifty species of guests of various kinds, but chiefly Insects. Another ant, Myrmica laevinodis, sometimes lives with it in perfect harmony, and Formicoxenus nitidulus lives only with F. rufa. Amongst the most peculiar of its dependants we may mention large beetles of the genera Cetonia and Clythra, which in their larval state live in the hills of the wood-ant. It is probable that they subsist on some of the vegetable matter of which the mounds are formed. Adlerz has given some attention to the division of labour amongst the different forms of the workers of ants, and says that in F. rufa it is only the bigger workers that carry building and other materials, the smaller individuals being specially occupied in the discovery of honey-dew and other Aphid products. In Camponotus it would appear, on the other hand, that the big individuals leave the heavy work to be performed by their smaller fellows.
The wood-ant and its near allies have been, and indeed still are, a source of great difficulty to systematists on account of the variation that occurs in the same species, and because this differs according to locality. Our European F. rufa has been supposed to inhabit North America, and the interesting accounts published by M‘Cook of the mound-making ant of the Alleghanies were considered to refer to it. This Insect, however, is not F. rufa, as was supposed by M‘Cook, but F. exsectoides, Forel. It forms colonies of enormous extent, and including an almost incredible number of individuals. In one district of about fifty acres there was an Ant City containing no less than 1700 of these large ant-hills, each one teeming with life. It was found by transferring ants from one hill to another that no hostility whatever existed between the denizens of different hills; the specimens placed on a strange hill entered it without the least hesitation. Its habits differ in some particulars from those of its European congener; the North American Insect does not close the formicary at night, and the inquilines found in its nest are very different from those that live with F. rufa in Europe. Whether the typical wood-ant occurs in North America is doubtful, but there are races there that doubtless belong to the species.
F. sanguinea is very similar in appearance to its commoner congener F. rufa, and is the only slave-making ant we possess in Britain. This species constructs its galleries in banks, and is of very courageous character, carrying out its military operations with much tactical ability. It is perfectly able to live without the assistance of slaves, and very frequently does so; indeed it has been asserted that it is in our own islands (where, however, it is comparatively rare) less of a slave-owner than it is in Southern Europe, but this conclusion is very doubtful. It appears when fighting to be rather desirous of conquering its opponents by inspiring terror and making them aware of its superiority than by killing them; having gained a victory it will carry off the pupae from the nest it has conquered to its own abode, and the ants of the stranger-species that develop from these pupae serve the conquerors faithfully, and relieve them of much of their domestic duties. The species that F. sanguinea utilises in this way in England are F. fusca, F. cunicularia, and possibly Lasius flavus. Huber and Forel have given graphic accounts of the expeditions of this soldier-ant. In the mixed colonies of F. sanguinea and F. fusca the slaves do most of the house-work, and are more skilful at it than their masters. Adlerz says that one of the slaves will accomplish twice as much work of excavation in the same time as the slave-owner; these latter being lazy and fond of enjoyment, while the slaves are very industrious.