Maple Dot Stigmella aceris

The old vernacular name, Scarce Maple Pigmy, was appropriate once, but since 2018 this species has become very common so "Scarce" is no longer an accurate reflection of the species' status.

This was my first adult. As the specimen was quite fresh I first attempted to key it using the Nepticulidae key at www.kleinevlinders.nl. Using this it keyed pretty directly to Stigmella aceris. The very last couplet (a choice between aceris and Stigmella crataegella) was slightly ambiguous perhaps, as although the area of the forewings basal to the fascia were dark golden brown with a purplish tinge, this purple tinge didn't seem to be particularly concentrated along the costa. The purple was much clearer in the distal part of the wings. The antennae were short so aceris seemed the most likely ID, but I was keen to eliminate crataegella carefully when examining the genitalia.

Female Nepticulid genitalia are always delicate and despite taking what I thought was an abundance of care, the corpus bursa did not come out cleanly. I was left with the bulged base but the rest was reduced to a thin rag. I think I could see enough to confirm the ID though. The apodomes are, I think, too long and curved for crataegella but match aceris, and there are sclerotised areas around their bases that seem to be a feature of aceris. Also the way the base of the corpus bursa (or I guess it's the ductus bursa here?) bulges out to one side seems to be characteristic of aceris and although there wasn't as much texture on this bulge as shown in some photos, there was clear sign of striations in the area immediately below this which is evident in photos and diagrams of aceris genitalia (these sriations are not clear in my photos but were easily visible through the microscope).

female Maple Dot Stigmella aceris showing genitalia, Wendling Beck Environment Project (Norfolk, UK), 11th September 2023

My first experience of the leaf-mines was when some were pointed out to me on a Norfolk Moth Survey event at Lynford. I didn't record what they were on but from what I can see of the leaves they look like maple of one or other species.

Maple Dot Stigmella aceris leaf-mines, Lynford (Norfolk, UK), 13th October 2018

I noticed several on Field Maple when I photographed this one. The frass was noticeably green and dispersed across most of the width of the gallery in a crescentic wave-like pattern.

Maple Dot Stigmella aceris leaf-mines, Elmham Park, North Elmham (Norfolk, UK), 16th September 2022