GENUS HYPODERMA 319 



Gastrophilns haemorrhoidalis, L., the red-tailed hot fly, is another 

 species the larvae of which are parasitic in the stomach of the horse. 

 It is a small fly and can be recognized by the orange red tip of the 

 abdomen ; it oviposits on the nose and lips of the horse. Its eggs are of 

 a dark colour, and at the time they are laid contain nearly developed 

 embryos, so that they hatch out much more quickiy than those of equi. 



Gastrophilus nasalis, L., the ' Chin fly ' has much the same habits 

 as the former species, depositing its eggs on the lips and margins of the 

 nostrils of the horse. 



GENUS OESTRUS, L. 



This genus contains the well known Oestrus ovis, L., the bot fly 

 or head maggot of the sheep, known to man from ancient times. It 

 deposits its larvae in the nostrils of sheep, from which they migrate into 

 the frontal sinuses, causing much discomfort to the animal ; when in 

 large numbers they have been known to cause the death of the host. The 

 larvae attach themselves by their hooks to the membraneous lining 

 of the cavities and feed on the secretion which surrounds them ; 

 when about to pupate they either crawl out of the nasal chambers 

 or may be sneezed out. The pupal stage lasts about two months. 

 The fly is found almost throughout the world. 



GENUS HYPODERMA, LATRIELLE 



The oestrids belonging to this genus are commonly known in 

 America as ' Warble flies ', or ' Heel flies '; they are characterized by the 

 complete absence of palpi ; their larvae are parasites of the hides of 

 cattle, and as such cause great loss to farmers. In a recent paper on 

 Warble flies from Canada, Hadwen points out that the average percent- 

 age of infected hides (' grubby hides ') in the provinces of New 

 Brunswick, Quebec, Ontario, and British Columbia amounts to 

 32'22 per cent. This loss falls mainly on the farmer, for warbled hides 

 are of little or no value. 



The warble season in Canada, from the tanner's point of view, extends 

 from late January to early July, the worst period being during the month 

 of April. Hadwen found that the first larvae of Hypoderma bovis, 

 de Geer, emerged from the skins on April 10th, and the last about 

 Jul}* 2nd. The larvae were most prominent in the hides about April 

 10th, and had perforated the skin some time before. Hadwen states that 

 all tanners are agreed that rough, long-haired, ill-kept animals are those 

 which are chiefly attacked ; well-kept, sleek anirnals are rarely parasitised. 



