The larvae of this small plume moth feed within Hemp Agrimony stems.
They make a hole, presumably to allow removal of frass, and to allow the moth to escape.
The holes occur at or just below a swollen node/gall, as in the photo.
The larvae overwinter in the stem, eventually pupating in the same place.
To rear keep the stems outside, only bringing them inside close to their emergence time in spring. This one was found 20th Jan this year.
UK Moths - details