ANIMALS WHICH LIVE ON OR WITHIN GROUSE 189 



Till recently it had been thought that the Grouse-fly was the same 

 species as the common bird-fly, 1 but recently Mr D. Sharp has pointed 

 out that it is a distinct species. It is distinguished from the common 

 bird-fly by its " peculiar lurid blackish colour, without any trace of 

 green even on the feet or legs," and by other characters which have 

 been quoted in the more anatomical portion of the Committee's Report. 

 Recently yet another species 2 has been separated off from the common 

 bird-fly, so that we now have three species of Ornithomyia in this 

 country, and probably more will be added as the group is further 

 studied. 



We do not know the exact relations of the Grouse-fly to the Grouse. 

 It is believed to suck its blood, 3 and it certainly bites human beings. 

 For a time it seems to burrow amongst the feathers of the bird, and 

 any one handling Grouse during the summer is likely to disturb a fly or 

 two. They come buzzing out, and are apt to crawl up one's sleeve. 

 The feet, although large, are very beautiful. They are provided with 

 a pair of very large hooks (PI. xix. Fig. 1). Altogether, these insects 

 have a sinister aspect, and to people who do not like flies they are 

 very repellent. They occur freely in larders where freshly killed Grouse 

 have been placed, and after a short time they leave their dead host 

 and accumulate upon the windows. 



The earliest month in which the Grouse-fly has been found is in 

 June, towards the latter end. The latest is in October. They are 

 most plentiful in August. 



The females seem to be commoner than the males, or, it may be that 

 in August they are more readily caught. Like other horse-flies, forest- 

 flies, and sheep-ticks, the Grouse-fly does not^lay eggs, but the ovaries 

 produce one large egg at a time, and this passes into a dilated oviduct 

 which acts as a uterus, and here the egg develops. After attaining a 

 certain stage of development, the larva surrounds itself with a pupa or 

 chrysalis skin and is extruded. The chitinous or horny covering of 

 the larva hardens and blackens with exposure to the air, and forms the 

 so-called pupa-case ; in fact, one may almost say the young are hatched 

 as pupae. At no time is the larva exposed, though there is a larval 

 stage free in the uterus of the mother wrapped first in the egg-shell and 

 then in the pupa-case. 



The pupae were found during August and September. They are 

 black, shiny, seed like looking objects, and appear to be deposited 

 amongst the feathers, from which they are easily detached. The few we 

 have found either dropped on some paper over which we were handling 

 birds, or lay loose at the bottom of the cardboard boxes in which Grouse 

 travel. Probably they take some eight or nine months before they 

 give rise to the adult fly, and the latter very likely disappear altogether 

 from about October till June. Further research is needed^to^ throw 

 light on these questions. 



Three specimens of the Grouse-fly, all of them taken from one bird, 



1 Ornithomyia avicularw, Lin. 2 0. fringillina, Bezzi. 



s Proc. Zool. Soc. Lond., 1910, p. 704. 



