Functional diversity of attachment and grooming leg structures is retained in all but the smallest insects

Abstract Miniaturization strongly affects functional morphology. Whereas some anatomical structures are barely affected by scaling, others can fundamentally change as the body becomes ever smaller. No prior study has focused on the effect of miniaturization on grooming and attachment structures in Hymenoptera, which can be highly diverse and complex. Through comparative description of the legs of the extremely small wasps of the families Mymaridae and Trichogrammatidae, we evaluate the functional and phylogenetic patterns concerning possible functional effects of miniaturization. On the one hand, the studied species retain some features characteristic of other Chalcidoidea, while on the other, they display some parallelisms associated with miniaturization in leg structure. These observations support a two‐stage morphocline of miniaturization, wherein the first stage is characterized by the preservation of structural complexity and retention of all basic functions, as for instance in examined Megaphragma and the females of Dicopomorpha . The second stage is characterized by a significant simplification, with the loss of redundant non‐essential functions, as observed for the males of Dicopomorpha, which have grossly reduced leg structures, including total loss cleaning devices. Whether these stages are ordered or unordered should be evaluated in future study. Functional optimization of attachment in male Dicopomorpha is indicated by the highly derived mushroom‐shaped tarsi, complemented by novel grappling spurs on the hindfeet, possibly for copulation. Our observations underline adaptive trade‐offs in the expression of complex and multifunctional leg structures at extreme scales.