* Japanese name: Gamushi
* Scientific name: Hydrophilus acuminatus
* Description: Adapted for aquatic life, water beetles have streamlined bodies and heads. Despite this, they are not powerful swimmers, having normal legs that are not flattened like oars for swimming. Most of their lives are spent crawling on aquatic plants. They are dark green to brown (or even black) in color, but the body is covered with fine hairs that trap a thin layer of air, giving them a silvery appearance underwater.
* Where to find them: Lakes and ponds from Hokkaido to Kyushu. Water beetles are one of the few insects that are active year round.
* Food: Adults are mainly vegetarian, feeding on aquatic plants, except when breeding, when they will eat other aquatic animals such as small fish and tadpoles. Larvae are carnivorous.
* Special features: The Japanese name (ga) refers to a tooth or spine on the underside of the adult's body. This can inflict a nasty wound on a predator attempting to eat the beetle -- or on the finger of a human attempting to catch it. The larvae, too, have special defense systems. They often play dead if a predator is nearby, and if they are surprised they release a black pigment into the water. Under the cover of this "smoke screen," they can make their escape -- or launch a counterattack. Adult beetles carry a bubble of air under their elytra (wing case), like a scuba tank. Most water beetles come up to the water surface tail-first, but silver water beetles raise their heads first, breaking through the tough surface layer with specially adapted hairy antennae. The water-repellent antennae hairs trap air, channeling it down from the surface into the scuba tank to replenish the beetle's reservoir. When females lay eggs, they first make protective cases from the leaves of aquatic plants floating on the water surface. The eggs are laid into the cases, where they are safe from harm.