Back Swimmer (Genus Notonecta), Santa Cruz Island, Channel Islands National Park, California. Back swimmers are aquatic insects capable of diving and remaining underwater for up to six hours. They are predators of other aquatic arthropods and small vertebrates. In the photograph a hydra has become tangled with the backswimmer and may become prey. This view is looking down on the insect as it floats inverted just below the surface with the tip of its abdomen raised for breathing.