As the leafmine season draws to a close (though I do still have a couple of finds to share early in 2022), I thought I’d post an update on our progress of monitoring the spread of the moth Stigmella aceris in the wider Cardiff area, a moth that was first recorded in Wales in 2019.

The map on the left below shows 1km squares where the moth’s larval leafmines were present as at 11 November 2020; the map on the right as at 29 November 2021. The red-coloured squares represent new finds during that year; the mustard-coloured squares are finds from previous years, i.e. in the left map, the mustard squares were finds made in 2019; in the map on the right, the mustard squares show the finds at the end of 2020. I am just one of several enthusiastic local members of Team leafmine who have been helping with this surveying, walking many miles to check each 1km square and, as the maps show, we have been able to confirm that Stigmella aceris has spread quite extensively in 2021.

The moth’s presence, of course, does depend on the presence of its larval food plants, the trees Field maple and Norway maple, so blank squares can indicate an absence of trees, rather than a failure to find any mines. Where the moth has been present for more than a year, it can be prolific, with several mines on each leaf of Field or Norway maple, whereas in newly colonised places, I’ve often found just one or two mines from a whole tree load of fallen leaves. It will be fascinating to check this tiny moth’s progress again in 2022.