Digenean flukes can be broadly classified into three basic groups according to their location within the host: (1) the lumen of the alimentary canal or associated organ, (2) body cavity or tissue and (3) external surfaces. We selected three species of Proterometra that represent these basic groups and tested their capacities for cutaneous transport of glucose. Facilitated diffusion is the type of transport system in the tegument of P. edneyi, which lives in the gut of its host. An active transport system is present in P. dickermani, the tissue-dwelling species. No cutaneous system for transporting glucose is present in the ectoparasitic P. macrostoma. The known capacities for tegumental sugar transport in other digeneans are correlated with similar habitats. Such associations involving unrelated as well as closely related species suggest that the niche biology of digeneans involves evolutionary specializations of the tegument for absorbing sugar.