148 NORTH AMERICAN DIPTERA 



Family Tabanidae — The Horse Flies 



Chrysops species. 



Bristleless flies of medium to large size, the eyes usually bi-colored 

 in life. 



Head large, the occiput flattened or concave. Eyes large, short 

 pilose or bare, usually holoptic in the males and often with some of the 

 facets much larger than the others; ocelli present or absent. Proboscis 

 projecting, sometimes longer than the body; palpi with two segments, 

 the second segment variable in different genera and sometimes in the two 

 sexes. Antennae porrect, composed of three segments, the third com- 

 posed of three to eight annuli. Thorax and abdomen clothed with fine 

 hairs. Abdomen broad, composed of seven visible segments; genitalia 

 never prominent. Legs moderately stout, the tibiee sometimes much 

 dilated; middle tibiffi always with two spurs at the tips; empodium 

 developed pulvilliform, the pulvilli alwaj's present. Wings with two 

 submarginal and five posterior cells; basal cells large; anal cell usually 

 closed near the wing margin; costa extending around the entire wing. 

 Squamffi large. . 



The Tabanids are common in all parts of the world. They have 

 been given various common names, such as Horse Flies, Deer Flies, 

 Greenheads, Bullheads, etc. The adults of most species are serious pests 

 of mammals and man is not excepted. One type of filariasis is trans- 

 mitted by the adults and both the fly and host are essential in the life 

 cycle of the parasite causing the disease. One of the best ways of 

 collecting these insects is to capture those causing irritation during 

 collecting trips. Since the larvae of many species are aquatic the adults 

 may usually be found near water and in the case of some species the 

 males are rare except adjacent to the breeding places, and, as this sex 

 does not suck blood they must be looked for in places other than in 

 the vicinity of warm blooded animals, the same being true for most of 

 the genera of the Pangoniinse, although the genus Chrysops of this 



