Architectural plasticity in net construction by individual caddisfly larvae (Trichoptera: Hydropsychidae)

Abstract

Multiple nets spun in different water velocities were collected from individual hydropsychid caddisfly larvae (Hydropsyche and Cheumatopsyche) in a flow tank. Mesh size (coarseness) decreased and the total area of the regular meshes of the net increased with increasing ambient velocity for nets spun by individual Hydropsyche larvae but not for those spun by individual Cheumatopsyche larvae in the range of velocities used (0.05–0.45 m/s). The functional significance of these observed structural changes for both particle capture rate and silk stress was evaluated theoretically on the basis of mechanical principles. The structural changes seen in faster water are predicted to increase the particle capture rate by about 75% and the stress in the silk of the net by about 25%. These increases due to structural changes are small compared with the predicted 25-fold increases in particle capture rate and stress due solely to experiencing faster water. The changes in construction do suggest that a greater investment of silk and spinning time is made by larvae in faster water, and this is also demonstrated by the greater proportion of nets that were spun in faster water.