Movement patterns and foraging ecology of a stream caddisfly larva

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Abstract
The movement patterns and time–activity budgets of Dicosmoecus gilvipes were quantified from underwater observations of marked individuals in a northern California stream, during two studies in early and late June, 1977. Individuals traveled several metres per day. The only striking differences between the observed patterns of movement and those predicted from a random walk model are the following: (a) in both studies, large larvae moved significantly farther than small larvae; (b) in both studies, there is a pronounced diel rhythm to movement, with animals traveling faster during the day; (c) rates of travel in late June are ~3 times faster than those in early June. Since more than two-thirds of the total time–activity budget of these larval insects is dedicated to feeding, we suggest that the patterns of movement reported here largely reflect activities related to food acquisition. Several observations indicate that food is locally limiting and heterogeneously distributed across the stream bottom, thus requiring animals to move from patch to patch in order to meet their food requirements. Seasonal differences in rates of movement appear to result from phenological changes in the quantitative and qualitative food requirements of these stream insect grazers.