The occurrence of gapeworm (Syngamus trachea) in willow grouse.

21.4% of the willow grouse (Lagopus lagopus) examined from a coastal locality in northern Norway were infected with Syngamus trachea. None of the willow grouse examined from an inland locality with colder and longer winters were infected with the parasite. It is suggested that the parasite may influence survival of the grouse population.