Page:EB1911 - Volume 02.djvu/98

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87
ANT

mould and bacterial growths, and causing the appearance, on the surface of their “mushroom garden,” of numerous small white bodies formed by swollen ends of the fungus hyphae. When the fungus is grown elsewhere than in the ants’ nest it produces gonidia instead of the white masses on which the ants feed, hence it seems that these masses are indeed produced as the result of some unknown cultural process. Other genera of South American ants—Apterostigma and Cyphomyrmex—make similar fungal cultivations, but they use wood, grain or dung as the substratum instead of leaf fragments. Each kind of ant is so addicted to its own particular fungal food that it refuses disdainfully, even when hungry, the produce of an alien nest.

Guests of Ants.—Many ants feed largely and some almost entirely on the saccharine secretions of other insects, the best known of which are the Aphides (plant-lice or “green-fly”). This consideration leads us to one of the most remarkable and fascinating features of ant-communities—the presence in the nests of insects and other small arthropods, which are tended and cared for by the ants as their “guests,” rendering to the ants in return the sweet food which they desire. The relation between ants and aphids has often been compared to that between men and milch cattle. Sir J. Lubbock (Lord Avebury) states that the common British yellow ants (Lasius flavus) collect flocks of root-feeding aphids in their underground nests, protect them, build earthen shelters over them, and take the greatest care of their eggs. Other ants, such as the British black garden species (L. niger), go after the aphids that frequent the shoots of plants. Many species of aphid migrate from one plant to another at certain stages in their life-cycle when their numbers have very largely increased, and F. M. Webster has observed ants, foreseeing this emigration, to carry aphids from apple trees to grasses. It has been shown by M. Büsgen that the sweet secretion (honey-dew) of the aphids is not derived, as generally believed, from the paired cornicles on the fifth abdominal segment, but from the intestine, whence it exudes in drops and is swallowed by the ants.

Besides the aphids, other insects, such as scale insects (Coccidae), caterpillars of blue butterflies (Lycaenidae), and numerous beetles, furnish the ants with nutrient secretions. The number of species of beetles that inhabit ants’ nests is almost incredibly large, and most of these are never found elsewhere, being blind, helpless and dependent on the ants’ care for protection and food; these beetles belong for the most part to the families Pselaphidae, Paussidae and Staphylinidae. Spring-tails and bristle-tails (order Aptera) of several species also frequent ants’ nests. While some of these “guest” insects produce secretions that furnish the ants with food, some seem to be useless inmates of the nest, obtaining food from the ants and giving nothing in return. Others again play the part of thieves in the ant society; C. Janet observed a small bristle-tail (Lepismima) to lurk beneath the heads of two Lasius workers, while one passed food to the other, in order to steal the drop of nourishment and to make off with it. The same naturalist describes the association with Lasius of small mites (Antennophorus) which are carried about by the worker ants, one of which may have a mite beneath her mouth, and another on either side of her abdomen. On patting their carrier or some passing ant, the mites are supplied with food, no service being rendered by them in return for the ants’ care. Perhaps the ants derive from these seemingly useless guests the same satisfaction as we obtain by keeping pet animals. Recent advance in our knowledge of the guests and associates of ants is due principally to E. Wasmann, who has compiled a list of nearly 1500 species of insects, arachnids and crustaceans, inhabiting ants’ nests. The warmth, shelter and abundant food in the nests, due both to the fresh supplies brought in by the ants and to the large amount of waste matter that accumulates, must prove strongly attractive to the various “guests.” Some of the inmates of ants’ nests are here for the purpose of preying upon the ants or their larvae, so that we find all kinds of relations between the owners of the nests and their companions, from mutual benefit to active hostility.

Among these associations or guests other species of ants are not wanting. For example, a minute species (Solenopsis fugax) lives in a compound nest with various species of Formica, forming narrow galleries which open into the larger galleries of its host. The Solenopsis can make its way into the territory of the Formica to steal the larvae which serve it as food, but the Formica is too large to pursue the thief when it returns to its own galleries.

Slaves.—Several species of ants are found in association with another species which stands to them in the relation of slave to master. Formica sanguinea is a well-known European slave-making ant that inhabits England; its workers raid the nests of F. fusca and other species, and carry off to their own nests pupae from which workers are developed that live contentedly as slaves of their captors. F. sanguinea can live either with or without slaves, but another European ant (Polyergus rufescens) is so dependent on its slaves—various species of Formica—that its workers are themselves unable to feed the larvae. The remarkable genus Anergates has no workers, and its wingless males and females are served by communities of Tetramorium cespitum (fig. 3).


1911 Britannica-Ant-Tetramorium cespitum.png

Fig. 3.—Ant, Tetramorium cespitum (Linn.), a, Female; b, female after loss of wings; c, male;
d, worker; e, larva; g, pupa; f, head of larva more highly magnified. After Marlatt, Bull. 4 (n.s.)
Div. Ent. U. S. Dept. Agriculture.


Senses and Intelligence of Ants.—That ants possess highly developed senses and the power of communicating with one another has long been known to students of their habits; the researches of P. Huber and Sir J. Lubbock (Lord Avebury) on these subjects are familiar to all naturalists. The insects are guided by light, being very sensitive to ultra-violet rays, and also by scent and hearing. Recent experiments by A. M. Fielde show that an ant follows her own old track by a scent exercised by the tenth segment of the feeler, recognizes other inmates of her nest by a sense of smell resident in the eleventh segment, is guided to the eggs, maggots and pupae, which she has to tend, by sensation through the eighth and ninth segments, and appreciates the general smell of the nest itself by means of organs in the twelfth segment. Lubbock’s experiments of inducing ants to seek objects that had been removed show that they are guided by scent rather than by sight, and that any disturbance of their surroundings often causes great uncertainty in their actions. Ants invite one another to work, or ask for food from