Grey Birch Dot Stigmella lapponica

Like other members of this family, primarily recorded in its leaf-mine stage. It is reasonably well-recorded across Norfolk but adults are rarely identified. Formerly given the vernacular name Drab Birch Pigmy.

This one was netted in flight and immediately looked interesting. The coarse dark scales beyond the pale fascia and especially the rather pale brown colour of the forewing struck me as different. My initial research led me to believe it was probably either Stigmella lapponica or Stigmella confusella. I favoured the former but there seems to be a fair bit of variation with both species and it clearly needed to be dissected to make sure.

An initial look at the genitalia quickly confirmed that it was indeed one of these two species - the oversize central horn of the gnathos is distinctive. Comparing the images on the Dissection Group website I could see reasons to favour lapponica but it wasn't clear-cut. The Kleine Vlinders key for external characters was supportive and a look at the genitalia diagrams at the Svenska fjärilar website also left me leaning towards lapponica. But as is often the case with such things, none of the references actually state what the important differences are, and when you think you find a difference after studying the images, you only go and find an image that seems to contradict what you thought. One last place to look was Chris Lewis's excellent British Lepidoptera site. He hasn't covered either species yet, so it didn't look like this was going to help - until I noticed a link to a key. I'd not seen this page before but it's extremely helpful! This enabled me to be confident that it was indeed lapponica based on the strong difference between the sizes of cornuti (which I'd thought was probably a significant difference) and the width of the notch in the uncus.

male Grey Birch Dot Stigmella lapponica showing genitalia (at various selective focuses and positions), Foxley Wood (Norfolk, UK), 21st April 2023