signal fly

Rivellia is a genus of small flies in the family Platystomatidae (signal flies). There are at least 140 Rivellia species worldwide, 34 species in North America north of Mexico, and at least 14 species in Minnesota.

Rivellia adults are found on tree trunks and on foliage. They are attracted to flowers, decaying fruit, dung, and decomposing snails. Larvae are associated with the living and decaying root nodules of legumes and the roots and flowers of other plants. One species, the soybean nodule fly, has shifted from natural legume hosts to specialize in cultivated soybean crops.

Rivellia signal flies are very small, with a body length of just 1⁄16″ to ¼″ (1.8 to 6.0 mm). The genus is easy to recognize by the pattern of dark markings on the wings. Identification to the species level by photograph is difficult, sometimes relying on obscure features such as the direction of the hairs (setae) on the fourth abdominal segment.

When viewed from the side the face is concave and the back of the head is convex. The compound eyes do not meet at the top of the head on either sex. The antennae have three segments. The third segment is long and has a short, feather-like (plumose), forward-pointed bristle (arista) on the upper side. The wings are clear with four dark bands. The fourth segment (tibia) on the middle legs has a single long spur at the tip.

Sources

24, 27, 29, 30, 82.

A revision of the flies of the genus Rivellia (Otiidae, Diptera) of America north of Mexico Ryoji Namba. 1956. United States National Museum.

This genus has no common name. The common name of the family Platystomatidae is signal flies, and it is applied here for convenience.

Location: La Crescent, MN

in my backyard