My sharp-eyed youngest son spotted this colourful caterpillar in the corkscrew willow tree. It is the caterpillar of the Grey Dagger moth (Acronicta psi, #611). I’ve caught adults in the moth trap, which are virtually indistinguishable from the rarer Dark Dagger moth, but the caterpillars of the two species are quite different. Grey Dagger caterpillars are found on a variety of deciduous trees, such as Oak, Birch, Hawthorn, Elm and seemingly Willow too.