While looking for the Toadflax Brocade larvae last Sunday I also spent a bit of time searching for larval cases of Coleophora artemisicolella on Mugwort. I was looking for the holes the larvae make in the seed heads (see photo on ukmoths) but couldn't find any of these. I did see a couple of suspicious looking seed heads which were browner than the others and attached to other seed heads at odd angles. I thought these might be the larval cases themselves so I took them home for closer inspection. By the next day frass had appeared in the container and one of the seed heads had moved, confirming it was indeed a larval case. Some of the feeding holes have since appeared too.
Coleophora artemisicolella larval case (top right)
Coleophora artemisicolella larval case (centre)
As far as I know there are just two previous South Wales records of this species, both from Carmarthenshire in 2005. Doubtless it is under-recorded as the cases are hard to spot - I just got lucky with the first one, which was sticking out at 90 degrees to the other seed heads on the plant. Worth looking for if you have any good stands of Mugwort locally.