Papallacta stenoptera (Diptera: Dolichopodidae) gen. n. & sp. n. is from described from mossy paramo habitat at 4000 m in Ecuador. This species is tiny, body length 1.3 mm, has the wing reduced to a narrow strap, and is the first stenopterous dolichopodid described from the New World. Based on the structure of the head, thorax, and male postabdomen, and the setation, Papallacta belongs in the Medeterinae, even though males have large obovate aristal flags, unusual in this subfamily. Ant predation is regarded as a factor limiting the occurrence of flightlessness in Diptera.