Mystacides niger is closely related to Mystacides longicornis above. Both species belong to a family of Caddis Flies called the Long-horned Caddis Flies. And it is easy to tell why: Mystacides niger has very long antennae indeed. The lower part is ringed. Also striking are the big palps. Palps are organs on the jaws of insects and crustaceans. With some imagination they could be compared to lips of mamals. Usually they are quite small or may even be invisible without magnifying glass. But in some cases, like in Grass Moths or the Fan-foot Moths they can be very big. The palps of Mystacides niger are big, black and nearly always bent. The animal may be black (niger in the scientific name means black) the legs are light and thus very conspicuous. There is a species resembling Mystacides niger very much: Mystacides azureus. In the right light however one can tell them apart easily, for the latter has a blueish sheen, while Mystacides niger is plain black. Measuring up to 10 mm both species are quite small. Adults can be seen in spring and early summer. Males often swarm in dawn and dusk to attract females.