Any one of numerous species of beetles belonging to Gyrinus and allied genera. The body is firm, oval or boatlike in form, and usually dark colored with a bronzelike luster. These beetles live mostly on the surface of water, and move about with great celerity in a gyrating, or circular, manner, but they are also able to dive and swim rapidly. The larva is aquatic. Called also weaver, whirlwig, and whirlwig beetle.