130 NORTH AMERICAN DirTERA. 



53. (ESTEID^. 



Flies of moderate to rather large size, thick-set, usually 

 more or less pilose. Head large, the lower part more or less 

 swollen, Antennee short, three-jointed, decumbent, and more 

 or less sunken in the facial groove or grooves ; arista bare or 

 plumose. Mouth opening small, the mouth-parts sometimes 

 rudimentary, never large. Front broad in both sexes, in the 

 male broader in front. Eyes comparatively small, bare. 

 Ocelli present. Thorax robust, with a distinct transverse 

 suture. Abdomen short, conical or but little elongated ; gen- 

 italia of the male hidden, the ovipositor sometimes elongated. 

 Legs moderately long, the hind pair sometimes elongated. 

 Tegulae usually large ; sometimes small. Kexiration of the 

 wings Muscid-like, in most cases the first posterior cell nar- 

 rowed or closed; anal cell small, usually indistinct; discal 

 cell sometimes absent. 



This family, though of small size comparatively, is of the 

 greatest interest by reason of the habits of the larvae, all of 

 which that are known are parasitic uiiou mammals. The adult 

 flies often have rudimentary mouth-parts, and devote the 

 whole of their brief existence to the labors of procreation. 

 Only about seventy species are known, and they are generally 

 called bot-flies, though the name is frequently applied es- 

 pecially to the bot-fly of the horse. Parasitism occurs in three 

 principal ways, in the stomach and digestive tubes, in tumors 

 formed by the larvae under the skin, and in the pharyngeal and 

 nasal cavities. With but few exceptions each species is con 

 fined to a single species of mammal, and each geiuis or each 

 group of allied species is parasitic in the same way upon sim- 

 ilar animals. Seven species of Gastrojihilus are found in the 

 stomach and intestines of the horse and ass. Thirteen species 

 of Hypoderma are known to live under the skin of the horse, 

 the ox, the buffalo, the sheep, the goat, four species of an- 

 telope, and the musk deer. Two species of (Estromyia like- 

 wise infest the skin of Ldijniniix and Hj/pnrhrvs. (EdanKu/nKi 



