Wasp-mimic Flower Fly
Head: Face projecting; yellow with a longitudinal dark stripe down middle. Eyes very large, striped yellow and black, with some black spots on the yellow. Top of head black, wider on female. Mouth reddish-brown.
On female, the yellow with dark stripe extends above antenna.
On male, there is a small amount of lighter yellow above antenna, but no dark stripe and eyes are close together.
Antenna: Brownish, last segment slightly darker. Bristle (arista) yellowish, as long as antenna.
Thorax: Black. Segment 1 (scutum) with two large yellow spots on each side at base. Sometimes a small yellow spot just before each wing base. Wide yellow stripe on each side, curving to near centre. Two small yellow curved stripes at center of segment end. Segment 2 (scutellum) black with yellow curved line on lower margin. Thorax sides have 5 large yellow spots and one small one below wing base.
Wings: Half clear, outer half light reddish-brown and narrowing toward tips. Veins reddish-brown. Halteres light brown.
Legs: Thighs (femora) yellow, brown spot at tip of front thigh. Front shin (tibia) black, base yellow. Mid and hind shins yellow, tips slightly darker, hind shin sometimes with darker streaks. Front feet (tarsi) black, toes yellow. Mid and hind feet brownish-yellow.
Abdomen: Black, with yellow down side edges of abdomen. Segments 2, 3 and 4 have 2 bright yellow stripes, one near base of segment and one at segment end. Stripes are slightly interrupted at center. Segment 1 very short and entirely black. Segment 2 base stripe very wide at side edges.
Segment 5 has very thin yellow line along base of segment and is covered with brownish erect hair. Underside yellow with wide black stripe down middle of all segments.
Similar Species: Similar to Spilomyia alcimus which has a yellow abdomen with thin brown stripes. Head and thorax almost identical.
Size: 11 to 15 mm
Habitat: Forests and woods edges.
Food: Nectar from Goldenrod and Asters.
Flight Time: August to mid-October.
Life Cycle: Larvae have been found in tree holes between 2 and 8 metres high in living trees, including Black Oak Quercus velutina and Maple Acer. Classed as ‘deep rotholes’ by Copeland (Gr. Lakes Ento, 1989), the holes are filled with liquids from the tree’s sap system and retain a dark reddish-brown color all season. These holes stay wet and do not require rainfall to replenish them. Larvae have 4 pairs of spines and apparently feed on wet areas along the walls of the deep rotholes. Larvae probably feed on rotting organic matter.
Comments: Essex County – Point Pelee. Kent County – Rondeau Provincial Park. Also Bruce Peninsula, Toronto area and Cambridge. Wheatley, 2004 to 2013, females only, always on goldenrod or aster.
In Ontario, these flower flies mimic worker Yellowjacket hornets, and wave their black front legs, imitating the Yellowjacket’s long antenna.
For information on synonyms, references and type specimens see next page