The largest of all insect orders, the beetles include over 4000 known species with aquatic or semiaquatic life histories. Adult beetles are generally hard-bodied and distinctively oval, in addition to exhibiting chewing mouthparts, well-developed eyes, and variably shaped antennae. Adults are unified by their highly modified forewings known as elytra, or the hardened, armor-like wing covers that span the abdomen, part of the thorax, and the hind wings if present. They exhibit a wide range of adaptations to aquatic life, from oarlike legs for expert swimming to air bubbles that function much like scuba tanks.
Beetles are the most diverse group of plants or animals on earth, with over 300,000 species. More than 16,000 of these species live in water for at least part of their lives. Beetles have egg, larval, pupal, and adult life stages. For different species, one or all of egg, larval, or adult life stages live in the water, but usually the pupae are terrestrial. Some larvae have slender gills for breathing underwater, others simply take oxygen through the soft cuticle or pierce stems or roots of aquatic plants. Adults do not have gills, but have various other strategies--Some hold an air bubble against breathing holes on the sides of their bodies and replenish the bubble periodically at the water surface; others maintain a thin layer of permanently trapped air over those breathing holes. Aquatic beetles can be found in water that is either flowing or still, and some even thrive in brackish environments.
Three Pairs of Legs on Thorax
+ Expanded Character List
Adults with hardened forewings (elytra) covering the hind wings.
Adult Beetle Swimming
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