The influence of substrate type on the drift and colonization patterns of Hydropsyche larvae (Trichoptera: Hydropsychidae) in a Michigan stream.

Drift and colonization patterns in Hydropsyche spp. was observed in various substrate types in the Maple River, Michigan. Experiments in colonization using pie pans found a significant difference among substrate types, particularly between Cladophora-covered and bare substrates. Sheer stresses on the animal or potential predation pressure were explored as possible reasons for the patterns observed, but no significant results were obtained for those hypotheses. The architectural significance of Cladophora was imitated using thread attached to bare rocks, but no significant difference was found in colonization patterns among the bare and string-attached cobbles. A study of drift in enclosures set up in various reaches of the Maple River found that hydropsychid drift is positively correlated with the percentage of gravel in any given reach. These results as well as their implications for the population dynamics of Hydropsyche spp. are addressed.