This is the largest North American family of aquatic beetles, including over 400 species in about 35 genera. Both adults and larvae can be found in almost any aquatic habitat, even in brackish water; however, they are most often found in lentic freshwater systems. The larvae tend to be climbers on rooted plants and swimmers; adults are swimmers and divers. Both larvae and adults are engulfing predators of small invertebrates and fish, and are sometimes cannibalistic. Some larvae have a channel along the inner margin of each mandible to help them ingest fluids from their prey. Their bite is quite painful. Despite living in the water, adults and larvae of most species must regularly resurface for air.
Mid-Atlantic: 5 and higher
Midwest: 4.1 - 7.9
Southeast: 1.8 - 10
Engulfer / Predator
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Order: 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.
Family: Larvae approximately 5–70 mm long. Sickle-shaped mandibles without mola (grinding surface). Long, slender swimming legs 5-segmented, excluding 2 claws. Abdomen 8-segmented, lacking hooks on terminal segment, usually without gills. Roughly cylindrical thorax and abdomen tapered to anterior and posterior ends. Cerci (urogomphi) usually 2-segmented, slender and longer than abdominal segment 1, but can be stout, short, inconspicuous, or absent.