Lethocerus deyrollei is a species of giant water bug that traditionally is included in the genus Lethocerus, although recent authorities place it in the monotypic Kirkaldyia. They are large, predatory and nocturnal insects. They are one of the best known giant water bugs and are found in India, 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 and Korea. 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.