Feeding rate, the rate of movement of food through the gut and gut morphology of large larvae of five caddis species (Halesus radiatus, Hydropsyche instabilis, Polycentropus kingi, Rhyacophila dorsalis and Potamophylax cingulatus) were investigated in the laboratory. Following 72 hr starvation, P. cingulatus and H. radiatus larvae became satiated (refused prey offered directly to the mouthparts) after consuming 8-11 and 9-13 mayfly nymphs (Baetis rhodani, 3.5-4.6 mm) respectively. Hunger level affected prey consumption. In P. cingulatus, the number of prey consumed over 24 h (at 9.5-12-degrees-C) increased with starvation periods from 0-72 h, but declined following longer starvation periods.Six clearly recognisable gut states (defined by the position of food material in various parts of the gut) can be identified at different times since commencement of a meal. As environmental temperature increased (from 8-12-degrees-C to 15-17-degrees-C), the rate of change of the gut state increased and the food retention time decreased in all species. Feeding periodicity (i.e. nocturnal/diurnal activity) in the field was estimated based on the evacuation rate and the gut state and environmental temperature at the known time of collection. Initiation of consumption of prey appeared to coincide with emptying of the foregut and proximal midgut, whereas actual feeding continued until complete satiation when some threshold' fullness of the foregut had been reached. The length of time food was held in the foregut was positively correlated with increasing specialisation of the foregut (particularly elaboration of the proventriculus).