A guide to the Flower Flies (Syrphidae) of Minnesota
Author: Scott King
A writer and citizen scientist, I currently live in Northfield, Minnesota. Three recent books are Following the Earth Around: Journal of a Naturalist's Year, Brevities, and Rice County Odonata Journal: Volume Four.
The Yellow-spotted Sapeater (Brachyopa vacua) is a small, brown Nearctic species. The thorax is gray with purplish overtones. Segment two of the abdomen is almost entirely yellow, while segment three has small spots of yellow on the anterior corners. Goggle-eyed, slightly irregular in shape, the eyes sweep forward along the produced face. Most specimens have been found at elm tree wounds. The flies are observed hovering in front of the wound, perched adjacent to the flow of sap, or ovipositing directly into the flowing sap. The larvae feed on the sap and live in the wounds.Field notes: The bi-colored abdomen visible through the folded wings, at first glance, creates the illusion that the wings are banded.
Flight Dates: June
Flowers: Adults are most commonly observed at flowing wounds on elm trees, but they have occasionally been observed at flowers, including Goats Beard, Dogwood, and Cow Parsnip.
Similar species: Most similar to other Brachyopa species. Also could be confused with Hammerschmidtia rufa.
Field Notes: The bi-colored abdomen visible through the folded wings, at first glance, creates the illusion that the wings are banded.
The White-bowed Smoothwing (Scaeva pyrastri) is a medium-sized, black-and-white, Holarctic flower fly. The oval abdomen has paired white markings that are curved like parentheses and which do not reach the abdomen margin. The coloration of this species sets it apart from nearly all other species in the Syrphinae which have yellow markings. The r4+5 vein is not straight but has a noticeable, upward curve. The larvae are entomophagous, consuming mostly aphids. One study reported a single larva consuming close to 500 aphids.
Flight Dates: June
Flowers: Tends to prefer blue flowers. Has been observed on Blue Flax (Linum lewisii) in Minnesota
Similar species: Scaeva selenitica which has yellowish markings instead of white and Eupeodes volucris , a western, montane species, which differs in having a straighter r4+5 vein.
Field Notes: This species is thought to be a migrant in Europe. Also, rarely, a melanistic form, without the characteristic white spots on the abdomen, has been observed.
The Back-spotted Falsehorn (Temnostoma excentrica) is a large, yellow-and-black, Nearctic flower fly. A convincing Yellowjacket Wasp (Vespinae) mimic. In addition to being a visual mimic, this fly (and the other Falsehorns) lift and wave their black forefeet in front of their heads, imitating the antennae of wasps. Markings on thorax are whitish-gray in color. Paired yellow bands enclose a pair of black, rectangular spots on the 4th and 5th abdomen segments (open on segments 2 and 3). In the north, the abdominal markings can be white instead of yellow, mimicking the Bald-faced Hornet (Dolichovespula maculata).
Larvae found in decaying wood
Flight season: June
Similar species: Temnostoma alternans, Spilomyia alcimus, Spilomyia fusca, Somula decora, and Sphecomyia vittata, which are all yellowjacket mimics.
The Eastern Hornet Fly (Spilomyia longicornis) is a large, yellow-and-black, Nearctic flower fly. A convincing wasp mimic. In addition to being a visual mimic, the Eastern Hornet Fly mimics the behavior of wasps as well, wagging its abdomen up and down, flicking its wings, and waving its dark-colored front legs as if they were long antennae. The unusual eye coloration and patterning, dark spots and blotches overlaying a light background, is characteristic of this species and other species in this genus. Larvae are dendrolimnetobionts, obligate rot-hole inhabitants.
Flight season: August and September
Flowers: More often observed perched on leaves at the edge of woods rather than at flowers, however, it is known to visit asters and goldenrods.
Similar species: Spilomyia alcimus, Somula decora, Sphecomyia vittata, and Temnostoma alternans, which are all yellowjacket mimics.
Field notes: There exists a curious intersection here, between language and mimicry, as the species name “longicornis” refers to the Longhorn Beetles. My guess is that Loew, who assigned the name in 1872, had the Locust Borer in mind, a beetle that has a somewhat similar yellow-banding pattern. Expressed in terms of what it is not, the name draws attention to the convergent evolution of mimicry.
The Common Bog Fly (Parhelophilus laetus) is a medium-sized, orange-colored, Nearctic flower fly. Adults have a pair of stripes on the thorax often with a thin center stripe between them. The hind femur is mostly orange with a black band around the middle. The adults are commonly found perched on grass blades near the shorelines of ponds and wetlands. The larvae have long breathing tubes which allow them to live in low-oxygen waters thick with decaying organic matter.
The Dusky Bog Fly (Parhelophilus rex) is a medium-sized, dark-colored, Nearctic flower fly. Adults have a pair of thin gray stripes on the thorax. The hind femur is almost entirely black. The larvae have long breathing tubes which allow them to live in low-oxygen waters thick with decaying organic matter.
Flight season May – July
Flowers: Willow catkins
Similar species: Parhelophilus obsoletus and Helophilus sp.
The Eastern Catkin Fly (Brachypalpus oarus) is a large, infrequently-observed, Nearctic flower fly of old woodlands. Usually observed hovering near or perched on sunlit tree trunks. An imperfect mimic of large mining bees. When perched on a tree it resembles robber flies of the genus Laphria. The body is covered with long, yellowish hairs. The face of the female is triangular in shape. The larvae live in rot holes in deciduous trees. Length 10 – 14 mm.