Fluid Flow through Filtering Appendages of Insects

Abstract

Many organisms use structures composed of arrays of cylinders to capture particulate food or molecules form the water or air around them. The performance of such filters depends on the velocity of fluid movement through them; hence, mathematical models of flow through fibrous structures can provide insights about the functional morphology of biological filters. In this paper, the authors address the case of feather-like biological filters of finite width and assess several possible models for fluid motion through them by comparing model predictions with observational data. Two examples of insect appendages are considered: the cephalic fans of black fly aquatic larvae that capture particulate food and the antennae of adult male moths that catch sex-attractant molecules released by female moths. The results suggest that flow through such structures can be much slower than ambient currents, that the finest hairs in the structure are the morphological features with the greatest effect on leakiness, and that the velocity of movement (or of ambient flow), as well as the morphology of such filters, can be critical in determining their performance.

moth, black fly, filter feeding, pheromone, flow, porous plate, low Reynolds number