OUTLINES OF ENTOMOLOaY. 45 



usually a conspicuous appendage of the abdomen, and is of a variety of 

 singular forms, but is not connected with any poison gland, and while 

 that of some species may intiicta sharp prick, it is in no case a true sting. 



Among the Piercers are found those species that vary most from 

 what is considered the type of the Order, many of which, in points of 

 their general structure, and in the forms of their larvce, seem to be 

 closely allied to the Lepidoptera. 



The Piercers (Terebrantia) are very conveniently separated 

 intotwo tribes : 



1. Insect eaters (Entomophaga), Parasitic flies, and also Gall- 

 flies, and a very few other vegetable feeders. 



2. Plant eaters (Phytophaga), Saw-flies and Wood-borers The 

 first tribe includes a vast number of species, some with bodies, includ- 

 ing the ovipositor, two inches or more in length, others so minute that 

 their different parts can only be distinguished with a lens, the office of 

 all of which seems to be to keep in check those members of its class 

 which prey upon vegetation, and which, but for them, would multiply 

 to such an extent as to threaten extinction to many of our most valu- 

 able food plants. 



The Parasitic species may be readily separated into three families, 

 ICHNEUMONiD^, Proctotrypid^ and Chalcidid^. Some authors 

 separate various species from these groups, for which they define sev- 

 eral more families, but those mentioned include all the more important 

 species. 



Among the members of the first-named family may be found some 

 very large species, a great number that are of medium size — with a 

 wing expanse of from one-third to one-half inch — and some that are 

 extremely small. The typical Ichneumon flies have long and rather 

 slender bodies, usually terminated by an exserted ovipositor, which is 

 composed of several thread-like stylets, and which varies in length from 

 three or four inches in Thalessa, to a scarcely noticeable point at the 

 tip of the abdomen, as in Microgastcr. 



The head is somewhat square, the antennte thread-like and many- 

 jointed ; both pairs of palpi are well developed, but the biting organs 

 are rather small and weak. The thorax is compact, but the different 

 parts are often outlined by deep grooves. The veining of the wings 

 is much like that in bees and wasps, but the membrane is more delicate 

 and transparent. The legs are smooth and cylindrical. These insects 

 lay their eggs in or upon the bodies of other insects, usually caterpillars, 

 piercing the skins with their sharply pointed ovipositors. Sometimes 

 but a single egg is laid ; in other cases the dorsal surface is thickly 



