Came across this big group of individuals swimming around in a small stream in Coorg. They could easily have been mistaken for a school of fish and I did too. However, they seemed to be swimming on the water’s surface, with the upper half of their bodies outside, unlike most fish. Looking closely, realized that they weren’t fish at all, but a completely different kind of creatures. They were insects, more specifically, beetles.
These beetles are more popularly known as the Whirligig beetles. They get this name from the way they whirl around rapidly in circles when threatened, as if caught in a whirlpool.
Whirligig beetles belong to the ‘Gyrinidae’ family of water beetles. They do have wings like most other beetles and are very much capable of flying. However, these are preferential water denizens. Having a nicely lubricated outer layer, hind legs modified to aid in swimming and a pair of split eyes, one part above the surface of water and the other below, enabling them to see both sides at the same time, these beetles are very well adapted for their marine lifestyle.
Adults are capable of carrying an air bubble, which help them breathe underwater as well. They also seem to be a very social group of insects, living and moving around in large groups, having an added benefit of evading predators.
These beetles feed on debris that float around on the surface of water and also on any struggling insect or other small invertebrates that might fall in. Whirligigs’ have developed an amazing way of hunting its prey. They are attracted to the waves caused by the struggling victim and as a group they start honing on to it. Once honed in, they start biting nibbles off it.
They seem to employ some sort of simple Radar for this. The water ripples are the medium used to send messages here, as in the image below.
When the whirligigs detect the waves from a struggling insect that has fallen into the water, they start their rapid spinning action, sending ripples across the water’s surface. These water ripples bounce back from the victim. This light echo is detected by the whirligigs and they use this information to triangulate the location of their prey. How cool is that !!
They are also very beneficial insects. As scavengers they help in cleaning the water of dead and decaying matter.
All in all, it was lovely having seen these wonderful group of insects. These seem to have pioneered technologies that we humans have very recently been able to develop !