Platycheirus alpigenus

For terminology see Speight key to genera and glossary or Glossary of morphological terminology

Length

6.8–9.3 mm (0.27–0.37 in)

Head

The face is slightly produced ventrally, with the anterior oral margin extending forward. Dorsally, there is a weak median keel located between the antennal bases. The surface is densely covered in grey pollen, and the tubercle is shining and somewhat prominent. The antennae are dark, with the basal half of the arista being distinctly swollen.

Thorax

The thorax has a yellowish pleural pile, while the mesonotal pile consists of approximately half yellowish and half black. The katepisternum is sparsely grey pollinose, and the halter is dark brown. The wing has the basal two-thirds of cells c and bm bare, with the apical quarter of the cup also bare.

Abdomen

The abdomen is parallel-sided and features silver pollinose spots on a grey background. Tergite 5 is dark and unmarked.

Legs

The fore femur is pale on the apical third, while the mid and hind femora are pale at their apex. Both the fore and mid tibiae are pale on the basal third and at the extreme apex. The fore tibia has a row of strong, black, posterolateral setae. The lengths of these setae vary: in the basal third, they are approximately equal to the width of the tibia, and in the apical two-thirds, they are 2 to 3 times longer than the tibial width. Additionally, some apical setae reach the middle of the first tarsomere.^[2]

This species is currently known from two widely separated localities: a high-altitude (2200 m) meadow in the Altai Mountains, Russia,^[3] and High Creek Fen (3000 m) in South Park County, Colorado, USA, about 6,800 kilometres (4,200 mi) apart. This suggests that the Nearctic specimens collected in Colorado represent a separate, extremely morphologically similar species, or that P. alpigenus occurs in other high-altitude meadows and fens throughout the Holarctic Region.^[4]