PARASITES AND PARASITIC DISEASES OF HORSES 33 



the other two species and is mostly confined to the North Central 

 States and certain of the 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 dangerous 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. 

 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 3 or 4 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 winged 

 flies, ready to mate and to begin the process of egg laying once more. 



Symptoms and lesions. — Bots often occur in large numbers, and it 

 is not unusual to find several hundred of these maggots attached to 

 the stomach wall of a horse. These parasites have large mouth hooks 

 by means of which they attach themselves to the lining of the stomach 

 and upper intestine. They also bear spines on much of their body 

 surface. With this armature they are capable of irritating the lining 

 of the digestive tract with which they are in contact and of producing 

 considerable irritation and injury. The attachment of nose bots to the 

 rectum and edge of the anus before they pass out is very annoying 

 and horses have been known to dislocate bones in the tail in their 

 attempts to obtain relief from this annoyance. 



The damage caused by the adult flies, especially the nose fly, is very 

 great. Runaways may lead to serious accidents and farming is often 

 interrupted by the inability to work the frightened horses. 



Treatment. — Carbon disulfide is the most effective treatment for 

 the removal of bots. Carbon tetrachloride may also be used but is 

 much less effective. These drugs should be used in accordance with 

 the recommendations given under the treatment for large intestinal 

 roundworms. 



Tetrachlor ethylene frequently will remove from 50 to 75 percent 

 of the bots when the drug is used in single doses of 1 to 2.3 fluid ounces 

 (30 to 70 cubic centimeters) for a 1,000-pound animal after fasting 

 the horse 18 hours. The drug should not be accompanied by a purg- 



