GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 49 



very active, and as they deposit only one egg at a time they are not 

 so frequently seen about horses as are the adults of the common bot- 

 fly. They take no food in the adult stage. Their length of life is 

 from 1 to 7 days. 



The throat bot-fly (G. nasalis) deposits its eggs on the hairs under 

 the jaws and to some extent on the shoulders and other parts of the 

 host. The larvae of this species attach themselves to the walls of the 

 pharynx and also to those of the stomach and duodenum. They do 

 not reattach in the rectum or at the anus as do the bots of the nose 

 fly. Pupation occurs in from 1J to 2 days after the larvae have 

 passed from the host, and adults emerge in from 20 to 56 days later. 

 The adults are somewhat longer lived than those of the nose fly. 

 The flies cause considerable annoyance to horses during oviposition 

 but not as serious as in the case of the nose fly. 



The common bot-fly (G. intestinalis) usually appears later in the 

 season than the nose fly and becomes most abundant just before kill- 

 ing frosts. The eggs are deposited on all parts of the body, but 

 preferably on the fore legs. They hatch upon the application of 

 moisture and friction. From 9 to 11 days after oviposition appears 

 to be the most favorable period for hatching, although some may 

 hatch as early as 7 days and others as late as 96 days after oviposi- 

 tion. The larvae attach in any part of the stomach, but the last-stage 

 bots are found mostly in the left sac. They continue to drop from 

 the host for a long period of time. Pupation takes place in protected 

 places on the surface of the soil and the pupa stage lasts from 40 to 

 60 days. 



All Gastrophilus larvae are surprisingly resistant to chemicals. 

 The treatment of horses with carbon disulphid in three doses followed 

 by a physic is satisfactory if administered in the late fall. Spring 

 treatment is less effective, as the full-grown larvae are more resistant, 

 and many of the nose-fly bots have left the stomach and passed back 

 to the rectum at that time. 



Larvae of G. haemorrhoidalis may be removed from the rectum 

 mechanically, but this is laborious. The use of enemas containing 

 insecticides is ineffective. 



As a repellent, pine tar mixed with other material gave good re- 

 sults against the common bot-fly and the throat bot-fly. Such mix- 

 tures may be utilized to cause the flies to lay eggs on parts of the body 

 less accessible to the horse's mouth. 



Various nose protectors are in use against G. haemorrhoidalis, but 

 there are objections to many of them. A piece of leather suspended 

 below the lips from the bit rings is simplest and best. For animals 

 on pasture a halter with a box-like arrangement and throat cover has 

 been devised to protect horses against infestation by all three species. 



