3o6 THE LIVING ANIMALS OF THE WORLD 



Fhili t, n . f. iljnjj, F.Z.i.] [Kegtnl'i Part 



PINE-BORING WASP (FEMALE) 



Formldablt in /Jppew afue^ but ffuite harmUa 



short, and constricted at the base. The flies seldom measure more than half an inch across the 

 wincrs. 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 Ikdeguar, 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. 



Some of the smaller .gall-flies do not pro- 

 duce 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, belong- 

 ing to an allied family, with very few nervures, 

 but with a black membranous spot on the 

 front edge of the fore wings, and angulated 

 antcnn.T. 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 IcHXEi'MON- 

 FI.IES, and immensely numerous and varied. 

 There are probably considerably over 2,000 

 species in England alone ; but they are com- 

 paratively 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 arc 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, especiall}' in the case 

 of the largest British insect of this group, which is 

 parasitic on the larvae of the great black-and-}-cllow 

 wood-wasp, of which we have alread)' 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. 



The numerous parasites of which we have spoken 

 usually deposit their eggs in punctures in the bodies 

 of caterpillars or other immature insects, which the grubs 

 devour from within during the life of their victim, 

 leaving it to die when they themselves have reached 

 their full growth. 



Intermediate between the boring and stinging insects 

 of this order comes the small family of the RUBV-TAILED 

 Flies. These are brilliantly coloured bronze-red, blue, 



or green metallic four-winged flies, with the thora.x covered with large depressions, and the 

 abdomen smooth, and usually composed, as seen from above, of one large, smooth joint, and 

 one or two much smaller coarsely punctured ones beyond it, the last ending in a variable 

 number of short teeth. They roll themselves up in a ball when alarmed, and are parasites, 

 depositing their eggs in the nests of other insects. An entomologist once saw a ruby-tailed 



Fhm by (f. p. Dan Jo, F.Z.S. 



PINE-BORING W.A.SP (MALE) 



Stnallf- than the female^ andi'ery dijfcietu in appearance 



