Japan’s Predatory Giant Water Bug

Giant Water Bug Lethocerus deyrolleiPhoto: OpenCage

The giant water bug (Kirkaldyia deyrolli or Lethocerus deyrolli) became ‘big’ news in May 2011 for eating a juvenile turtle. Yet this bug is itself an endangered species. How can it be both dangerous and endangered?

The Carnivorous Giant Water Bug of Japan

This insect is a native of Japan, where it mainly lives in rice paddies by eating insect larvae, snails, small frogs, young fish and small snakes. Its bite injects some venom into its prey.

The eating of a young Reeve’s pond turtle, however, was the newsworthy incident that caught the world’s attention in May 2011.

The giant water bug grows to a length of about 15 cm (almost six inches). However, it can attack fish up to 20 cm long.

How Does the Giant Water Bug Relate to Humans?

First, it can be eaten. These are, indeed, servings of fried giant water bug. As well, the male’s pheromone ‘essence’ is an ingredient in an expensive dipping sauce.

Fried Giant Water Bug Lethocerus indicusPhoto: avlxyz

Second, this bug can bite people. The venom makes it a painful experience. This bug believes in the philosophy of ‘bite others as they may bite you’.

Third, it preys on some fish that people would farm eat.

Fourth, and most importantly, it helps control two pests. By eating freshwater snails, the giant water bug may reduce the rate of schistosomiasis infestations in both animals and humans. As well, it eats mosquito larvae and benefits people by keeping that population in check.

Is the Giant Water Bug Endangered?

Giant Water Bug Eggs and HatchlingsPhoto: hspauldi

Japan classifies this as a ‘threatened and vulnerable’ species. The role of the water scorpion, which does indeed prey upon giant water bug nymphs, has not been determined. The root cause for the ‘threatened and vulnerable’ status seems to be water pollution.

Giant Water Bug Lethocerus deyrolleiPhoto: OpenCage

Deborah Braconnier, Phys Ord, “Predator-prey role reversal as bug eats turtle“, published May 27, 2011, referenced May 27, 2011.
V. K. Thapa, IUCN Nepal, “An Inventory of Nepal’s Insects“, published 2000, PDF referenced May 27, 2011.
John L. Capinera, “Encyclopedia of entomology“, referenced May 27, 2011.
S Ohba, (S. Wellekens, editor), SpringerLink (vol 583 number 1), Abstract of “Notes on predators…of the endangered giant water bug…“, referenced May 27, 2011.