Next to these insects come the Gall-flies, most of which produce round galls on oaks; and in some species we meet with a wingless brood, living alternately with the winged broods, but at the roots of the trees instead of in the open air. The veining of the wings is reduced to one or two veins; the antennæ are rather long, and not angulated; and the abdomen is short, and constricted at the base. The flies seldom measure more than half an inch across the wings. Some galls are hard, like the one found on the Turkey oak, from which ink is made; while others are large and juicy, resembling cherries, or small apples, among which is the so-called apple of Sodom. Others, like the Bedeguar, which is found on roses, have a mossy appearance. The latter are produced by a small black saw-fly, with part of the legs, and, in the female, the base of the abdomen, red beneath.
Photo by W. P. Dando, F.Z.S.] [Regent's Park.
PINE-BORING WASP (FEMALE).
Formidable in appearance, but quite harmless.
Some of the smaller gall-flies do not produce galls, but are parasitic on other insects; but galls are very liable to the parasitic attacks of other insects, especially to those of small brilliant metallic green four-winged flies, belonging to an allied family, with very few nervures, but with a black membranous spot on the front edge of the fore wings, and angulated antennæ. Many galls do not begin to grow until the larva is hatched and begins to eat.
We now come to five or six families of parasitic species, popularly called Ichneumon-flies, and immensely numerous and varied. There are probably considerably over 2,000 species in England alone; but they are comparatively little known or studied. Some of these have beautifully delicate wings, fringed with long bristles, and are among the smallest insects known, being of quite microscopic dimensions. These are parasitic on the eggs of various insects, and some are aquatic. But the more typical ichneumon-flies are of larger size, often measuring more than an inch across the wings. Their bodies are usually black or yellow, and there is often an irregularly shaped space in the middle of the fore wing, where the veins of the wing converge. In these flies the ovipositor is very short; but in others it is of great length, especially in the case of the largest British insect of this group, which is parasitic on the larvæ of the great black-and-yellow wood-wasp, of which we have already spoken. This parasite is as large as the wood-wasp, but much more slender; it is black, with red legs, and two white dots on each segment of the abdomen. The ovipositor, which looks like three black threads, is as long as the whole body.
Photo by W. P. Dando, F.Z.S., Regent's Park.
PINE-BORING WASP (MALE).