As the most diverse and abundant group of animals on the planet, insects have colonized most of Earth's habitats. While their ubiquity in terrestrial habitats is self-evident to anyone who takes a stroll outside, thousands of species spend at least part of their lives in the water. Toe biters, water boatmen and whirligig beetles are some of the best-known insects that swim underwater.
Though some aquatic insect larvae use gills to breathe, many aquatic insects bring air with them when they submerge. Thousands of microscopic hairs cover the bodies of these insects. These hairs create a water-repellent coating on their shell, so when the insects submerge themselves, an air bubble forms around them. In this manner, the bugs are free to breathe the oxygen in the bubble and stay underwater. As the oxygen level falls and the carbon dioxide level rises inside the bubble, fresh oxygen is drawn from the water and carbon dioxide dissolves into the water. Essentially, the insect could stay underwater indefinitely.
Flying Insect Larvae
Thousands of species of flying insects deposit their eggs in the water. When these eggs hatch, the larval form is aquatic for some time before metamorphosizing into a flying adult. Many larvae are very small and look like wiggling worms moving in the water column. These insects move about by flexing their body back and forth. Mosquitos, midges and flies of the order Diptera produce such aquatic larvae, which become adults in a matter of weeks. Other insects like mayflies (Ephemeroptera) produce large larvae that remain underwater for a long period before transforming into adults. Not all aquatic larvae are strong swimmers; caddis flies (Trichoptera) attach themselves to rocks and sticks and swim very little, while others such as dragonflies (Odonta) produce larvae that crawl underwater more than they swim.
Named for their habit of occasionally biting the toes of swimmers, naturalists usually refer to these insects as giant water bugs (Belostomatidae). Though the bite is generally harmless, some people experience great pain and swelling following a bite from one of these large insects. These fearsome predators consume virtually any small animal that they can capture, including animals as large as fish and tadpoles. Though some tropical species attain four inches in length, North American species are smaller.
Water boatmen (Notonecta glauca) are sometimes called backswimmers because they swim upside down, on their backs. Hunting primarily by ambush, water boatmen generally wait motionless on the surface of the water until prey is detected. The tiny predator then quickly swims near the prey and attacks. Like all true bugs, the water boatman has a mouth adapted to piercing and sucking. In this species, the mouth is a very short beak, which delivers toxic saliva that helps to incapacitate its prey.
Whirligig beetles are the fastest swimmers of the insect world. Though they spend most of their time swimming on the surface of the water, these beetles dive quickly to capture their insect prey. Whirligig beetles primarily use their back legs to propel them through the water, while their middle pair of legs are used to steer. They use their powerful front legs for grasping prey.
- NY Times: Come Up for Air? Not These Insects, Which Carry a Bubble as a Lung
- Arkive: Water Boatman
- University of Minnesota: Guide to Aquatic Invertebrates of the Upper Midwest
- Popular Mechanics: Secrets of the Fastest Insect Swimmer
- North Carolina State University: A Class of Distinction
- CSIRO: Diptera: Flies and Mosquitos
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