Understriped diving beetle

Description

Understriped diving beetle is a large water beetle. It occurs in the Unites States from Maine to Minnesota south to Virginia and Missouri, and in adjacent Canadian provinces. It also occurs in western Canada from Alberta to the Yukon, and in Wyoming. It is found in permanent ponds and marshes with sedges. The larvae, called water tigers, are more often among aquatic plants, while the adults are more often in open, deeper water. Both larvae and adults are voracious eaters, preying on aquatic invertebrates and small fish. Larvae also prey on mosquito larvae in the spring.

Adults are ⅞″ to 1⅛″ (22.0 to 27.9 mm) in length. The body is elongated oval, broadest near the middle, and it is streamlined, convex both above and below. It is usually brown or brownish-black, sometimes green. On the underside, the rearmost plate of the thorax (metasternum) is brownish-black in the middle. The underside of the abdomen is mostly brownish-yellow to reddish.

The exoskeletal plate covering the first segment of the thorax (pronotum) has a broad pale stripe on the lateral margin. The front margin has a narrow faint pale stripe, a narrow dark reddish stripe, or no stripe all. The rear margin is never striped. The triangular plate (scutellum) between the bases of the wing covers (elytra) is visible.

The elytra on the female always have distinct parallel groves. On the male the elytra are smooth, polished, and sparsely hairy. On both sexes they completely cover the abdomen and there is a pale stripe on each lateral margin. The stripes narrow beyond the halfway point and disappear before reaching the wingtip.

The mouthparts are directed forward. The antennae are thread-like and have eleven segments. The eyes are not notched above the antennae bases.

The rear legs are flattened and much longer than the front and middle legs. The first segment (coxa) of the hind legs is yellow. The fourth segment (tibia) has two spurs at the tip. The smaller spur is as wide or only slightly wider than the larger spur. The last part of the leg (tarsus), corresponding to the foot, has five segments. On the hind legs, the rear margins of the first four tarsal segments are bare, not fringed with golden hairs. The outer margins of each segment are covered with hairs which aid in swimming. On the front legs of the male, the first three tarsal segments are greatly widened, and together form a nearly circular suction disk.

Size

⅞″ to 1⅛″ (22.0 to 27.9 mm)

Similar Species

Habitat

Permanent ponds and marshes with sedges

Ecology

Season

One generation per year: April to November

Behavior

Adults are very good swimmers. They will come to lights.

Life Cycle

Adults overwinter in permanent waters. They mate in late fall or early spring. The male uses the suction disks on its front legs to hold the female while mating.

Larva Food/Hosts

Mosquito larvae, aquatic invertebrates, and small fish

Adult Food

Aquatic invertebrates and small fish