Thirty-two trials using these artificial substrates, a flow tank, Hydropsyche and Cheumatopsyche, were run, with one type of substrate used per trial (10 caddisflies were allowed 1.5 hours to build retreats, and then their positions were mapped). The hypothesis that decreased substrate complexity would lead to caddisflies using the substrate's perimeter more than its interior was verified (p < 0.001, Chi-square).  In all, 79 caddisflies used the perimeter. Of these, 52 were near the tank sides instead of the downstream screen. Caddisfly movement towards the stream edges seemed to exceed caddisfly drift.