Acoustic microscopic analysis of the biological structure of insect wing membranes with emphasis on their waxy surface

The mechanical performance of natural materials depends on the type, and especially the composition of the molecular constituents. They are almost without exception composite materials, whose characteristics are determined by the charakteristics of the individual constituents, their shape, their interaction, and in particular their orientation within the natural material. One of the most impressive natural composites is the insect cuticle. This lightweight building material impresses one with ist ability to withstand extremely heavy loading. Even the ultrathin (3-10 µm) membranes of insect wings add greatly to the structural stability of the wings. By means of acoustic microscopy, the present study also shows that the thin covering of wax on the membrane is not an accidental material arrangement. Contrary to that of locust wings, dragonfly wing membranes were found to have a criss-cross fiber-like density gradient within to the waxy layer. This density gradient proved to be mechanically relevant in stabilizing the wings