Territoriality in Filter-Feeding Caddisfly Larvae: Laboratory Experiments

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Abstract
Territoriality in filter-feeding caddisflies (Hydropsychidae) was studied experimentally by providing large of Hydropsyche morosa with a limited amount of suitable substrate in laboratory streams. Distance between nearest neighbours was measured after exposing to different treatments of food concentration and current velocity for 48 hr. When suspensions of powdered Daphnia were high (50 mg dry mass/L) or were delivered by faster currents, most larval retreats were close together (no more than 3 mm apart). When food concentrations and current velocities were lower, fewer larvae were close together. In all the absence of food, most larvae were far apart (> 11 mm), including some off the substrate, at all current velocities tested. A 48-hr video recording showed that larvae without food bit and lunged at each other, mostly within the first hour of trying to establish themselves on the substrate. It appears that larvae sense food concentrations in the water, set their territory size accordingly, and vigorously defend it unless the energetic or social cost of fighting is greater than the food benefits received.

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