Plenty of these seen on sea defence boulders but no idea what they are. About 10mm in length, hope someone can ID it, thanks.
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Caterpillar of a Marbled Beauty moth
According to UK moths http://ukmoths.org.uk/show.php?bf=2293
The caterpillars feed on lichens on rocks, which explains what they were doing on the boulders where you found them.
University of Edinburgh and Biodiversity Observatory (OU)
Lat/Lng: 50.1472, -5.0557
OS grid ref: SW817319