Genus Platycheirus

Pyrophaena is treated as a separate genus here, following(1)(2)

Platycheirus Lepeletier & Serville 1828

Greek platys (πλατυς) 'flat' + cheir (χειρ) 'hand'

73 spp. in our area, ~220 spp. worldwide(2)(3)

Body length 4.7-10.5 mm (4)

Usually 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)

predominantly holarctic boreomontane (~2/3 of our fauna occur in NT-AK): arctic regions and high altitudes in the Alps, Carpathians, etc. Some have a circumboreal distribution. ~30 spp. are known from high altitudes in Taiwan, Nepal, the Philippines, and New Zealand.(2)

grass and herb vegetation

Many stay active during cold and rainy weather and some conjecture that lower temperatures are optimal for this genus.

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.

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!