Water Beetle

This Water Beetle was making interesting ripple rings on the water surface as it swam about. The sun also cast an interesting shadow on the bottom of the shallow backwater where it was swimming. The water is so shallow that the beetle stirred up a puff of mud from the bottom as it swam along the surface (you can see the mud just above the beetle).

This creature is a member of the family Gyrinidae, the whirligig beetles. There are many species of water beetles, and one cannot conclusively identify them without capturing them and looking at small features of their morphology. However, I believe this one is Dineutus carolinus, the Carolina Whirligig Beetle. They often swim in large aggregations containing several species and as many as 50,000 individuals. When they are threatened, they swim rapidly around in circles. Whirligig beetles are highly adapted to swimming about supported by the surface tension of the water and feed on insects and other arthropods (alive or dead) that are caught in the surface tension. They are very sensitive, through their specialized antennae, to vibrations in the surface of the water.

One would think that whirligig beetles would be quickly consumed by fish since they are so conspicuous. However, they are among the most accomplished swimmers in the animal kingdom; certainly they swim faster in both relative and actual speed than any other aquatic insect. They produce some noxious sesquiterpenes that fish find distasteful. This apparently provides some degree of protection. They are also able to fly and can pass from one body of water to another.