The Diseases and Parasites of Wild Ruffed Grouse 227 



and develop into infective larvae in the body cavity. The sowbugs 

 are then eaten by grouse (or other primary host species). In the 

 bird's digestive tract, the larvae mature and attach themselves to 

 the proventricular wall. When mature, they lay eggs free in the 

 digestive tract to be carried out in the droppings, thus completing 

 the round. 



The occurrence of Dispharynx is quite local, and varies greatly 

 in different years. So far as is now known, it has been a serious grouse 

 parasite only in the area from New York and New Jersey through 

 southern New England. Of four hundred and forty-three birds ex- 

 amined by Allen and Gross ( 1926 ) from five states, several of which 

 had been picked up dead, forty-nine (eleven per cent) had Dis- 

 pharynx infestations. None of these stomach worms were found in 

 four hundred and four birds from ten other states and provinces. 

 Of 2,059 adult wild grouse examined during the New York study 

 (N. Y. S. Cons. Dept. Ann. Reports 1932-42) about three hundred 

 and fifty contained Dispharynx, an average infection of seventeen 

 per cent. The rate of infection varied from sLx and five-tenths per 

 cent in 1933 and seven and seven-tenths per cent in 1932 ( and prob- 

 ably less in 1931 and 1930 ) to twenty-eight and two-tenths per cent 

 in 1942. The rate increased generally from 1932 to 1938 when it 

 reached twenty per cent. Then it declined to six and five-tenths per 

 cent in 1939, whence it again increased each year until 1942. Serious 

 cases were not uncommon, as in 1934 when eight out of eighteen 

 cases "were thought serious enough to have caused death in due 

 time." 



The parasite occurs in young grouse too. The New York State 

 Conservation Department Annual Reports from 1933 to 1941 (ex- 

 cept 1936 ) summarize the examinations of nine hundred and thirty- 

 two chicks, of which fifty-four or five and eight-tenths per cent had 

 Dispharynx. The annual rates of infection varied from zero (1933 

 and 1934) to ten and two-tenths per cent in 1940. 



Since these birds were collected from various parts of the state 

 and at all seasons ( chicks only in summer, of course ) , the probability 

 of obtaining a true estimate of the rate of infection from the number 

 of cases is slight. However, there is some indication, particularly as 

 indicated from the records of the adults, that the incidence of this 

 parasitism fluctuates more or less periodically, building up to a large 

 number of cases, then falling off, and so on. Further, the high in- 



