Whirligig Beetle - Dineutus emarginatus

TL: ~ 10 mm. Broadly oval, black beetle. Elytral apices are not finely notched. I thought it was so cool how they literally make circular-patterned waves from all their "whirligiging".

Habitat: Woodland pond

Whirligig beetles are so named because of their wild gyrations on the surface of the water. They are the only beetles that use surface tension for support. They feast on insects and produce defensive secretions from their abdomens that deter predation and alert other whirligigs to danger. What is super fascinating is that this secretion is also a water repellent that lowers surface tension so that the whirligigs can ride a wave of recoiling water molecules. The secretions smell like very potent apples...