Giant Water Bugs, Family Belostomatidae

Habits and Traits of Giant Water Bugs

Giant water bug with eggs on its back.
Giant water bug males carry and care for their offspring. Getty Images/PhotoLibrary/John Cancalosi

There's a reason members of the family Belostomatidae are called giants. The giant water bugs include the biggest insects in their entire order. North American species can reach 2.5 inches long, but the size record for this family belongs to a South American species that measures a full 4 inches in length at maturity. These hulking Hemipterans lurk below the surface of ponds and lakes, where they're known to nip at the toes of unsuspecting waders.

Description:

Giant water bugs go by a number of different nicknames. They're called toe biters for their habit of sampling people's feet (which I assure you, is a startling and painful experience). Some call them electric light bugs, because as adults these winged behemoths can and do fly, and will show up around porch lights during mating season. Others call them fish killers. In Florida, people sometimes call them alligator ticks.

Whatever you choose to call them, the family of giant water bugs shares certain morphological traits. Their bodies are oval and elongate in shape, and appear flattened. They have raptorial front legs, made for grasping prey, with thick femora. Giant water bugs have short heads, and even shorter antennae, which are tucked beneath the eyes. A beak, or rostrum, folds under the head, just as in terrestrial true bugs, like assassin bugs. They breathe by means of two small appendages at the end of the abdomen, which function like siphons.

Classification:

Kingdom – Animalia
Phylum – Arthropoda
Class – Insecta
Order – Hemiptera
Family - Belostomatidae

Diet:

A giant water bug eats just what you would expect a large, predaceous, aquatic insect to eat: other insects, tadpoles, small fish, and snails. They don't limit their meals to organisms smaller than they are, either.

Giant water bugs can overpower critters several times their size with their strong, grasping forelegs. According to some sources, giant water bugs have even been known to capture and consume small birds. Being true bugs, giant water bugs have piercing, sucking mouthparts. They pierce their prey, inject them with strong digestive enzymes, and then suck up the pre-digested bits.

Life Cycle:

As all true bugs do, giant water bugs undergo incomplete metamorphosis. The young emerge from their eggs looking much like miniature versions of their parents. The nymphs, which are entirely aquatic, molt and grow several times until they reach adulthood and sexual maturity.

Special Adaptations and Behaviors:

Perhaps the most fascinating thing about giant water bugs is the way they care for their offspring. In some genera (Belostoma and Abedus), the female deposits her eggs on her mate's back. The male giant water bug is tasked with caring for the eggs until they hatch in 1-2 weeks. During this time, he protects them from predators, and regularly brings them to the surface for oxygen. He will also move to stir up the water around his body, keeping it oxygenated. In other species (genus Lethocerus), the mated female deposits her eggs on aquatic vegetation, above the water line.

But males still play a role in their care. The male will usually stay submerged near the plant's stem, and will periodically climb out of the water and wet the eggs with water from his body.

Giant water bugs are also known to play dead when threatened, a behavior is known as thanatosis. If you happen to scoop up a giant water bug in a dip net while exploring your local pond, don't be fooled! That dead water bug might just wake up and bite you.

Range and Distribution:

Giant water bugs number about 160 species worldwide, but only 19 species inhabit the U.S. and Canada. Throughout their range, giant water bugs live in ponds, lakes, and even drainage ditches.

Sources:

  • Borror and DeLong's Introduction to the Study of Insects, 7th edition, by Charles A. Triplehorn and Norman F. Johnson.
  • Guide to Aquatic Insects and Crustaceans, Izaak Walton League of America.