Mr. Peal has also recorded that an ant—the name is not mentioned, but it may be presumed to be an Assamese species—makes a concerted noise loud enough to be heard by a human being at twenty or thirty feet distance, the sound being produced by each ant scraping the horny apex of the abdomen three times in rapid succession on the dry, crisp leaves of which the nest is usually composed. These records suggest that these foliage-ants keep up a connection between the members of different nests somewhat after the same fashion as do so many of the terrestrial Camponotides. Although the species of Camponotides have no special organ for the production of sound in the position in which one is found in Myrmicides and Ponerides, yet it is probable that they are able to produce a sound by rubbing together other parts of the abdomen.
Sub-Fam. 2. Dolichoderides.—Hind body furnished with but one constriction so that only a single scale or node is formed; Sting rudimentary; the poison-sac without cushion.
Fig. 66—Tapinoma erraticum, worker. Britain. Upper side and profile.
The Dolichoderides are similar to Camponotides in appearance, and are distinguished chiefly by the structure of the sting and the poison apparatus. To this we may add that Forel also considers the gizzard to be different in the two sub-families, there being no visible calyx in the Dolichoderides, while this part is largely developed in the Camponotides. This is one of the least extensive of the sub-families of ants, not more than 150 species being yet discovered. Comparatively little is known of the natural history of its members, only a very small number of species of Dolichoderides being found in Europe. The best known of these (and the only British Dolichoderid) is Tapinoma erraticum, a little ant of about the size of Lasius niger, and somewhat similar in appearance, but very different in its habits. T. erraticum does not cultivate or appreciate Aphides, but is chiefly carnivorous in its tastes. Our knowledge of it is due to Forel, who has noticed that it is very fond of attending the fights between other ants. Here it plays the part of an interested spectator, and watching its opportunity drags off the dead body of one of the combatants in order to use it as food. Although destitute of all power of stinging, this Insect has a very useful means of defence in the anal glands with which it is provided; these secrete a fluid having a strong characteristic odour, and possessing apparently very noxious qualities when applied to other ants. The Tapinoma has no power of ejecting the fluid to a distance, but is very skilful in placing this odorous matter on the body of an opponent by touching the latter with the tip of the abdomen; on this being done its adversary is usually discomfited. This Insect is subterranean in its habits, and is said to change its abode very frequently. T. erraticum occurs somewhat rarely in Britain. Forel has also noted the habits of Liometopum microcephalum, another small European species of Dolichoderides. It is a tree-ant, and by preference adopts, and adapts for its use, the burrows made by wood-boring beetles. It forms extremely populous colonies which may extend over several large trees, the inhabitants keeping up intercommunication by means of numerous workers. No less than twelve mighty oaks were found to be thus united into a colony of this ant in one of the Bulgarian forests. The species is very warlike, and compensates for the extreme minuteness of its individuals by the skilful and rapid rushes made by combined numbers on their ant-foes of larger size.
Fritz Müller has given a brief account, under the name of the Imbauba ant, of a Brazilian arboreal ant, that forms small nests in the interior of plants. The species referred to is no doubt an Azteca, and either A. instabilis, or A. mulleri. The nests are founded by fertilised females which may frequently be found in the cells on young Cecropia plants. Each internode, he says, has on the outside, near its upper part, a small pit where the wall is much thinner, and in this the female makes a hole by which she enters. Soon afterwards the hole is completely closed by a luxuriant excrescence from its margins, and it remains thus closed until about a dozen workers have developed from the eggs of the female, when the hole is opened anew from within by the workers. It is said that many of the larvae of these ants are devoured by the grubs of a parasite of the family Chalcididae. This Insect is thought to protect the plant from the attacks of leaf-cutting ants of the genus Atta.
We may here briefly remark that much has been written about the benefits conferred on plants by the protection given to them in various ways by ants: but there is reason to suppose that a critical view of the subject will not support the idea of the association being of supreme importance to the trees.[[66]]
Sub-Fam. 3. Myrmicides.—Pedicel of abdomen formed of two well-marked nodes (knot-like segments). Sting present (absent in the Cryptocerini and Attini). (It should be noted that the workers of the genera Eciton and Aenictus of the subfamily Dorylides have, like the Myrmicides, two nodes in the pedicel.)
This sub-family consists of about 1000 species, and includes a great variety of forms, but, as they are most of them of small size, they are less known than the Camponotides, and much less attention has been paid to their habits and intelligence. Forel, until recently, adopted four groups: Myrmicini, Attini, Pseudomyrmini and Cryptocerini; but he is now disposed to increase this number to eight.[[67]] They are distinguished by differences in the clypeus, and in the form of the head; but it must be noted that the characters by which the groups are defined are not in all cases fully applicable to the males. The Cryptocerini are in external structure the most highly modified of Hymenoptera, if not of all the tribes of Insecta.
