Black-spotted Falsehorn

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.

Flowers: Elderberry (Sambucus sp.)

Temnostoma excentrica – Lake Metigoshe State Park, ND – June 12, 2016

Eastern Hornet Fly

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.

Eastern Catkin Fly

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.

Flight season: April – May

Flowers: Catkins?

Similar species: Chalcosyrphus inarmatus

Brachypalpus oarus
Brachypalpus oarus (male) – Rice County – April 17, 2017