robber flies

Cerotainia is a genus of very small robber flies. There are more than 30 Cerotainia species worldwide. two species in North America north of Mexico, and 2 species in Minnesota.

Cerotainia adults are found from mid-June to mid-September in meadows and fields and at forest edges. They are usually encountered perched at the tips of leaves and grass blades. They feed on small flies and other insects. They fly out to capture passing prey and often return to the same perch.

Two North American species are generally recognized, but the number of species in North America is a matter of debate. One species, Cerotainia macrocera, with brown eyes and black and white hairs, is relatively common in the eastern United States but rare in Canada. A second species, Cerotainia albipilosa, with green eyes and much more white hairs, is reported as common in Canada, but some consider it a color morph of Cerotainia macrocera, not a distinct species. A third species, Cerotainia atrata, has been described from a single specimen in Nebraska in 1907. It has never been found again, and the specimen is now classified as an unrecognized species.

Cerotainia adults are black and 3 ⁄16″ to ⅜″ (5 to 9 mm) in length.

The compound eyes are widely separated at the top. When viewed from the side the entire face protrudes beyond the eyes. The forehead (frons) is covered with long hairs. The antennae are relatively long. The first segment (scape) is four or more times as long as the second segment (pedicel).

The wings are clear. They are smoky brown at the tip, becoming paler at the base. The first and second branches of the radial sector vein (R₁ and R₂₊₃) join before the end of R₁ creating a closed cell that does not reach the margin.

Sources

29, 30, 82, 83.

The superfamily Asiloidea was formerly placed in Orthorrhapha, one of two infraorders of Brachycera, a suborder of Diptera. However, Brachycera did not contain all of the descendants of the last common ancestor (paraphyletic). It was split into five extant (still existing) and one extinct infraorder. Orthorrhapha is now considered obsolete and has not been used in decades, but it persists in printed literature and on some online sources. A recent revision of the order Diptera (Pope, et al., 2011) revived the name Orthorrhapha, but this has not been widely accepted.

This genus has no common name. The common name of the family Asilidae is robber flies, and it is used here for convenience.

Cerotainia sp. robberfly

Cerotainia sp., robberfly, with prey, on Barnes Prairie, Racine Co., WI. Photographed on July 11, 2021.

Location: Barnes Prairie, Racine Co., WI

Cerotainia sp., robberfly, with prey, on Barnes Prairie, Racine Co., WI. Photographed on July 11, 2021.