Explanation of Names
Author of genus is
Macquart, 1855. From Greek
toxon (τοξον) bow, plus
merus (or
meros, i.e., μερος?) femur (Internet searches, including Wiktionary--
toxic). Clearly refers to the bow-shaped hind femur.
Numbers
16 species listed in Nearctica.
Identification
Small syrphid. Note yellow stripe on sides of thorax. Pattern on abdomen is characteristic.
(1)
Look for a v-shaped notch on the back margin of the eye.
Comment from Steve Pelikan:
In identifying the most common eastern flies of the genus to species consider the margin of the abdomen. If continuously yellow (sometimes narrowly so) you've got T. marginatus. If it is alternating black and yellow because the dark horizontal bands extend all the way to the edges, consider T. geminatus and T. politus.
To separate these last two, look at the color of the scutellum. If light, T. politus; if dark with sharp yellow border, T. geminatus
See key to common species of Toxomerus:
Further south- especially in Florida- there are more species and identification from images is much more difficult (perhaps impossible)
Colors vary with overall temperature during pupation: if it was hot, the yellow/orange increases and the background becomes lighter, but if it was cold, the dark/black increases and the yellow/orange becomes darker like the background.
Range
Holarctic
T. marginatus: much of United States and southern Canada; common to abundant
T. geminatus: eastern North America only; common to abundant
T. politus: southern Canada to Argentina; uncommon to rare
T. occidentalis: western North America only; common
There are 10 species in Florida
Food
Adults take nectar and pollen. Larvae eat aphids.
Life Cycle
Eggs are laid singly on plants near aphids. Presumably late-instar larvae overwinter. Pupation is in soil cavities in spring, and adults emerge in summer.
(1)Remarks
Nearctica.com lists 16 North American species in this genus. Arnett, p. 885,
(2) lists 17 species in genus.
NCSU Entomology collection does not have an entry for this genus.
Print References
Milne, page 671, describes life history and has photograph, plate 488.
(1)Internet References
live and pinned adult images of three species with arrows pointing to diagnostic field marks (Jeff Skevington
et al, Field Guide to Flower Flies of Ontario)
USDA SEL live adult image of
T. marginatus by Mark Cassino, Michigan
Cirrus Imaging live adult images (Bruce Marlin, Illinois)
Insects of Cedar Creek, Minnesota has pinned adult images of
T. geminatus.
