Insects use trapped oxygen to breathe underwater

Hundreds of insect species spend much of their time underwater, where food may be more plentiful. MIT mathematicians have now figured out exactly how those insects breathe underwater.

By virtue of their rough, water-repellent coat, when submerged these insects trap a thin layer of air on their bodies. These bubbles not only serve as a finite oxygen store, but also allow the insects to absorb oxygen from the surrounding water. The insects use this bubble as a kind of external lung.

Thanks to those air bubbles, insects can stay below the surface indefinitely and dive as deep as about 100 feet. Some species, such as Neoplea striola, which are native to New England, hibernate underwater all winter long.

The 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.