The honey-ant of the United States and Mexico has been investigated by M‘Cook and others; the chief peculiarity of the species is that certain individuals are charged with a sort of honey till they become enormously distended, and in fact serve as leather bottles for the storage of the fluid. The species Myrmecocystus hortideorum and M. melliger, are moderate-sized Insects of subterranean habits, the entrance to the nest of M. hortideorum being placed in a small raised mound. The honey is the product of a small gall found on oak leaves, and is obtained by the worker-ants during nocturnal expeditions, from which they return much distended; they feed such workers left at home as may be hungry, and then apparently communicate the remainder of the sweet stuff they have brought back to already partly charged "honey-bearers" left in the nest. The details of the process have not been observed, but the result is that the abdomens of the bearers become distended to an enormous extent (Figs. 62, 63), and the creatures move but little, and remain suspended to the roof of a special chamber. It is considered by M‘Cook that these living honey-tubs preserve the food till a time when it is required for the purposes of feeding the community. The distension is produced entirely by the overcharging of the honey-crop, the other contents of the abdomen being forced by the distention to the posterior part of the body. Lubbock has since described an Australian ant, Melophorus inflatus, having a similar peculiar habit, but belonging to the allied tribe Plagiolepisii. Quite recently a South African honey-tub ant belonging to the distinct genus Plagiolepis (Ptrimeni For.) has been discovered, affording a proof that an extremely specialised habit may arise independently of relation between the Insects, and in very different parts of the world.
Species of the genus Lasius are amongst the most abundant of the ant-tribe in Britain. They are remarkable for their constructive powers. L. niger, the common little black garden-ant, forms extensive subterranean galleries, and is extremely successful in the cultivation of various forms of Aphidae, from the products of which the species derives a large part of its subsistence. The ants even transport the Aphidae to suitable situations, and thus increase their stock of this sugary kind of cattle, and are said to take the eggs into their own dwellings in the autumn so that these minute and fragile objects may be kept safe from the storms and rigours of winter. These little creatures are brave, but when attacked by other ants they defend themselves chiefly by staying in their extensive subterranean galleries, and blocking up and securing these against their assailants.
L. fuliginosus, another of our British species, has very different habits, preferring old trees and stumps for its habitation; in the hollows of these it forms dwellings of a sort of card; this it makes from the mixture of the secretions of its salivary glands with comminuted fragments of wood, after the fashion of wasps. It is a moderate-sized ant, much larger than the little L. niger, and is of a black colour and remarkably shining; it gives off a very strong but by no means disagreeable odour, and may be seen on the hollow trees it frequents, stalking about in large numbers in a slow and aimless manner that contrasts strikingly with the active, bustling movements of so many of its congeners. When this species finds suitable trees near one another, a colony is established in each; the number of individuals thus associated becomes very large, and as the different colonies keep up intercommunication, this habit is very useful for purposes of defence. Forel relates that he once brought a very large number of Formica pratensis and liberated them at the base of a tree in which was a nest of L. fuliginosus; these latter, finding themselves thus assaulted and besieged, communicated in some way, information of the fact to the neighbouring colonies, and Forel soon saw large columns of the black creatures issuing from the trees near by and coming with their measured paces to the assistance of their confrères, so that the invaders were soon discomfited and destroyed. Although the European and North American representatives of the sub-family Camponotides live together in assemblies comprising as a rule a great number of individuals, and although the separate nests or formicaries which have their origin from the natural increase of a single original nest keep up by some means a connection between the members, and so form a colony of nests whose inhabitants live together on amicable terms, yet there is no definite information as to how long such association lasts, as to what is the nature of the ties that connect the members of the different nests, nor as to the means by which the colonies become dissociated. It is known that individual nests last a long time. Charles Darwin has mentioned in a letter to Forel that an old man of eighty told him he had noticed one very large nest of Formica rufa in the same place ever since he was a boy. But what period they usually endure is not known, and all these points probably vary greatly according to the species concerned. It has been well ascertained that when some ants find their nests, for some unknown reason, to be unsuitable the inhabitants leave their abodes, carrying with them their young and immature forms, and being accompanied or followed by the various parasites or commensals that are living with them. Wasmann and other entomologists have observed that the ants carry bodily some of their favourite beetle-companions, as well as members of their own species. Forel observed that after a nest of Formica pratensis had been separated into two nests placed at a considerable distance from one another so as to have no intercommunication, the members yet recognised one another as parts of the same family after the lapse of more than a month; but another observation showed that after some years of separation they were no longer so recognised.
Although it is now well ascertained that ants are able to distinguish the individuals belonging to their own nests and colonies from those that, though of their own species, are not so related to them, yet it is not known by what means the recognition is effected; there is, however, some reason to suppose that it is by something of the nature of odour. One observer has noticed that if an ant fall into water it is on emerging at first treated as if it were a stranger by its own friends; but other naturalists have found this not to be the case in other species. Contact with corrosive sublimate deprives ants for a time of this power of recognising friends, and under its influence they attack one another in the most ferocious mariner.
The nests and colonies of the species of Camponotides we have considered are all constructed by societies comprising a great number of individuals; there are, however, in the tropics numerous species that form their nests on foliage, and some of these contain only a few individuals. The leaf-nests (Fig. 64) of certain species of Polyrhachis are said to be formed of a paper-like material, and to contain each a female and about 8 or 10 worker ants. Forel[[65]] has examined nests of several Indian species, and finds they differ from those of other ants in consisting of a single cavity, lined with silk like that of a spider. These nests are further said to be constructed so as to render them either inconspicuous or like other objects on the leaves; P. argentea covers its small dwelling with little bits of vegetable matter, and a nest of P. rastella was placed between two leaves in such a manner as to be entirely hidden. All the species of the genus do not, however, share these habits, P. mayri making a card-nest, like Dolichoderus and some other ants. The species of the genus Polyrhachis are numerous in the tropics of the Old World.
Fig. 64—Nest of Polyrhachis sp. (After Smith.)
Forbes noticed that a species of this genus, that makes its paper-like nest on the underside of bamboo-leaves produces a noise by striking the leaf with its head in a series of spasmodic taps. The same observer has recorded a still more interesting fact in the case of another species of this genus—a large brown ant—found in Sumatra. The individuals were "spread over a space, perhaps a couple of yards in diameter, on the stem, leaves, and branches of a great tree which had fallen, and not within sight of each other; yet the tapping was set up at the same moment, continued exactly the same space of time, and stopped at the same instant; after the lapse of a few seconds all recommenced at the same instant. The interval was always of about the same duration, though I did not time it; each ant did not, however, beat synchronously with every other in the congeries nearest to me; there were independent tappings, so that a sort of tune was played, each congeries dotting out its own music, yet the beginnings and endings of the musical parties were strictly synchronous."
Fig. 65—Polyrhachis pandurus, worker. Singapore.