The following item is reprinted from Nature research highlights 14 October 2004. (October 14, 2004)

Biophysics
Flies get a grip
 

Proc. R. Soc. Lond. B doi:10.1098/rspb.2004.2850 (2004)

How does the fly that's been annoying you by crawling up your window manage to hold on? A study of fly footprints shows that the offending insect relies mainly on capillary forces generated by fluid secreted from its feet.

Mattias Langer et al. used atomic-force microscopy to examine the adhesiveness of tiny puddles of foot fluid left by a fly, Calliphora vicina, as it walked across a glass slide. As the fluid evaporates, its stickiness decreases, showing that the fluid plays an important role in generating adhesion between foot and substrate. Adhesion measured in air was much stronger than that measured in an aqueous environment, indicating that capillary forces are mainly involved in the fly's attachment mechanism.

Electron-microscopic examination of the fly's feet supports this theory. The attachment pads at the end of the insect's legs are covered with tiny bristles called setae, each ending in a spatula-shaped terminal plate. Coated with fluid secreted from the centre of the attachment pad and delivered through a channel to the terminal plate, the plate is perfectly shaped to form a contact with the substrate through this capillary bridge.

Michael Hopkin