THE THICK-HEAD FLIES 



(Family Ccmopidce.) 



The flies of this group are rather closely related to the syr- 

 phus flies. They maybe called, after Comstock, "the thick- 

 head flies," because their heads are large and conspicuous. 

 The flies themselves are rather large, but are generally slender 

 and the abdomen is stalked, like those of some wasps. The 

 wings are usually dark and the insects themselves are dark- 

 colored, but some have yellow bands on the abdomen. Those 

 which belong to the genus Myopa are stouter and have hairy 

 legs, almost like those of a robber-fly. The big-head flies are 

 found upon flowers with the syrphus flies and their larvse are 

 parasitic, chiefly upon bumblebees and wasps, but they have 

 also been found, according to Williston, in the bodies of grass- 

 hoppers. 



The larvae of these flies live in the bodies of the full-grown 

 wasps and bees. It has been supposed that the flies enter the 

 bees' nests and place their eggs on the larvae or pupae, but the 

 adult flies always issue from the adult bees or wasps, having 

 occupied the interior of the abdomen. When full-grown they 

 frequently completely fill the abdomen. Williston has seen a 

 Conops following a bumblebee and repeatedly flying against it 

 and thinks that the eggs are deposited upon the body of the bee 

 and that after hatching the larvae bore into the abdominal cavity. 

 in one instance a big-head fly was reared from the body of a 

 bumblebee several months after the latter had been killed and 

 pinned in a collection. There is a peculiar genus in this family, 

 Stylogaster, in which the female has an ovipositor which is longer 

 than the entire body. Rather more than thirty species of thick- 

 head flies, distributed in seven genera, are known to occur in the 

 United States. 



IS4 



