Giant water bugs are the largest insect that lives underwater. Excluding Hokkaido, it is found in various locations of Japan. It is also found in China, Taiwan, and the KoreanPeninsula. It can grow up to be 6 cm to 7 cm in length.

It waits in the bushes of water grass for its prey to pass by and captures small fish and even frogs with its large front legs. Once captured, the giant water bug stabs it with its mouth, injects digestive fluid, and melts the prey from the inside and sucks in until only skins and bones are left.

From June to August, you can often see male giant water bug protecting and spraying water on eggs laid on pickets. Larvae molt 5 times within a month after hatching and become an adult.

Before the war, giant water bugs were found in most paddy fields but due to the effects of agricultural chemicals, it is rare to find them in recent years. It is listed on the red list as a 2nd class endangered species by the Ministry of Environment.