Endothenia nigricostana
Wingspan about 13mm. The adults are quite distinctive, typically with a yellow or ochreous blotch on the dorsum, although this can be less obvious on darker examples.

It inhabits woodland margins and embankments.
The adults fly in June and are active in late afternoon as well as after dark.
The larvae feed on Marsh Woundwort (Stachys palustris), eating down from the flower into the stem and roots.
This species is distributed thinly but fairly widely across the southern half of England and Wales, ranging more scarcely northwards to northern England. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified local.
It appears to be uncommon in Leicestershire and Rutland, where there are few records. L&R Moth Group status = D (rare or rarely recorded).
Leicestershire & Rutland Map
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MAP KEY:
Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015