variable duskyface fly

Variable duskyface fly is a small, common and widespread, typical hover fly. It occurs in Europe, Asia, North Africa, and North America. In the United States it occurs in the east from Maine to Maryland, west to Minnesota and Iowa, and south along the Appalachian Mountains to northern Georgia. In the west, it occurs on the West Coast from northern Washington to southern California. It occurs across southern Canada from Nova Scotia to British Columbia, and north along the West Coast to Alaska.

Variable duskyface fly is one of the most abundant hoverflies in North America. Melanostoma mellinum is undoubtedly a complex of multiple species. However, standard DNA barcoding using the COI gene is misleading and it will not help to resolve the issue. A recent molecular DNA study (Haarto & Ståhls, 2014) used the ITS2 marker to successfully differentiate Melanostoma species in northern Europe. Until a similar study is conducted for North America, Melanostoma mellinum will remain the only species in the genus that is recognized on the continent.

Adults are active from late April to early October. They are found in grasslands, clearings and roadsides in woodlands, pastures, farmlands, parks, and suburban gardens. They feed on flower nectar and pollen. The larvae prey on at least 32 species of aphids and gall-forming psyllids in leaf litter and on the ground layer.

Adults are 3⁄16″ to ⅜″ (4.8 to 10.0 mm) in length. The body is slender, the face is entirely black on both sexes, and the abdominal markings on both the male and female are distinctive.

On the male, the head is brownish-black, hemispherical, and wider than the thorax. It is strongly concave in back and closely appressed to the thorax. The back of the head (occiput) is very narrow. It has dark hairs above and pale hairs on the sides. There are two large compound eyes on the sides of the head and three small simple eyes (ocelli) in a triangle on top of the head. The compound eyes are bare, with no hairs, and they meet at the top of the head. The ocellar triangle is covered with dark hairs. The face is shiny. The only part of the forehead (frons) that is visible between the eyes is called the frontal triangle. There is gray dusting on the cheeks, thin gray dusting on the ocellar triangle, and thin or indistinct gray dusting on the frontal triangle and the face. The protruding mouthpart (proboscis) is short and fleshy. The antennae are mostly dark brown and short, shorter than the head. They have three segments. On the third segment there is usually a yellow spot on the underside near the base, and there is a stiff, forward-pointing bristle (arista) near the tip. The arista is bare, not feather-like (plumose).

The thorax is large, and it has three segments. Each segment has four principal exoskeletal plates, one above, one below, and one on each side. The upper (dorsal) plates, from front to rear, are the prescutum, scutum, and scutellum. The scutum is shiny and brownish black and there is gray dusting at the front margin. It is covered with short, erect, mostly pale hairs. On each side of the scutum, in the shoulder (humeral) area just behind the head, there is a small plate (postpronotum). The postpronotum is bare, with no hairs or bristles. Unfortunately, this is not visible without first removing the fly’s head. The scutellum is shiny and brownish black. The plates on the sides of the thorax are brownish black and mostly hairless. The lower front plate of the middle segment (katepisternum) has an upper and a lower patch of hairs. The upper and lower patches are widely separated. There is gray dusting at the front margin of the scutum, and there is usually thin gray dusting on the sides of the thorax.

The abdomen is nearly parallel sided and 2 to 5 times as long as wide. It has five visible segments (tergites). Segments two through four (T2 to T4) have a pair of large, yellow, rectangular spots.

The legs are slender. On all legs, the first segment (coxa) is black, the second segment (trochanter) is dark brown, the third segment (femur) is mostly black, yellow just at the tip, and the fourth segment (tibia) is yellow with a dark brown ring. The last part of the leg (tarsus), corresponding to the foot, is mostly dark brown. On the middle legs, the last two tarsal segments are yellow.

The wings are clear. The entire wing surface is usually covered with minute hairs (microtrichose).

On the female, the occiput usually has both pale and dark hairs above. The frons is black and shiny, and there is a pair of grayish dusted triangles near the top. The triangles are moderate sized, broadest at the side, and narrowing to the middle. They do not meet in the middle. The abdomen is oval to nearly parallel sided and 2 to 4 times as long as wide. Segments two through four (T2 to T4) have a pair of large, yellow, inverted triangular-oval spots.

Total length: 3⁄16″ to ⅜″ (4.8 to 10.0 mm)

Grasslands, clearings and roadsides in woodlands, pastures, farmlands, parks, and suburban gardens

Late April to early October

Aphids

Flower pollen and nectar

Sources

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

Telford, Horace S.. (1939). The Syrphidae of Minnesota. University of Minnesota. Minnesota Agricultural Experiment Station.

Abundant

Melanostoma mellinum Variable Duskyface Fly

Melanostoma millennium, Variable Duskyface Fly, at Barnes Prairie Remnant, photographed on June 22, 2024.

Melanostoma mellinum
Lloyd-Davies

Melanostoma mellinum on the Prairie Orchard August 23, 2014
The Prairie Orchard

VARIABLE DUSKYFACE, Melanostoma mellinum in web
Rob Curtis

Hover Fly on the flower | Melanostoma mellinum
Shalika Dhananjaya Photography

Babette Kis
6/22/2024

Location: Barnes Prairie Remnant, Racine Co., WI

Melanostoma millennium, Variable Duskyface Fly, at Barnes Prairie Remnant, photographed on June 22, 2024.