To capture their prey, giant water bugs typically use ambush tactics. They hide in aquatic vegetation and wait for something to pass them by. When something comes too close, the powerful forelegs snatch it and keep it still as the giant water bug eats it, similar to how a praying mantis catches its prey. It eats by thrusting its rostrum (reminiscent of a syringe) into a soft area and injecting paralysing and digestive juices into its meal. These begin to liquefy its prey until the giant water bug can suck it up through its mouthparts.
It can take a long time to eat a meal this way, especially if the prey is large. And giant water bugs can take down big prey: bugs in the sub-family Lethocerinae are known to eat fish, frogs, snakes and turtles (seen left). There are even reports of one catching and eating a woodpecker!
Unsurprisingly, they can deliver a nasty bite. Though there are no known long-term effects (a relief considering their saliva liquefies and paralyzes tissues), the short-term pain is horrendous. It has been described as "burning" and "intense, excruciating pain", sometimes followed by a temporary loss of touch and sensation. One study in 2010 notes that no treatment has been found to be effective so far.
Photo: Japanese species Kirkaldyia deyrolli (sub-family: Lethocerinae, family: Belostomatidae) eating a baby turtle. Credit to Dr. S. Ohba.