Synonyms and other taxonomic changes
Explanation of Names
Probably from Greek platys (πλατυς)- "broad, flat" + cheir (χειρ)- "hand, arm"
Numbers
Nearctica lists almost 80 species.
Identification
Small to moderately large Syrphid flies. The abdomen is black, marked with yellow or grey spots, leaving the abdomen anywhere between black and almost yellow.
Most of the time only males can be IDed, you need a good shot of the forelegs. Dorsal habitus always helps too, as you can narrow down possible species a lot just by color/body shape.
A few of the common species are easy though: P. quadratus males have broadened mid tibia that are quite distinct (most Platycheirus have only broadened foretibia, if any).
P. obscurus is very silvery, with a produced face covered in pruniose ripples. P. obscurus and P. confuscus can be tricky to tell apart from a photo, but obscurus's face is more produced, with the oral margin extending beyond the tubercle, whereas confuscus usually has the tubercle extending beyond the oral margin.
Having a specimen is usually invaluable. (Comments by Andrew Young)
Range
The genus is predominantly boreomontane in distribution, occurring in arctic regions and on high altitude parts of the Alps, Carpathians etc. Some have a circumboreal distribution.
Habitat
They live in grass and herb vegetation.
Season
Many stay active during cold and rainy weather and some conjecture that lower temperatures are optimal for this genus.
Food
The adults of many species feed on pollen of wind-pollinated plants, such as Salix, Plantago, Poaceae, Cyperaceae, but they visit also other flowers, e.g. Ranunculus (visited by P. occultus) or Umbellifers (visited by P. peltatus).
Larvae feed on aphids.
Remarks
They are rather inconspicous in the field, both because of the small, slender and often blackish appearance and because they tend to remain hidden in the vegetation. They share these features with the genus Melanostoma, a closely allied genus. Catching the flies often includes sweeping the net through the vegetation. A field of Plantago may reveal many Platycheirus flies of several species!
Print References
Vockeroth, J.R. 1990. Revision of the Nearctic species of Platycheirus. Canadian Entomologist, 122: 659-766.
