I was searching oak branches at the nature reserve for galls - having been thoroughly bitten by that 'bug' now - when I came across this nest of Buff-tip Moth caterpillars. They stay in groups like this and will strip the whole branch of leaves before moving on to another. When fully fed they become solitary and descend to the ground to pupate in the soil.
When I first saw them, with their protective fine hairs and ladder-like markings, a had a brief heart-stopping moment when I thought the dreaded Oak Processionary Moth might have reached the reserve from the areas in West London and Berkshire where it is starting to become a nightmare problem. Anyway, all is well - this one should only strip a few branches, not the whole wood.