Yellow-throated Wasp-mimic Flower Fly
Identification: Note: Northern Ontario C. pubescens sometimes have white marks, not yellow.
Head: Upper face black with a grayish pile spot on each side above antenna base on female, eyes wide apart. Male has light yellow V-shape above antenna, eyes touching each other to simple eyes (ocelli). Top of head black, with long yellow hair. Eyes have pile. Lower face yellow with black stripe down middle from antenna base to mouth area.
Black stripe at lower eye margin separates face from underside or cheeks. Underside or cheeks has extensive pale yellow (i.e. Yellow-throated).
Antenna: Shiny black, long. 1st joint short, 2nd joint 1.5 times as long as 1st, 3rd joint as long as 1 and 2 combined.
Thorax: Black, covered with sparse, long yellow hair, including sides (longer on female). Segment 1 (scutum) has obvious, longitudinal grayish pile stripes down middle, one each side of centre, may be faint or absent on male. Slightly interrupted, wide yellow stripe on side edges. Segment 2 (scutellum) yellow with a dark center, may be faded. Thorax side has large yellow patch. Main ID: A smaller pale yellow spot below the large patch, sometimes touching, a 2nd small spot close to head across from large patch. Two more small spots each side of wing base. Main connection ring to abdomen entirely yellow (difficult to see, and sometimes considered segment 1 of abdomen).
Wings: Slightly tinted, outer edge and base light brownish-yellow. Base cell (bm) completely filled with pile. Halteres reddish-yellow.
Legs: Yellow. Hind thigh (femur) more reddish-yellow on last half. Feet more reddish-yellow.
Abdomen: All segments with scant covering of erect, yellow hair; segments over-lap each other, so side edges of abdomen appear jagged or serrated. Segment 1 all black. All following segments have yellow arched stripes starting at lower outside edge of segment, arching to near base of segment at center, and interrupted at center. The lower edge of each segment where the stripe starts and the base of next segment is directly below it, have an tiny reddish-orange blotch (i.e. on outside ‘corners’). Also, lower margin of segments has a slightly lighter yellow stripe, thicker at centre, and increasing in thickness progressively on each segment to tip. Segment 5 is narrower and sometimes described as an inverted black Y or V shape because the lower border stripe is very thick and extends between the arched stripes.
Underside black with long yellow hair. Lower margin of underside segments has V-shaped dashes at side edges. Segments 2 to 4 also have semi-circular spots at mid segment, each progressively smaller to tip. Segment 5 black.
Similar Species: Chrysotoxum flavifrons has only one large yellow spot on thorax side (Blackshield). Top of thorax has some black hair mixed in with the yellow. Wings have much darker brownish outside border. Main connection ring to abdomen is black; underside of abdomen does not have large spots at mid segment.
Chrysotoxum derivatum has much thinner abdominal stripes.
Size: 12 to 15 mm
Habitat: Forests and edges of forests.
Food: Flowers from a variety of plants, shrubs and trees.
Flight Time: June to September
Life Cycle: Apparently larvae (and cocoons) are moist soil dwellers and feed on aphids and/or ants; larvae 11 mm long, 5 mm wide, cylindrical, white. Pupa pale yellow. Pupate in spring.
Comments: Essex County – Ojibway Prairies, Windsor. Kent County – Rondeau Provincial Park. Also Bruce Peninsula, Hamilton, Kingston areas and Quebec.
For information on synonyms, references and type specimens see next page