Abstract
Large numbers of Limnephilidae were taken in monthly samples of invertebrate drift and benthos from Walla Brook, a small stream on Dartmoor (south-west England). Life histories of Chaetopteryx villosa, Drusus annulatus and Anabolia nervosa are described. Each species had 5 larval instars and a one-year life cycle. Young larvae of C. villosa (instars 1-3) and A. nervosa (instars 2 & 3) built cases of plant material, whereas older larvae built stony cases. Only larvae with plant cases were taken in the drift samples. Drift rates were low in most months. There was little difference between nocturnal and diurnal densities of larvae in the drift, except instar 2 of C. villosa which showed a definite nocturnal periodicity in February, March and April. Larvae of D. annulatus built cases of stones and were only taken in the drift samples during a severe spate. Imagines of C. villosa, A. nervosa and D. annulatus emerged chiefly at night. There was a definite upstream flight of imagines of C. villosa and A. nervosa. This upstream flight may partially compensate for the downstream drift of larvae.
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