Any of you scuba divers? And any of you ever seen any insects down there? Nope, thought not. And why? Because of maths.

Insects manage to survive under water by forming a thin bubble around themselves to trap air and let them breathe. Mathematicians John Bush and Morris Flynn at the Massachusetts Institute of Technology have looked closely at all the factors that control the stability of the bubble and have done the sums to work out the limits on the insects’ sub-aquabatics. (paper and press release)

There’s a maximum depth that insects can dive to before the bubble pops, around 30 metres. But there’s also a minimum depth above which the bubble becomes unstable.

Even though these insects, like the water boatman, could dive deep deep down, they typically don’t bother – it’s dark, cold and there’s not much to eat – but plenty of things to eat them.

The bubble has to have a large surface area, for gas exchange, allowing the insects to breathe. The tiny hairs coating the insects’ tummy are crucial for this. Too close and the bubble is tough, but too small. Too far apart and it becomes fragile and the insect would, well, drown, Bush and Flynn say.

Apparently, researchers elsewhere are investigating this bubble design for humans, but to get enough oxygen a surface are covering over 100 metres would be needed. Doesn’t seem quite practical. Think I’ll leave it to the insects, bzzzzz.

Image: John Bush and Morris Flynn/MIT