Length around 12 mm. A large, dark diving beetle very similar to other members of the Ilybius family.

Freshwater ponds and other still or slow flowing, well vegetated water bodies, although it flies well and can be attracted to light.

All year round but best from April to September.

Carnivorous at both the adult and larva life stages.

Widespread and fairly frequent in England and Wales. There seem to be fewer records from Scotland.

Fairly frequent in Leicestershire and Rutland. There were approximately 40 VC55 records for this species up to March 2015.