FIG. 7. Worker of Lasius niger: a. head; b. scale on petiole from behind; c. side view of tail segments to show ring of hairs around the circular orifice. The whole body is covered with a light pubescence and there are short, erect hairs on the scape of the antenna but none of these have been shown.

      CHARACTERISTICS AND DISTRIBUTION

      Only four of the nine or so sub-families of the family Formicidae are represented in this country. Two of these, Ponerinae and Dolichoderinae, have only one genus here. Of the other two the Myrmicinae have ten and the Formicinae two genera. The Ponerinae and Myrmicinae have certain similarities and are grouped together in a poneroid complex whereas the Dolichoderinae and Formicinae are included in a myrmecoid complex (named after the basic Australian sub-family Myrmeciinae).

      The Ponerinae contain a mixture of very primitive and highly-evolved forms which are mainly tropical and Australian in distribution. In southern Europe there are at present some nine species but fossil evidence shows that there were once many more. Primitive features are the possession of a sting in the females (as in wasps) and the structural similarity between queens and workers; the latter lack only wings and ocelli. All ponerines have a constriction between the first and second segments of the gaster; here the integument forms, on the underside, an organ for stridulating. They feed largely on small animals and show foraging behaviour that ranges from the highly individual to the advanced legionary type. Larvae are able to eat prey directly and even to move about the nest slightly in the less advanced genera.

      Ponera coarcta has a worldwide distribution but occurs in only 13 of the 152 vice-counties of the British Isles, all in southern England. Its colonies are small and inconspicuous and usually live in woodland amongst the stones and moss of the soil surface. There is another species, Hypoponera punctatissima, that is commonly found in glasshouses and, very rarely, in sunny situations outside.

      The Myrmicinae are thought to have evolved from ponerine ants; both groups retain stings and have a tendency to a thick, wrinkled cuticle with spines on the mesosoma. The myrmicine workers have a much simpler and smaller form than the queens. Their waist comprises two segments; this waist gives extraordinary flexibility to the gaster, and enables the sting at its tip to be brought round under the body and pushed forwards in front of the head. The integuments of the second waist on the first gastral segments form a stridulatory organ on the upper side instead of the underside, as in the ponerines. Only in the more primitive genera do the workers lay eggs. Seed-eating is common in this sub-family; it also includes the only group to have perfected a method of culturing and eating fungi. Many genera have evolved social parasitism; of the ten indigenous here half show this tendency.

      Undoubtedly the most widespread genus in the British Isles is Myrmica. It is a brownish-red ant found in many different habitats, in small colonies that rarely exceed 3000 workers. They sting effectively and painfully if disturbed. Myrmica reaches into every one of our islands. There are eight species; one, Myrmica ruginodis, is apparently the only ant to have colonized Shetland and the only species so far which has been found in all of the 152 vice-counties. At the opposite extreme there is Myrmica speciodes found only in Kent and Sussex, although it is more common in Europe. This is one genus which shows hardly any geographical bias here, for of the eight species which occur in southern England, six are also found in Scotland.

      The next most common genus is Leptothorax, although only one of its four species (Leptothorax acervorum) is widely, though patchily, distributed throughout the British Isles. It is a small, brown ant living in small colonies rich in queens, nesting in quite hard wood or in twigs or under the surface crust of soil. The other three species are restricted to southern England.

      Tetramorium caespitum is the only species of this genus (which is predominantly African) in the British Isles. It is a small, black ant spread widely over central Europe but restricted here to the south and farther north to coastal zones. Such habitats have a high incidence of sunshine in spring so that the soil surface where the ants nest is warmed early in the season. Furthermore, temperatures do not fall very much in winter, especially on the western coasts. Tetramorium caespitum makes large, highly-organized colonies in lowland heath in the south. In autumn it collects and stores the seeds of heather and grass for spring feeding.

      Two myrmicine genera are parasitic on Tetramorium caespitum in this country. One, Strongylognathus (one species Strongylognathus testaceus), has workers of about the same size and shape as its host but they are pale brown and have curved, toothless mandibles. The sexuals are not much bigger and contrast strikingly with the large black queen of Tetramorium. It is rare, even where it is known to exist in Dorset and Hampshire. The other