Lethocerus deyrollei is a species of giant water bug (family Belostomatidae) that traditionally is included in the genus Lethocerus, although recent authorities places it in the Kirkaldyia. They are large (4.8–6.5 cm or 1.9–2.6 in long), predatory and nocturnal insects. They are one of the best known giant water bugs and are found in Japan, Korea, east China, east Indochina and the Amur region of Russia. They are very common in much of their range, but have declined drastically in some regions and are considered threatened in Japan. They live in still waters with vegetation, hatching in the summer months and then overwintering half a year later as adults. They primarily feed on small fish, amphibians and aquatic insects, but have also been recorded taking water snakes and young turtles. The eggs of this species are laid out of water, generally on vegetation. Males exhibit parental care by keeping eggs damp. This is achieved by climbing up to the egg mass and having the water drip off their bodies onto the eggs. Eggs that are not kept damp in this way fail to hatch.