THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Dytiscidae are a diverse, beautiful, and interesting group of beetles, about which surprisingly little is known. They are commonly found in a wide variety of aquatic habitats with still waters and abundant vegetation, including wetlands. Both larvae and adults must return to the surface of the water to obtain oxygen; adults can trap air beneath their elytra and use this supply underwater. As their common name suggests, they prey on a variety of macroinvertebrates, as well as on amphibians and fish, earning the fierce larvae the additional title of "water tiger."

Adults have oval streamlined bodies; a scutellum may be visible, and the front legs lack tibial spurs. Their antennae are relatively long and slender. Hind legs are flattened, oar-like, and fringed with long swimming hairs. They are strong fliers and will take to the air regularly, but because of their modified legs, they cannot land easily. They generally hit the water like raindrops, then return to the surface to get air.

The larvae have elongated bodies that taper strongly towards the tip of the abdomen, which may end in two small tails. They have thin legs, and prominent curved mandibles on the front of the head. These mandibles are hollow; the larva uses them to latch on to prey, and then injects digestive juices through them and sucks up the liquified contents of the prey.

Size: small to xlarge
Identifying feature(s): simple antennae, the last 3 segments of which are not swollen to form a club
Habitat: mostly still waters; wetlands
Tolerance to pollutants: tolerant