The objectives were (1) to survey the helminthfauna of the beaver, Castor canadensis, collected in western Maryland, particularly Garrett County, (2) to relate the helminth infections to sex, age, weight, and general condition of the beaver, and (3) to record any evidence of gross pathology involving helminths.

A sample of 63 beaver, 31 males and 32 females, was obtained from Garrett, Alleghany, and Washington Counties in Maryland through fur sealing stations and the University of Maryland Natural Resources Institute at LaVale. Five helminths were found. Travassosius americanus infected 98,4%; Castorstrongylus castoris, 96.8%; Stichorchis subtriquetrus, 50.8%; Trichostrongylus sp., 36.5%; and Gongylonema sp., 11.1%. The unknown Trichostrongylus species is probably a new host record, while the Gongylonema sp. confirms a tentative description by another researcher in 1916 who speculated on the description of another researcher from an 1896 report.

The 63 beaver surveyed were infected with at least one helminth, with a mean number of worms per infection of 220.49 (±67.52). Infections ranged between 8 and 837 helminths.

The combined number of helminths per infection decreased with age; the sex had little effect, except for S. subtriquetrus where the rate was slightly greater in females (59%) than in males (42%). The 1½ to 3 year old beaver appear to have higher mean numbers of worms per infection with T. americanus and C. castoris than do younger or older hosts. Gongylonema sp. Was more prevalent in older beaver where they had a greater mean number of worms. The males and females of the helminth occurred in the esophagus of the beaver embedded parallel to each other in zipper-like burrows which caused severe irritation of the mucosal lining. Gonglyonema sp. Appeared to be the only helminth which had obvious pathology connected with its presence in beaver.