The Lonchaeids are small flies with a black or blackish-blue body, which is often metallic, glossy, and with hyaline (lacking dark spots) wings. The head is hemispherical (shorter than high) and the lunule is well defined. The third antennal segment is usually elongated and the antennae are decumbent. Ocelli are present and the postocellar bristles are divergent. The frons is narrow in males; in females it is broad. One pair of orbital bristles is on the head. The postvertical bristles on the head are parallel or weakly divergent. Distinctive vibrissae on the head are lacking, but vibrissa-like bristles are present along the border of the mouth. A subapical bristle is absent on tibia. The wing venation is complete. The costa has two interruptions: near the humeral crossvein and before the subcostal vein. The subcostal vein varies in size. The anal vein of the wing is shortened. The abdomen is oval and rather flat, and in females has a long, sclerotized ovipositor. The ovipositor is rather long and triangular.