54 



PARASITES OF THE DOMESTIC ANIMALS 



cut off appearance. The}' are generally deposited upon the hairs of the 

 anterior parts of the body, as upon the forelegs, breast, shoulders, and 

 under side of the body, regions which are most readily reached by the 

 lips of the horse. It is not uncommon, however, for eggs to be attached 

 to the sides of the neck, lower jaw, cheeks, mane, and other parts, the 

 larvae in such cases reaching the mouths of horses by their licking or 

 nipping at each other. 



Life History. — The eggs are deposited rapidly with their free ends 

 down, and adhere to the hairs by a viscid substance which quickly dries 



Fig. 28 — Gastrophilus intestinalis: a, egg — enlarged; b, egg — natural size; c, young larva; 

 d, young larva — much enlarged, showing spiny armature; e, oral hooks; f, body spines; g, 

 full-grown larva — twice natural size; h, adult female (after Osborn, Bui. No. 5, Bureau of 

 Entomology, U. S. Dept. of Agr.). 



and gives them a firm attachment. At this time they contain larvae 

 which have undergone a more or less advanced development. 



Observations upon the botflies during recent years have been some- 

 what disturbing to conclusions formerly held and apparently necessitate 

 a certain revision of the life histories which have generally been given for 

 them. According to the observations of Roubaud (1917) upon Gas- 

 trophilus intestinalis, the eggs of the fly do not open spontaneously, and 

 the larvae may not escape from them for several weeks. The opening 

 of the operculum and freeing of the larva probably occurs when the 

 horse rubs an itching or irritated area with his nose or bites it with his 

 teeth, the horse rarely hcldng itself. By experiments with bot larvae on 

 guinea-pigs Roubaud demonstrated that when the hatched larva is 

 brought in contact with the buccal mucosa it at once burrows into this 

 membrane and lies parallel to its surface. In two or three days it dis- 

 appears, but he notes that one was seen traveling along the side of the 



