570 SCIENCE PROGRESS 



fly belongs live upon birds ; it particularly frequents swallows 

 and other allied species. Recently Dr. Sharp has pointed out 

 that the grouse-fly {Onithomyia lagopodis) is distinct from the 

 ordinary bird-fly {O. avicularia). The habits of the grouse-fly 

 are difficult to investigate. It is believed to suck the blood of 

 the grouse, and very probably inoculates the bird with some 

 of the protozoa which infests its blood. The adult or imago 

 burrows amongst the feathers of the bird, and any one handling 

 grouse during the late summer is apt to disturb a fly or two. 

 Their feet, although large, are very beautiful. Each is provided 

 with a pair of most powerful hooks. Altogether, these insects 

 have a sinister aspect and they are very repellent to people 

 who do not like flies. The grouse-fly occurs very frequently 

 in larders where freshly killed grouse have been placed and 

 after a short time they readily leave their dead hosts and 

 accumulate on the windows. Like the fatal tsetse-fly of 

 Africa, which conveys sleeping-sickness, they lay no eggs 

 but produce one larva or maggot at a time and this imme- 

 diately turns into a pupa. The pupae of the grouse-fly, usually 

 found in the nest of the grouse during August and September, 

 are black, shiny, seed-like-looking objects. Probably each 

 pupa takes some three-quarters of a year to develop into the 

 adult fly and the latter disappears from October until June. 

 There is thus a certain tragedy in the life of these insects. 

 No parent ever sees its offspring, no offspring has ever known 

 parental care. We have never found one of these flies in the 

 crop of the grouse, nor have we succeeded in finding cysts 

 in the bodies of flies which were broken up, or teased up, 

 or cut into sections. 



Finally there is another fly whose larva lives in grouse 

 droppings. All these creatures have been carefully searched 

 for the larva of the grouse tape-worms but so far with no 

 definite success. 



Of the fifteen endoparasites but two or three demand 

 attention ; the others are comparatively rare or innocuous, and 

 some, such as the gape— or forked — worm so fatal to pheasants, 

 are not normally parasites of the grouse. Occasionally by 

 some accident they get into the wrong Paradise. 



Some of these endoparasites, which live inside the body 

 of the grouse, are responsible for the illnesses from which 

 grouse suffer. Any attempt to control their number and their 



