Abstract: The excellent crawling and attachment abilities of insects strongly depend on their attachment devices. As the attachment devices of insects are morphologically different, they can be divided into two major groups, either hairy or smooth. Both of them can contact with almost all known surfaces via adhesive fluid, irrespective of whether the surface is rough or smooth, and the contact between the two types of adhesive pads and the substrate is operated by van der Waals forces. In this article, we reviewed the progress in the adhesion mechanisms of insect legs including the structures of the hairy and smooth adhesive pads and their adhesion mechanisms, and the functions, compositions and releasing mechanisms of the adhesive pad secretion. We also illustrated how insects resolve the contradictions between firm attachment and rapid detachment movements of adhesive pads of their legs, and discussed the influence of environmental factors such as physicochemical properties of the contact substrate and environmental humidity on insect adhension, aiming to help deeply understand the adhesion mechanisms of insect legs and to provide theoretical basis for its application in bionics.

Key words: Insect, leg, adhesive pad, setae, secretion