marsh fly

not listed

NNR - Unranked

not listed

Tetanocera plebeja is a common and sometimes abundant marsh fly. It is small for a fly but medium-sized for a marsh fly. It occurs in the United States from Maine to Pennsylvania, west to Minnesota and Iowa, and there are scattered records in the west. It also occurs in southern Canada from Nova Scotia to Winnipeg. Adults are found from late May to mid-September in marshy areas near ponds and streams. They are short lived and there are multiple generations per year. The larvae are aquatic. They are parasites of gray field slug and marsh slug. They eventually kill their hosts.

Adults are ¼″ to 5⁄16″ (7.1 to 7.4 mm) in length and have a 5⁄16″ (7.6 mm) wing length.

There are two large compound eyes on the side of the head and three small simple eyes (ocelli) in a triangle on top of the head. Two bristles rise from the ocellar triangle. A distinct longitudinal band (vitta) extends from the ocellar triangle to the front margin of the forehead (frons). The vitta is broad, polished, and almost parallel sided. It is not enlarged at the front. The antennae are orange, long (for a fly), and distinctly projected forward. They have three segments. The second segment does not have a longitudinal groove (suture). When viewed from above, it is at least half as long as the third segment. The third segment has a long, bristle-like extension (arista). The arista is black and feather-like (plumose) with long and very close black hairs.

The front part of the body (mesonotum) is brownish-yellow with several longitudinal, brownish-orange stripes. On the upper side, there are two narrow stripes in the middle above (middorsal) and a bold stripe at each lateral margin. There is also a bold stripe on each side of the mesonotum. The plate between the abdomen and the thorax (scutellum) is the same color as the mesonotum and is not shiny.

The abdomen is brownish-yellow, usually with a darker longitudinal stripe in the middle and another on each side.

The wings are brownish-yellow. The entire leading edge (costal margin) beginning with the stigma is margined with blackish-brown, and that continues a little beyond the wingtip. There is a grayish streak in cell r₄₊₅, and cell m usually has a dark cloud in the center. The cross vein (r-m) near the center of the wing is short and straight. The cross vein (dm-cu) near the wingtip is long and distinctly curved, but too steeply curved to be called an S-shape. Both cross veins are margined with brownish-black. When the wings are completely closed, the cross veins of both wings taken together appear, to this writer at least, like a smiley face.

The legs are brownish-yellow. The fourth leg segment (tibia) is usually a little darker than the third segment (femur). On the middle legs, the femur has small stiff hairs (setulae) but no long bristle-like hairs (setae). On the hind legs, the fourth leg segment (tibia) has only one seta before the tip. The last part of the leg (tarsus), corresponding to the foot, has five segments. On the front legs, the first tarsal segment (basitarsus) is not paler than the basitarsus on the other legs. On all legs, the tarsi are blackened toward the tips.

Total length:¼″ to 5⁄16″ (7.1 to 7.4 mm)

Marshy areas near ponds and streams

Multiple generations per year: late May to mid-September

Pupae overwinter in leaf litter.

Gray field slug (Deroceras reticulatum) and marsh slug (Deroceras laeve)

Sources

24, 27, 29, 30, 82, 83.

This species has no common name. The common name of the family Sciomyzidae is marsh flies, and it is applied here for convenience.

Location: Albany, NY

Location: Woodbury, MN

Location: Woodbury, MN