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Family Overview
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.
Characteristics
POLLUTION TOLERANCE
Mid-Atlantic: up to 5
Midwest: 4.1 - 7.9
Southeast: 1.8 - 10
0 = least tolerant, 10 = most tolerant
FEEDING HABITS
Engulfer / Predator
MOVEMENT
Diver
Swimmer
Diagnostic Characters
+ Expanded Character List
Order: Adults with hardened forewings (elytra) covering the hind wings. 
Family: Ventrally, pronotum with conspicuous curved lines near each lateral margin (notopleural sutures). Metasternum without transverse sutures. Elytra covering entire abdomen or exposing only part of 1 tergite. Hind coxae each with median portion extending in posterior direction, dividing abdominal segment 1 into lateral sclerites, but not expanding into broad plates. Without large spur on end of each front tibia. Dyticidae without broad wedge-like hind coxal plate. Scutellum usually visible; if hidden, then front and middle tarsi apparently 4-segmented and hind tarsi each with 1 claw. Hind tarsi and usually tibiae flattened, streamlined, and bearing long, stiff swimming bristles. Body usually 3–25 mm long.