eastern yellow-backed laphria

Eastern yellow-backed laphria is a large bumble bee mimic robber fly. It occurs in the United States from the northeast to the Midwest and south to Tennessee, and in adjacent Canadian provinces. There are at least 33 Laphria species in the eastern United States. Laphria thoracica is probably the most common. It is relatively uncommon in Minnesota, where it is at the western extent of its range.

Adults are robust, very hairy, and about ¾″ long. The thorax and abdomen are partially covered with long yellow hairs making it resemble a bumble bee. It is a mimic of common eastern bumble bee (Bombus impatiens), half-black bumble bee (B. vagans), and lemon cuckoo bumble bee (B. citrinus).

The thorax is stout and black. It is densely covered with long, erect, yellow hairs except for a small, round, black, bare spot in the middle. The yellow hairs extend in an arc from the front of the thorax to the side below the wing base.

The abdomen widens beyond the middle. The amount of yellow on the abdomen varies. On the female, the abdomen is entirely black. On the male, segment 1 is always black, and segments 2, 3, and 4 are often completely or partially covered with long yellow hairs.

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 upper face is covered with long, erect hairs that may be mostly yellow, mostly black, or entirely black. There is a dense mustache of long stiff bristles (mystax) on the face between the compound eyes at the lower margin, and a cluster of forward-directed bristles (a “beard”) on the lower part of the face. The mystax and beard are mostly black with a few scattered yellow hairs. The antennae have 3 segments. The third segment is elongated.

The legs are stout and black. They are covered with black hairs with patches of orange hairs. The last part of the leg (tarsus), corresponding to the foot, has five segments. The last segment has 2 pads.

On the wing, 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.

Total length: about ¾″

Woodland edges

Late May through July

It buzzes loudly when it flies. It captures its prey in flight. It uses its sharp proboscis to pierce its prey, inject enzymes which liquefy the prey’s organs, and suck out the resulting liquid.

It can deliver a painful bite when handled.

Larvae are borers in moist, dead wood.

Beetle larvae

Bees and beetles

Sources

7, 24, 27, 29, 30, 82.

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.

eastern yellow-backed laphria

Laphria thoracica bee like robberfly

Laphria thoracica, bee-like robberfly, with bumblebee prey, near the hedgerow at Barnes Prairie, Racine Co., WI. Photos taken June 29, 2020.

Laphria thoracica
Steve Collins

bee-like robber Fly (Asilidae: Laphria thoracica) Anterior View
Carl Barrentine

bee-like robber Fly (Asilidae: Laphria thoracica)
Carl Barrentine

Predators: The Watchful Robber Fly
Carl Barrentine

Up North Mom
6/9/2023

Location: Coon Rapids, MN

Found on hostas in back yard.

Location: Eden Valley, MN

Location: Barnes Prairie, Racine Co., WI

Laphria thoracica, bee-like robberfly, with bumblebee prey, near the hedgerow at Barnes Prairie, Racine Co., WI. Photos taken June 29, 2020.

Location: Woodbury, Minnesota

Location: Woodbury, Minnesota