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demand for army horses, has developed a serious fly nuisance, by 

 providing ideal breeding conditions for this bot-fly. Other species 

 implicated are G. intestinalis {equi) and G. nasalis. A key to these 

 is given, based on wing venation, as well as one to the larvae of this 

 genus. 



All these species occur in the United States, G. intestinalis and 

 G. nasalis being widely distributed, while G. haeniorrJioidalis is confined 

 to the north-central and northern Rocky Mountain States. They are 

 all a source of considerable injury to horses, owing to the worry caused 

 by the flies at the time the eggs are laid, and by the attachment of 

 the larvae in the alimentary tract. 



G. haemorrhoidalis (nose-fly) is by far the most amioying to horses 

 at the time the eggs are laid, the effects of oviposition on pastured 

 animals being loss of flesh and mechanical injuries due to subsequent 

 rubbing against posts and barbed wire. In the case of unprotected 

 work animals the results are often complete loss of self-control, leading 

 to accidents, which are especially serious when the horses are being 

 used for mowing. The eggs are deposited singly in the pores of the 

 minute hairs on the lips, and those near the edges which are kept 

 moist and receive friction hatch in from 5 to 10 days. The larvae 

 are ingested with food or water and attach themselves to the walls 

 of the stomach, where they remain till the following winter or spring 

 and then migrate to the rectum, where they re-attach themselves. 

 Before leaving the host they usually attach close to the anus, and 

 protrude from it, becoming accustomed to the air temperatures and 

 assuming a greenish colour. At this time their mobility increases. 

 After remaining in this position for from 40 to 71 hours they drop, 

 but not with the manure, as is supposed, for when this is dropped 

 during their attachment they seem to use more effort in clinging 

 and are only pushed aside during its passage. After dropping to the 

 ground the bots penetrate into the soil to a slight depth for protection 

 and pupate 18 to 170 hours later. After a pupal stage of 21 to 68 

 days the adults appear, early in June, reaching the maximum of 

 abundance during the first half of the season and disappearing with 

 the frosts. The length of fife is only 1-7 days, during which time 

 they take no food, but are very active, the females ovipositing through- 

 out their existence, the average number of eggs being about 150. 



G. nasalis, L. {veterinus, Clark ; salutifenis, Clark ; clarkii, Leach ; 

 duodenalis, Schwab) (throat bot-fly) deposits its eggs on the hairs 

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

 of the host. The larvae attach themselves to the walls of the pharynx, 

 in which position they cause paralysis of the muscles of deglutition, 

 resulting in inability to take food and drink and in extreme cases 

 in death. They also attach themselves to the walls of the stomach 

 and duodenum, but do not re-attach in the rectum or at the anus. 

 Pupation occurs in 1|- to 2 days after the larvae have passed from 

 the host in its droppings, and adults emerge 20-56 days later. The 

 adults are rather longer lived than those of G. haemorrhoidalis, and 

 though they cause considerable annoyance to horses during oviposition, 

 it is not so great as is the case with that species. 



G. intestinalis, De G. {bovis, L. ; equi, Clark ; gastricus major, 

 Schwab) (common bot-fly) usually «kppears later in the season than 

 G. haemorrhoidalis and becomes most abundant just before frosts 



