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CIRCULAR 14 8, U. S. DEPARTMENT OF AGRICULTURE 



Rocky Mountain States, but it is spreading in all directions. The 

 adult flies of this species deposit their eggs along the edge of the lips 

 and cause much annoyance to horses. The nose fly is the most dan- 

 gerous of the botflies and is the one which is responsible for many 

 accidents because its annoyance makes horses panicky and causes 

 them to run away. The bots of this species occur in the stomach and 

 duodenum, and when full grown also attach in the rectum. 



Life history. — The eggs are glued to the hair of horses by the adult 

 flies. The eggs of the common horse bot are hatched apparently by 

 the biting and licking of the horse, and are taken into the mouth on 

 the lips and tongue. The small spiny bots burrow into the mucous 

 membrane of the mouth, especially the tongue, where they remain 

 from 21 to 28 days before emerging and passing on to the stomach. 



- Figure 22. — Portion of a horse's stomach, showing bots, GastrophUus intestinalis, 

 attached to the inner lining of the stomach wall. Natural size 



The habits of the nose bot are apparently very similar to those of the 

 common bot. The eggs of the chin fly hatch without friction and the 

 young bots crawl to and enter the mouth. Whether the throat bot 

 penetrates the tongue is not yet known. When the bots reach the 

 stomach they attach themselves to its wall and remain there for a 

 period of from 8 to 12 months, during which time they attain their 

 complete larval development and then pass out of the body. While 

 the common bot and the throat bot pass out of the body directly 

 with the manure, the nose bot reattaches itself to the rectum on its 

 way out, then becomes detached and reattaches itself to the anus, 

 where it may remain for three or four days, and finally drops to the 

 ground. Usually all fully developed bots pass out of the body by 

 October and those which overwinter in the horse are the young forms. 

 These bots pupate in the ground and 20 to 70 days later emerge as 



