The largest of all insect orders, the beetles include over 4000 known species with aquatic or semiaquatic life histories. Larvae can exhibit highly variable body shapes and variably hardened heads, but they generally exhibit distinct heads with chewing mouthparts, poorly developed eyes, three pairs of well-developed legs, and one to two tarsalclaws at the end of each leg. As holometabolous insects that undergo complete metamorphosis into winged adults, young beetles lack the visible wing pads seen in the nymphs of animals like stoneflies, mayflies, or dragonflies. Water beetle larvae may sometimes exhibit lateral filaments on the abdomen, but these will never end in a single long filament like the alderfly or hooks like the dobsonfly.
No pollution tolerance categories defined.
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.
Lateral Gills USUALLY Absent
Three Pairs of Legs on Thorax
USUALLY 4-5-Segmented Legs
+ Expanded Character List
Larvae: Usually without lateral abdominal gills. If gills present, then 4 hooks clustered on segment 10. Thoracic legs each usually with 4 or 5 segments and with 1 or 2 claws; if without legs, head distinctly sclerotized and posterior body (thorax and abdomen) simple, without gills, hair brushes, suckers, or breathing tube. Eye spots usually present, but compound eyes absent.
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