318 MEDICAL ENTOMOLOGY 



Antennae approximated or contiguous ; body elongated, some- 

 what broader in front than behind (Deer) . . , . Cephenomyia. 



5. No mouth booklets . . , . . . . ,- . - V- . -- '-' 6 

 Two small mouth booklets present (Rodents) .... Oestromyia. 



6. Bristly covering alike above and below (Reindeer) . . . Oedamagena. 

 Bristles stronger below than above (Ox, etc.) .... Hypoderma. 



7. Larvae oval (Rodents, Marsupials) ... . . . Cuterehra. 



Larvae club-shaped, more slender posteriorly (Artiodactyls, 



Carnivora, Primates) . . Dermatobia. 



GENUS GASTROPHILUS, LEACH 



This genus, the main characteristics of which are given in the above 

 keys, contains some fourteen species distributed all over the world. Those 

 larvae which are known live in the stomach and intestines of Equines ; 

 the adults are known popularly as ' Bot flies '. Garman gives the follow- 

 ing key for the identification of the common species : 



KEY TO THE COMMON SPECIES OF GASTROPHILUS. 



1. Discoidal cell closed by cross-vein ......... 2 



Discoidal cell open . . pecorum. 



2. Wings marked with brown ....... equi. 



Wings not marked with brown ......... 3 



3. Anterior basal cell nearly, or quite, equal to the discoidal cell 



in length nasalis. 



Anterior basal cell markedly shorter than the discoidal cell . haemorrhoidalis. 



Gustrophiliis equi, Fabr., the bot fly of the horse, is the commonest 

 species, and has long been familiar to farmers and veterinarians. The 

 fly is of a brownish colour with rows of black spots on the lower borders 

 of the abdominal segments ; the wings are pale with dark transverse bands 

 about the centre. When about to oviposit the female fly hovers near a 

 horse with its body bent downwards and the ovipositor fully extended ; 

 it then darts suddenly on to the skin and glues an egg lightly on to the 

 end of a hair, and then rapidly retreats to hover again until the next egg 

 is ready to be laid. The egg is pointed at the lower end, while the 

 upper has a well marked operculum. Osbourne, who has studied the 

 conditions under which the eggs hatch, has found that they require some 

 friction and moisture to enable them to do so, and that this is sup- 

 plied by the horse licking its skin, or that of another horse. Hatching 

 sometimes takes place before the tenth day after the eggs are laid, but 

 more usually after the fourteenth day. This knowledge is of importance 

 for it enables the horse keeper to know within what period he should 

 destroy the eggs. 



