272 MEDICAL ENTOMOLOGY 



eyes are separated by a broad white band, at the lowest border of which 

 there are certain small dark longitudinal or transverse callosities or calli. 

 Ocelli may be present or absent. Proboscis short or projecting down- 

 wards, or long and projecting forwards. Palpi two-jointed, stout, of a 

 pale creamy colour, as long as the proboscis or much shorter. Thorax 

 broad, covered with fine hairs, never with bristles, and with or without 

 stripes or other markings. Abdomen broad, composed of seven visible 

 segments, and covered with delicate hairs, never with bristles ; it may be 

 marked with spots and bands. Male genitalia never prominent. Legs 

 stout, tibiae sometimes dilated, middle tibia with two spurs at the tip. 

 Empodium well developed, pulvilli always present. Venation character- 

 istic and without much variation; two submarginal and five posterior 

 cells present. The costal vein encircles the entire wing; the anterior 

 branch of the third longitudinal vein often has a short backwardly 

 directed spur. Wings often dark, with interrupted bands, clear flecks or 

 rings. Squamae of large size. Reproduction oviparous, eggs laid in a 

 mass on leaves or twigs over or near water. Larvae whitish, cylindrical 

 in shape and tapering at both ends ; they may be ringed or striped, and 

 are provided with pseudopods and rows of small spines for locomotion. 

 The pupa resembles that of Lepidoptera, but has large ear-shaped spir- 

 acles on the dorsum of the thorax. 



This family is an extremely large one, no less than 2,500 species hav- 

 ing been recorded up to the present time. It is widely distributed, 

 and many of the species are common in favourable localities. The 

 males throughout the family, and the females in many of the genera, 

 are flower feeders or live upon vegetable juices. In some of the genera, 

 such as Tabanus, Haematopota and Chrysops the females are blood- 

 suckers, and the commoner species, which are brought to notice by their 

 habits, have received various local names, such as ' gad flies ', ' horse 

 flies ', ' clegs ', ' seroot flies '. They feed mainly upon cattle and horses, 

 but will occasionally attack man. The males of many of the species 

 are very rarely met with, even in localities in which the females are 

 quite common. 



Several observers have attempted to incriminate flies of this family as 

 transmitting agents in certain trypanosome diseases of equines and 

 camels, such as Surra and Debab, in India and North Africa. The 

 evidence in the majority of instances is circumstantial, and is not 

 borne out by transmission experiments. It is possible that the Taba- 

 nidae may transmit the trypanosomes accidentally. (See Chapter XII.) 



