The adult is about 6 to 9 mm long and has bluish black wings which have a characteristic fold at the distal extremity, making the rear of the wing look very angular when viewed fom above. They are called 'longhorn' because of their antennae which are threadlike and extremely long, approximately twice the length of the body. The males have distinctly larger eyes than the females and have distinctive large and hairy maxillary palps used in mating.

Mystacides nigra - matt black wings.

Streams, rivers, canals lakes and large ponds. Probably best seen when males aggregate in swarms above the water surface of lakes and slowly running water for mating.

May to September.

M. azurea performs a swarming flight with vertical zig zag movements. A female, when approaching a swarm, is caught by a male which holds her around the abdomen with its long maxillary palps and both use their wings to fly in tandem to the shore where they copulate. The aquatic stages are found in shallow marginal areas of lakes and ponds or in the slowly moving tracts of streams. They are omnivorous feeding on plant detritus as well as other arthropods.

Quite common and widespread in Britain

Fairly frequent in Leicestershire and Rutland.