The whirligig beetles (Gyrinidae) are a family of water-dwelling, small to medium-sized beetles that normally live on the water surface (neuston) of stagnant waters or quiet streams. They can be often observed as groups, rapidly swimming in circles and zig-zag, especially when alarmed. The middle and hind legs are transformed into highly specialized natatorial legs. Worldwide about 800 species have been described, in Germany 13 species are known to occur. They are predators of insects that live in or have fallen into the water. Determination by photo without specimen is impossible. In Germany Gyrinus substriatus is by far the most common species.