INSECT ENEMIES OF LIVE STOCK 175 



animal. These flies closely resemble the house fly in 

 appearance, but they are outdoor insects, and not " domestic " 

 to the same extent as the house fly. Wherever horses and 

 cattle occur, there the stable fly, for that is the popular 

 name of Stomoxys calcitrans, may be found in plenty. 



In general colour the stable fly is brownish, shot with 

 green ; the upper side of the thorax is marked with four 

 longitudinal dark stripes, or, looked at in another way, 

 there are three longitudinal light stripes ; the central one, 

 which runs down the middle of the thorax, is of a character- 

 istic golden shade at its anterior or forward end. The 

 abdomen is conspicuously spotted with brown. Instead of 

 the sucking proboscis, so well known in the house fly, this 

 insect is armed with an awl-like organ, adapted for piercing 

 and sucking ; often this organ projects forward horizon- 

 tally and is then plainly seen on looking down upon the 

 insect from above. Usually the female fly lays from fifty 

 to seventy white eggs in decaying vegetable refuse, and 

 from them emerge legless larvae, very similar to those of 

 the house fly, but more shiny and translucent, and differing, 

 also, in the structure of the posterior spiracles. In a fort- 

 night to three weeks the larvae are full grown and pass to 

 the pupal stage, which lasts from a little over a week to a 

 fortnight, so that the whole life-cycle may be completed in 

 from twenty-five to thirty-seven days. 



The means of transmission is a subject of disagreement 

 among the various authorities on the disease, but the 

 identity of the reservoir for the virus is a point upon which 

 there is unanimous agreement. It will be remembered 

 that the big game of South Africa have been shown to act 

 as reservoirs for the blood parasites causing sleeping sick- 

 ness; in a precisely similar way, the capybara, Hydro- 

 chosrus capybara, a large South American rodent, acts as 

 a natural reservoir for Trypanosoma equinum. These 

 animals are common in the streams of the Chaco district 

 of Argentina and Paraguay; at times they are overcome 



