bumble bee mimic robber fly

Uncommon

Late May through July

Woodland edges

Laphria thoracica 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 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 radius veins (R₁ and R₂₊₃) join before the end of R₁ creating a closed cell that does not reach the margin.

Beetle larvae

Bees and beetles

Larvae are borers in moist, dead wood.

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.

Sources: 7, 24, 27, 29, 30.

No Common Name
Few of the North American Laphria species have a common name. The common name for the genus is bee-like robber fly. Laphria thoracica is one of several species known for being a bumble bee mimic, so “bumble bee mimic robber fly” will stand in for the common name.

Location: Woodbury, Minnesota