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Genus Toxomerus

Syrphid - Toxomerus geminatus - female 5008769 syrphid - Toxomerus geminatus - female Syrphid Fly - Toxomerus boscii - male Wide flies - Toxomerus occidentalis - male - female Hover Fly - Toxomerus geminatus Toxomerus geminatus - female Toxomerus marginatus - male Syrphid Fly - Toxomerus occidentalis
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon ("Aschiza")
Family Syrphidae (Syrphid Flies)
Subfamily Syrphinae
Tribe Toxomerini
Genus Toxomerus
Synonyms and other taxonomic changes
Toxomerus Macquart, 1855
Mesogramma Loew, 1866
Mesograpta Loew, 1872
Explanation of Names
Toxomerus Macquart 1855
From Greek toxon 'bow' + meron 'thigh' (refers to the bow-shaped hind femur)
Numbers
14 spp. in our area(1)(2)(3)
Size
5-13 mm
Identification
Pattern on abdomen is characteristic(4); look for a v-shaped notch on the back margin of the eye.
In identifying the most common eastern 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, T. geminatus (scutellum dark with sharp yellow border) or T. politus (scutellum light). --Steve Pelikan
Guide to common spp.:

Further south, esp. 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.
"extremely diverse in the tropics with many, many undescribed species and over 100 described species. In Florida, there are 10 species of Toxomerus: T. arcifer, T. boscii, T. corbis, T. dispar, T. floralis, T. jussiaeae, T. geminatus, T. parvulus, T. politus and T. marginatus. It is necessary to see characters on the hind leg of the male, a good lateral view, and wing microhairs to identify Florida specimens to species." --Jeff Skevington
Range
Holarctic
T. marginatus: much of the US & so. Canada; common
T. geminatus: e. NA; common
T. politus: so. Canada to Argentina; uncommon
T. occidentalis: w. NA; common
10 spp. in Florida
Life Cycle
Eggs are laid singly on plants near aphids. Presumably late-instar larvae overwinter. Pupation is in soil cavities in spring; adults emerge in summer.(4)
Egg laying
See Also
Print References
Borges, Z. M. and M. S. Couri. (2009). Revision of Toxomerus Macquart, 1855 (Diptera: Syrphidae) from Brazil with synonymic notes, identification key to the species and description of three new species. Zootaxa, Vol. 2179, No. 1: 1-72. (Zootaxa)
Miranda, G. F. G, Young, A. D., Locke, M. M., Marshall, S. A., Skevington, J. H., Thompson, F. C. 2013. Key to the Genera of Nearctic Syrphidae. Canadian Journal of Arthropod Identification No. 23, 23 August, 2013. Available online at doi: 10.3752/cjai.2013.23 (1).
Stone, A., C. W. Sabrosky, W. W. Wirth, R. H. Foote, and J. R. Coulson. A Catalog of the Diptera of America North of Mexico. Agriculture Handbook No. 276, United States Department of Agriculture, 1696 pp. (3)
Thompson, F.C. (1981). The flower flies of the West Indies (Diptera: Syrphidae). Memoirs of the Entomological Society of Washington, Vol. 9: 4–200. (Smithsonian Libraries DSpace Repository)
Vockeroth, J. R. (1992). The insects and arachnids of Canada. Part 18. The flower flies of the subfamily Syrphinae of Canada, Alaska and Greenland. Agriculture Canada, Ottawa, 456 pp (5). (Government of Canada)
Internet References
Works Cited
1.Key to the genera of nearctic Syrphidae
Miranda G.F.G, Young A.D., Locke M.M., Marshall S.A., Skevington J.H., Thompson F.C. 2013. Can. J. Arthropod Identification 23: 1-351.
2.Toxomerus mutuus
3.A Catalog of the Diptera of America North of Mexico
Alan Stone, et al. 1965. United States Department of Agriculture.
4.National Audubon Society Field Guide to Insects and Spiders
Lorus and Margery Milne. 1980. Knopf.
5.The flower flies of the subfamily Syrphinae of Canada, Alaska, and Greenland, Diptera: Syrphidae
Vockeroth J.R. 1992. The insects and arachnids of Canada, Pt. 18. Ottawa: Agriculture Canada. 456 pp.