Wonderful world of the whirligig

I WAS watching whirligig beetles in the margin of the canal the other day.

They are very strange creatures — in fact all water beetles are a bit odd. The whirligigs are those small, dark beetles that gather in clusters on the water surface and swim round in mad circles. They are predators and apparently swimming in circles is a way of locating prey. They catch things on the surface and below it so they have two pairs of eyes, one for seeing in water and one for seeing in air. The purpose of the whirling is to create ripples. If something like a midge lands on the water surface it alters the pattern of the ripples and the beetles sense this instantly and uses it to locate the prey.

If you disturb them they disappear under water. This is another neat trick because adult whirligigs, like all other water beetles, have no gills and have to breathe air. They manage this by grabbing a bubble of air in an organ at the tip of the abdomen and using it like a scuba diver’s tank. They can stay under water for a remarkably long time and, when they’re not whirling, this is where they hunt. But eventually they have to make a rapid trip to the surface and grab another bubble.