By Daniel Cressey of Nature magazine
Beetles have an impressive ability to walk underwater. It is all down to tiny bubbles trapped between hair-like structures on their feet.
The insects are often observed clinging tenaciously to smooth surfaces such as leaves, hanging on even when those surfaces are vertical. Naoe Hosoda, a materials scientists at the National Institute for Material Science in Tsukuba, Japan, and Stanislav Gorb, who studies biomechanics at the University of Kiel in Germany, have now shown that beetles can even keep their footing underwater.
On land, leaf beetles (Gastrophysa viridula) secrete fluid into hair-like structures called setae on their feet. Forces exerted by the setae and the fluid keep the insects attached to surfaces that they are walking on, but such forces don't usually act in water. However, Hosoda and Gorb found that when the beetles walk on flooded surfaces, bubbles of air are trapped in the setae. The bubbles themselves provide adhesion, but they may also de-wet the area around the beetles’ feet to allow the ‘hairs’ to function in the same way as they do in the dry, the researchers report in Proceedings of the Royal Society B.
Hosoda and Gorb also observed other beetles walking underwater, such as the ladybird shown in the video above.
Inspired by the beetles, the researchers developed a polymer structure covered in bristles that mimic the beetles' feet. Attached to small objects — such as the treads of a toy bulldozer — it successfully stuck them to vertical surfaces underwater.