Trichacantha atranupta family Athericidae
Quoted from: Field guide to South African Insects
"Members of this small, rather primitive, family resembles small horseflies with large, often smoky wings. Adults are found on rocks or vegetation alongside fast-flowing streams, where the aquatic larvae are predators. The region has the richest athericid fauna in the world, with at least 16 species in 3 genera.”
The hind legs are greatly enlarged and elongated.
Males (shown here) have a black patch on each wing while the females are small and a darkish brown.