How insects breathe underwater

MIT mathematicians have learned more about how insects breathe underwater by trapping a layer of air around their bodies. The scientists determined that insects can dive as deep as 30 meters without the bubbles bursting. (Seen here, a Notonecta covered with a respiratory bubble.) From MIT News Office:

Newsoffice 2008 Underwater-1-EnlargedThe air bubble's stability is maintained by hairs on the insects' abdomen, which help repel water from the surface. The hairs, along with a waxy surface coating, prevent water from flooding the spiracles--tiny breathing holes on the abdomen.

The spacing of these hairs is critically important: The closer together the hairs, the greater the mechanical stability and the more pressure the bubble can withstand before collapsing.

However, mechanical stability comes at a cost. If the hairs are too close together, there is not enough surface area through which to breathe....

"Because the bubble acts as an external lung, its surface area must be sufficiently large to facilitate the exchange of gases," said (study co-author Morris) Flynn, who is now an assistant professor of mechanical engineering at the University of Alberta. Other researchers have explored systems that could replicate the external lung on a larger scale, for possible use by diving humans. A team at Nottingham Trent University showed that a porous cavity surrounded by water-repellent material is supplied with oxygen by the thin air layer on its surface. The surface area required to support human respiration is impractically large, in excess of 100 square meters; however, other avenues for technological application exist. For example, such a device could supply the oxygen needed by fuel cells to power small autonomous underwater vehicles.