Forewing length 7 to 10 mm. Shiny black with white markings similar to the interjectus form of A. albifrons, but the head is black, not white.

Streams, rivers and lakes.

May to August.

Throughout England, Wales and mainland Scotland, but not common in south eastern England.

Possibly locally frequent, but under recorded in Leicestershire and Rutland. Recorded at Woodbrook when it was particularly numerous (>11,000) in 1990. Also at four widely distributed river sites, as larvae, during the river surveys of 1986.