Burrowing behavior and biogenic structures of mud-dwelling insects

Little is known about the burrows of sediment-dwelling insects because these structures are concealed by the sediment in which the animals live. We used X-ray images to reveal and compare the burrowing behavior in the laboratory of aquatic insects from several orders (Diptera, Ephemeroptera, Megaloptera, Trichoptera). Most of the taxa studied constructed U-shaped burrows. Exceptionally, individual caddisfly larvae (Polycentropus sp.) varied greatly in the type of burrow they constructed, i.e., I-, J- and U-shaped burrows were observed. Most taxa begin new burrows from preexisting ones under the sediment surface, obviating the need for the animals to leave the sediment and thereby minimizing their exposure to potential predators. Nymphs of the mayfly Hexagenia limbata exceeded all of the other taxa studied in terms of the depth and length of their burrows and their burrowing rate. Our data suggest that nymphs of H, limbata could be responsible for 98% of the volume of sediment disturbed by littoral insects in our study lake. Observations on 3 species of Chironomus suggest that the rate of burrow construction can differ among congeners. Individuals of H. limbata and Sialis velata burrowed to greater depth in the autumn than in the spring. Our study illustrates the potential of radiographs to study the behavior of burrowing animals, and the range of variability in burrowing behaviors among genera and species of insects.