Message and a picture from Ian Bushell.
Here’s a bit of fun. While we were clearing diseased Ash out of the copse by the picnic area, I noticed these slugs on some of the trees. I was quite amazed because some were way up towards the top of the trees we were cutting down – at least six or seven metres. This one in the header photograph was on his/her way down the tree trunk.
Tree slug, Lehmannia marginata © 2021 BBC.
When I got home, I dug around in some reference books and on Google, and I believe they are Lehmannia marginata, also known as Tree Slugs. They are apparently quite common and, as in this case, abundant on trees in woodland and hedgerows.
They feed on lichens and mosses growing on the trunk and branches of trees, which makes them a good indicator of air quality. Because of their diet, they are not a threat to your garden plants so if you find them in your ornamental shrubs and trees, don’t worry, they are not damaging your trees.