Tarsal movements in flies during leg attachment and detachment on a smooth substrate.

In order to understand the attachment mechanism of flies, it is important to clarify the question of how the adhesive pad (pulvillus) builds and breaks the contact with the substrate. By using normal and high-speed video recordings, the present study revealed that pulvilli are positioned on the surface in a particular way. The pulvilli are apparently loaded or pressed upon the substrate after leg contact, as evidenced by splaying of the claws. Detachment of pulvilli from the substrate may be achieved in four different modes depending on the leg (fore-, mid- or hindleg): pulling, shifting, twisting, and lifting. Lifting is the only detachment mode depending on the claws' action. Kinematics of the tarsal chain is studied in leg preparations, in which the tendon of the claw flexor muscle was pulled by tweezers and video recorded. The morphological background of tarsal movements during attachment and detachment is studied by scanning electron microscopy, fluorescent microscopy, and bright field light microscopy followed by serial semithin sectioning of pretarsal structures. Several resilin-bearing springs are involved in the recoil of the tarsal segments to their initial position, when the tendon is released after pull.