Microhabitat Characteristics of Hydropsyche (Trichoptera:Hydropsychidae) and the Importance of Body Size

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Abstract
The effects of sedimentation, microhabitat velocity and flow patterns, and larval body size on the distribution of four species of net-spinning hydropsychid caddisflies (i.e., Hydropsyche betteni, H. sparna, H. cheilonis, and H. bronta) were examined in Jordan Creek, Illinois. Significantly more larvae occurred in hydraulically calibrated concrete artificial substrate notches with little or no sedimentation. Accumulation of sediment did not appear to adversely affect the larvae during the study, however, because no significant differences were found between the distributions of larvae and the distributions of notches among four categories of sedimentation. Most larvae were found inhabiting microhabitats with rapidly spiralling flow vortices reflecting the importance of microhabitat flow pattern on Hydropsyche larval distribution. No significant differences were found in the distributions of the four species among the microhabitat velocities inhabited, although some fifth-instar H. betteni, the largest of the four species studied, were found inhabiting velocities up to 35 cm/s, whereas the other species were restricted to velocities less than 25 cm/s. Within a species, larger larvae were found at higher velocities than smaller, less mature, larvae. These results suggest that larval body size and microhabitat flow pattern, rather than capture-net mesh size, influence the distribution of Hydropsyche larvae in Jordan Creek.

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