bee-mimic robber flies

Laphria index and Laphria ithypyga are two very similar, small to medium-sized, robber flies. Both species occur in the eastern half of the United States and southern Canada. They cannot be told apart in most photos, only in those that clearly show the genital bulb of the male. For this reason, they are sometimes treated as a species complex called Laphria index complex.

Laphria index is much more common and is the only species that has been recorded in Minnesota. Cedar Creek Ecosystem Science Reserve has both species on their Checklist of Minnesota Insects, but it does not have a record for either species.

Adults are found in woodland edges and openings from mid-May to mid-August. The larvae live in the soil or in rotting wood, where they prey on the larvae of other insects.

Adults are dark, slender, and ½″ to 11 ⁄16″ (12 to 18 mm) long.

There is a narrow triangle of golden hairs on the thorax. The triangle is widest at the rear.

The first two abdominal segments are black with white hairs on the side. Segments 3 through 6 are densely covered with orangish-gold hairs. On the male, at the rear margin of segment six, there are two black, well-defined projections. The genital bulb at the tip of the abdomen is black and very large.

Laphria index and Laphria ithypyga are distinguished by the size of the genital bulb and by the projection(s) at the end of abdominal segment 6.

Sources

7, 24, 27, 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.

Few of the North American Laphria species have a common name. One common name for the genus is bee-mimic robber fly, and it is applied here for convenience.

Laphria index or ithypyga bee like robberfly black with gold hairs

Picture was taken in the hedgerow next to Barnes Prairie, Racine Co., Wisconsin on June 20, 2021.

This medium size robber fly flew from tree to tree, landing on the trunks of the trees. Per BugGuide, species ID is unlikely to be determined from photographs.

Location: Barnes Prairie, Racine Co., Wisconsin

Picture was taken in the hedgerow next to Barnes Prairie, Racine Co., Wisconsin on June 20, 2021.

This medium size robber fly flew from tree to tree, landing on the trunks of the trees. Per BugGuide, species ID is unlikely to be determined from photographs.

Location: Woodbury, Minnesota