Common eastern physocephala

Description

Common eastern physocephala is a medium-sized thick-headed fly. It is common in the United States from the east coast to the Midwest but mostly east of the Mississippi River. It is less common in Minnesota where it is at the western edge of its range.

At 7 ⁄16″ to ½″ long, it is a medium-sized fly but is relatively large for the genus Physocephala. With its thread-waisted body it strongly resembles a wasp, and like a wasp, it parasitizes living insects.

The head is bulbous and large, a little wider than the thorax. The top of the head (vertex) is dark brown or black. There is a narrow white line on the back of the head (occiput). There are two large compound eyes and no simple eyes (ocelli). The compound eyes are situated at the sides of the head and do not meet in the middle on either sex. The face is mostly white and prominently grooved. There is a black, fairly wide, sharply defined, T-shaped mark on the upper face (frons). The cheeks and facial grooves are black, and the facial keel is black, at least at the top. There is a very narrow silvery stripe on the face along the margin of the compound eye. The protruding mouthpart (proboscis) projects forward needle-like. It is long, straight (not elbowed), black, and conspicuously swollen at the base. The antennae have three segments. They are straight, black, and long, longer than the head, and project forward and up. The first segment is about the same length as the third. The second segment is as long as the first and third combined. The third segment is cone-shaped and has a slender, elongated process (style) at the tip.

The thorax is black and appears dusted whitish when viewed at an angle. The front angles (humeral spots) are narrow, black, and raised like shoulder pads. The balancing organs (halteres) are knob-like and yellow. The exoskeletal plate between the thorax and abdomen (scutellum) is dark brown or black.

The abdomen is black with a narrow band at the end (posterior) of each segment. The band is wider and white on segments one and two, narrower and yellowish-white on the remaining segments. The second segment and part of the third are very constricted (petiolate). Segments four through six have a white dusting above.

The legs are mostly black. The second segment (trochanter) and the base and tip of the third segment (femur) are yellowish-red. The femurs on the hind leg is irregularly thickened and is widest near the base. The fourth segment (tibia) is white on the basal half, reddish-brown on the outer (distal) half. The last part of the leg (tarsus), corresponding to a foot, has five segments. On the front and middle legs they are reddish at the base and black at the end. On the hind legs they are all black.

The forward (anterior) half of each wing is dark, the remaining is clear. The cell at the leading edge (costal cell) is usually the same dark color as adjacent cells, but is sometimes lighter or even clear. The discal cell is entirely dark and strongly indented at the first (anterior) cross-vein, which is is located well beyond the middle of the cell.

Size

Total length: 7 ⁄16″ to ½″

Similar Species

Habitat

Ecology

Season

June and July

Behavior

Adults are active during the day and are usually found on flowers.

Life Cycle

The female grasps a bumble bee in flight and forces an egg between the bee’s abdominal segments.

Larva Food/Hosts

Two-spotted bumble bee, brown-belted bumble bee, and common eastern bumble bee

Adult Food