Hymenolepis microps is a well known cestode inhabiting red grouse Lagopus scoticus, blackcock Lyrurus tetrix and capercailzie Tetrao urogallus in Europe. Recently the presence of this worm in America has been recorded by Jones and in Canada by Clark. In both cases the host was the ruffed grouse, Bonasa umbellus. It is a species which is easily recognisable because it possesses a very large cirrus sac in the mature part of the worm which passes unchanged into the gravid segments. It is found in grouse in the British Isles mainly in the summer months and then it occurs in enormous numbers. When the gut is opened the strobilae appear as a thick rope, being tangled so closely that it is very difficult to obtain a complete specimen.