This might not look like much but I’ve been looking for one of these for perhaps a year, at least during the months when it was around to be found. And if I hadn’t been looking closely at the leaves of this Wych elm, I could so easily have missed it. These are the leafmine and the case of Coleophora badiipennella, the Pale Elm Case-bearer (click on the link here to see the adult moth on the UK Moths website).
According to the British Leafminers website, the larva:
initially forms a gallery along the midrib, which then goes out along a vein (see photo). The end of this gallery is then excised to construct the first case. It then feeds close to this and makes several small mines …
If you look at my photo above, you can see where the larva has made a second mine below the first – you can see the tiny hole where it would have attached itself – before moving to the third mine where it was then feeding. I haven’t been able to find much information about pupation but I presume the larva remains in its case, falls to the ground either still attached to its leaf when the leaf falls or after detaching itself, and over-winters on the ground. It seems many of these leafminers are not very well studied … yet.