416 



NORTH AMERICAN DIPTERA 



by the curvature of the fourth longitudinal vein, this vein rarely straight 

 or almost so, sometimes obsolete apically; posterior erossvein rarely 

 absent; first, third and fifth veins sometimes bristled; basal and anal 

 cells complete. Squamae almost invariably large. Abdomen variable in 

 shape, usually bearing conspicuous bristles on the sides, apex and disc, 

 but these variable; genitalia variable in both sexes. 



The Tachinids are, insofar as known, all parasitic on other insects, 

 particularly Lepidopterous, Tenthrcdinid, and beetle larvae and adult 

 beetles, as well as Hemiptera, Orthoptera and possibly some other 

 orders of insects. One or two species are known to be parasitic on other 



Paradejeania species. 



flies (Syrphidffi). The species parasitic on Hemiptera usually have a 

 bristleless, or near bristlelcss abdomen while many of those parasitizing 

 beetles have a long, piercing ovipositor, but this character is not limited 

 to such species. The eggs are variable, some being very small (micro- 

 type), while others are large (macrotype). A small number of species 

 deposit living larvie or eggs just ready to hatch. The study of the im- 

 mature stages of the Tachinids should prove to be a most fascinating 

 one as is indicated by such work as has already been done. The species 

 of Gonia, which lay microtype eggs, scatter hundreds of them (as many 

 as a thousand) over vegetation and the ground; they are eaten by 

 feeding caterpillars and ultimately destroy their host. This may seem 

 a haphazard way of doing things but the flies are efficient parasites as 



