M. V. Brian - Ants

Only one more moult is needed before the adult is produced. This forms with much less change in shape inside the pupal skin. The wings flatten, elongate and fold up and the legs and antennae and petiole segments narrow a little more. Colour appears as a gradually increasing brownness in the general body but the eyes change from pink to black. The adult emerges with a very soft flexible skin and the wings, if any, inflate, spread out and set hard.

The caste differences in the female do not develop until very near the end of larval life. In workers the wing buds stop growing when they are quite small and all traces vanish by the time the pupa is formed; their ovary never thickens and splits into egg tubes but simply elongates to meet the oviduct. Caste differences in ants thus depend quite simply on whether buds grow or not; there is no degeneration and reorganization as happens in the honeybee. It seems likely that the growth of wings and ovaries is specially delayed during the development of females so that caste determination can be left to the last moment.

In males, which have only one caste, the wing grows earlier and the testis is split longitudinally very early in the larval stage. Late caste determination presumably gives a more sensitive response to social conditions.

Males are either the same size or smaller than the females and they are usually darker. Their antennae are straighter and clumsier and cannot be folded back against the head. They have well-developed compound eyes and ocelli. Their thorax, like that of the sexual females, carries two pairs of wings linked by hooks and it is composed of plates separated by sutures but their petiole is not quite so well-developed. There is no sting at the end of the abdomen; in its place are appendages for locking on to the female during copulation. They do not possess large body reserves like the sexual females.

Three keys are given here: the first to sub-families, the second to genera and the third to species. These are based on characteristics shown by workers and, in those species which lack them, queens; males help a great deal but for simplicity have been left out. To identify ants as far as the species is difficult; indeed, experts are often not in agreement about some very similar forms. Nevertheless the four main genera, Myrmica , Leptothorax , Lasius and Formica , have been here divided into their most common and easily identified species. The key is not based solely on structural features but includes in a few places reference to habitat, nest site and shape and other aspects of natural history. A low-powered stereoscopic microscope is best for assessing many characteristics but a hand lens may sometimes be adequate. Many distinctions are comparative, e.g., hairy or not hairy, and it is obvious that in these cases experience and reference to a reliable, modern collection is essential.

Key to sub-families

Key to genera

Key to species

FIG. 6. Worker of Myrmica rubra : a. head, b. foreleg, c. scape of antenna, d. Myrmica scabrinodis: scape of antenna. c. and d. are viewed from behind. Hairs are abundant on the head which is strongly corrugated.