Xanthostigma xanthostigma

The most commonly reported snakefly in Norfolk.

The wing-venation is important for snakefly identification. This species is readily separated from the next commonest snakefly in Norfolk, Phaostigma notata, by the pale pterostigma and the position of the adjacent cell (cell 1) which starts and finishes more-or-less level with the start and end of the pterostigma. On Phaostigma (which has a darker pterostigma) and the less common Atlantoraphidia maculicollis cell 1 is offset from the pterostigma (towards the base of the wing) so the pterostigma starts much nearer the tip of the wing than the base of cell 1.

Separation from the much scarcer Subilla confinis is trickier. In Britain's Insects, Brock provides a forewing character that may be useful. On xanthostigma there is a vaguely mace- or cudgel-shaped cell running between the cell 1 and the opposite edge of the wing. On Subilla this equivalent cell at the edge of the wing is narrower and separated from cell 1 by another closed cell. The hindwing character given in Plant is probably safer but less likely to be visible on a photo of a live insect. The cell between vein MA and vein R is a different shape, more-or-less paralell in Subilla confinis with the two long sides opposite, and more kite-shaped in Xanthostigma with the two long sides adjacent (veins MC and R) and two short veins at the distal end.

This female was swept from Cow Parsley growing beneath Oaks on a breezy day. Note the right hindwing has abnormal venation.

female Xanthostigma xanthostigma showing left and right forewings, left and right hindwings, top and front of head and close-up of abnormal venation in right hindwing, Blackhall, North Elmham (Norfolk, UK), 22nd May 2023

Just four days later I caught another female at a different location, this one netted in flight. It was in damp alder carr woodland beneath a huge Wild Cherry (I think) and hazel and birch.

female Xanthostigma xanthostigma, Wendling Beck Environment Project (Norfolk, UK), 26th May 2023