Water beetles - Dytiscidae family

Dytiscidae water beetle family overview

The beetle below is Dytiscus marginalis, the great water beetle or carnivorous water beetle, a member of the Dytiscidae family. There are 4000 species world wide in this family, some up to 7 cm long. There are 118 species in the UK, where they range in length from 0.2 cm to 5.0 cm. Both larva and adult are carnivorous, and the UK species have jaws powerful enough to puncture human skin. The fossil record for the Dytiscidae goes back as far as the Jurassic.

All the adults in this family have the same oval-shaped body and fringed and flattened hind legs, which makes them powerful swimmers. Their air supply is carried under their hard fore wings (elytra), and they stick the tip of their abdomen out of the water to take in air. Usually the adults emerge in the late summer or early autumn. Pupation takes place out of the water. The larva (below) digs a chamber in the bank. In the summer pupation can take just 2 or 3 weeks, but in the autumn or winter the adult will not emerge until the spring.