stripe-legged robber fly

Stripe-legged robber fly, also called European longhorn robber, is an exotic, small to medium-sized, early season, robber fly. It is native to Europe and north Africa. The first sighting in North America was in the Boston area by Charles W. Johnson on June 28, 1916. It now occurs in the United States from Maine to Virginia, west to Minnesota and Illinois. It has also been recorded in Seattle, Washington and Denver, Colorado. It occurs in southern Canada from Nova Scotia to Ontario.

Adults are active from May to July. They are found on large shrubs at the edges of fields and forests, and in meadows, woodlands, parks, and suburbs. They feed mostly on small bees and wasps, but also on small flies and pygmy grasshoppers.

Adults are ⅜″ to 9⁄16″ (9 to 14 mm) in length. The body is slender and mostly black.

There are two large compound eyes and three small simple eyes (ocelli). The compound eyes extend above the level of the top of the head (vertex), making the head appear hollowed out between the eyes when viewed from the front. The ocelli are arranged in a triangle on a prominent rounded projection (tubercle) in the middle of the head between the compound eyes. The antennae are long and black, and they are covered with short black hairs. They have three segments. The first two project forward and they are held close together, while the third is elongated and angled outward, forming a Y-shaped structure. The lower face is covered with long, silvery, erect hairs. There are just a few white, forward-directed bristles (a “beard”) on the lower part of the face. The tube-like mouthpart (proboscis) is short and black.

The thorax is stout, humped, and black. It has three upper thoracic plates, from front to rear the pronotum, scutum, and scutellum. The pronotum is much reduced and not readily apparent. The scutum, the large middle plate, has two longitudinal grooves. It is moderately covered with short, light yellow hairs. The scutellum has a fringe of yellow hairs on the rear margin. On each side of the thorax, a conspicuous stripe of white hairs runs along the large lateral plate, the pleuron, to the base of the front legs. The balancing organs (halteres) are yellow.

On the male, the abdomen is slender, shiny, and black, and there is a narrow orange band at the rear margin of each segment. On the female, the abdomen is thicker and shorter. It is flat above, rounded and orange below.

The wings are clear and transparent. The veins are dark brown.

The legs are much less hairy and spiny than those of other robber flies. The front and middle legs are mostly orange, with a black streak on the upperside of the third segment (femur) and fourth segment (tibia). This is the feature that gives this species its common name. The hind legs are mostly black. The last part of the foot (tarsus), corresponding to the leg, has five segments. The last segment has a pair of claws and 2 pads at the tip.

Total length: ⅜″ to 9⁄16″ (9 to 14 mm)

Fields, forests, meadows, woodlands, parks, and suburbs

May to July

Mostly small bees and wasps, also small flies and pygmy grasshoppers

Sources

29, 30, 82, 83.

Infraorder
Orthorrhapha was historically 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.

Synonyms
Dioctria baumhauer is sometimes treated as a synonym of Dioctria hyalipennis, sometimes as a separate species, This is true both in North America and in Europe, where both are native. All references to Dioctria baumhauer in North America should be considered as referring to Dioctria hyalipennis.

Dioctria hyalipennis
Skrylten

Stripe-legged Robberfly, Dioctria hyalipennis, De Brand, NB, the Netherlands, 8 July 2023 (3/4)
Remco Hofland

Pędźka szklistoskrzydła - Dioctria hyalipennis cz2
jacoleko

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