The lice, Haffneria grandis and Saemundssonia were extracted from their hosts, skuas (Aves: Stercorariidae). Lice were extracted from dead birds by combing feathers, while lice from live birds were extracted using a delousing chamber containing chloroform vapour. Lice were measured and the data analysed by canonical discriminant analysis. Lice show variation in morphology that is useful in identifying some of these hosts. This variation is presumably due to micro-environmental pressure provided by each host. Our interpretation is that these chewing lice have evolved to be adapted to each skua taxon; different sizes and morphologies of skua taxa result in different sizes and morphologies of Haffneria grandis and Saemundssonia.