Comparative anatomy of pupal tarsi in caddisflies (Insecta: Trichoptera) with focus on the claw system

The decticous pupa of Trichoptera is an unusual case, as the larvae pupate in a silk cocoon under water. This leads to the problem that the pharate adult (i.e. the imago prior to eclosion within the pupal exuviae) has to cut through the cocoon and actively swim to land. To solve the latter problem, pupal legs are specifically modified. The midlegs are usually equipped with rows of hairs and are used as swimming legs to bring the insects to the water surface or the shore. Some species shed the pupal exuviae while floating on the water surface, others after crawling on stones or plants. It was assumed that this is assisted by attachment structures, especially the pupal claws. Pupal claws can differ distinctly in trichopteran lineages. However, detailed information on this character system is very limited in the literature. Furthermore, the functional principle of the pupal claw system is not well understood. Here, we present detailed data on the pupal tarsus of 15 species (14 families) using confocal laser scanning microscopy and histology. The results are discussed in terms of functional morphology, relations to larval habitat, pupal behavior, and phylogenetic implications.