Wednesday, April 6, 2011

Predacious Diving Beetle

This large diving beetle, about 30 mm long, is out of it's element and doesn't want to pose for a picture. Mating occurs in the spring or fall, which is when these insects tend to be found flying, as this one was, between ponds or streams often some distance from water.

Definitely genus Dytiscus, probably fasciventris, the Understriped Diving Beetle, and the grooved elytra indicate it's a female. As its name suggests both the larvae (a.k.a. "water tigers") and adults are carnivorous and are large enough to capture and eat small fish and tadpoles in addition to other aquatic insects.

The bottom view also identifies this specimen as a female. The tarsi on the forelegs of male Dytiscid beetles are greatly enlarged and possess suction cups to grip the the streamlined pronotum or elytra of the female during mating. (Too bad, even if I had a male specimen, I can't get an image of the underside of its forelegs .. Laurie! I miss your digital microscope!)

Speaking of steamlining, underside of this beetle is an excellent study in adaptation to its liquid habitat. The ventral surface is sculpted with shallow pockets to accommodate the first four legs when they are are folded. And even the legs themselves are shaped so that when swimming with them tucked in their notches, the insect presents an almost seamless oval profile to minimize drag.