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 (in that example it is also separated from cell 1 by another closed cell but this does not appear to be the case always). 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 Project (Norfolk, UK), 26th May 2023

This one was swept from gound-level vegetation under trees at the edge of a woodland on a windy day. I was sweeping under a pine tree in the hope of finding Atlantoraphidia maculicollis - that wasn't to be this time, but any snakefly is always nice. This one was missing its forewing on its left side.

female Xanthostigma xanthostigma, Wendling Beck Project (Norfolk, UK), 11th May 2025

This my first male was swept from birch underneath Pedunculate Oak on a breezy day. I was keen to examine the sculpturing of the head having recently learned that there is a further difference between this species and Subilla confinis, namely that this species has a smooth head vs. coarsely sculptured on Subilla confinis. I am yet to see a sufficiently close-up and sharp photo of Subillus (or a specimen) to really understand how coarse it is on that species, but the dorsal surface of the head certainly is shiny and smooth on Xanthostigma. Not, however, uniformly so, so this could be misinterpreted perhaps - Xanthostigma is covered in obvious punctures, but these are well spaced and the surface between the punctures is very smooth and shining. On this specimen at least, there is also a broad dull strip along the midline along the rear half of the head.

In a British context at least, I don't think one would normally need to resort to examining the genitalia for identification, but as I had the specimen I thought it might be worth documenting this just in case it is helpful at some point.

Note that on one or two of the photos of the live insect below there are red reflections that come off the casing of the Olympus TG7.

male Xanthostigma xanthostigma, Hoe Common (Norfolk, UK), 18th May 2026