265 



Family Conopidse — The Thick-headed flies 



Rather thinly pilose or nearly bare, elongate flics of moderate size. 



Head broad, the front broad in both sexes; ocelli present or absent. 

 Antennae with three segments, the third bearing a dorsal arista or 

 terminal style. Oral opening large, the proboscis long and slender, often 

 geniculate. Abdomen often constricted basally, the genitalia of both 

 sexes conspicuous, often large or greatly elongated in the females. 

 Anal cell closed, the first basal cell always very long, the second moder- 

 ately long; apical cell closed or much narrowed. Above the antennae 

 an inflatable ptilinum. 



The Conopids are commonly found about flowers and are sluggish 

 in flight. They occur from spring to autumn but are much more com- 

 mon during the spring and early summer. The species of Stylogaster 

 are rapid in flight, the flies being great hoverers. I have found them 

 in the tropics in rather large numbers hovering over ant armies where 

 they usually remain a few inches above the ground, suddenly disappear- 

 ing, only to reappear in another patch of sunlight. In the north I 

 have found them only about flowers of the Labiateae and have observed 

 them hovering as they sucked the nectar. Many of the species resemble 

 Hymenoptera. 



The members of this family are parasitic, mostly upon bees and 

 wasps, oviposition usually occurring during flight. There are also 

 records of parasitism on Orthoptera and the species of Stylogaster are 

 in some way connected with ants but the exact relationship is unknown. 



The generic and specific limits in the family are, for the most part, 

 not sharply drawn, and tliis is especially true in the case of Conops 

 and PhysocepJuila. There have been a number of papers published deal- 

 ing with the family in whole or in part; the most important of these 

 is referred to in the footnote.* 



KEY TO GENERA 



1. Antennae with a terminal style 2 



Antennae with a dorsal or subdorsal arista 4 



2. Face with deep lateral g'rooves 3 



Face without lateral grooves, the median carina strong; ocelli vestigial 



(4) Tropidomyia Williston 



* Van Duzee. 1927, Proc. Calif. Acad. Sci., xvi, pp. 573-604. 



