Snow cats in the Chilterns

Today saw the first reasonably heavy snowfall in our part of the Chilterns for quite a while, so we couldn’t resist heading up the hill for some sledging and to visit BBOWT’s Grangelands reserve. The air was crisp, and the snow-enveloped landscape was beautiful. I wasn’t really expecting to find much insect life to watch, so was surprised to see a small caterpillar crawling across the top of some fairly deep snow.

At first I thought this must be a one-off oddity, perhaps dropped onto the snow by a bird or carried there by the wind, but then I started seeing others. I found eight in a short space of time, all seemingly happy to be out and about on the surface of the pristine snow.

On closer examination at least some were caterpillars of the Large Yellow Underwing moth (Noctua pronuba), a well-known and very abundant species in the UK. I hadn’t been aware of its habit of being active in such conditions, but a web search leads to a number of American reports of similar snowy adventures for this species (see this post by Vermont naturalist Mary Holland for example, plus some additional photos on BugGuide). Large Yellow Underwing is an introduced species in America, and can be a pest species. Its winter activities are so well-known there that it also goes under the name of Winter Cutworm or Snow Cutworm.

I’ve always had a sneaking admiration for how well Large Yellow Underwing manages to survive in the modern world, but I’m even more impressed by its hardiness now! Has anyone else seen this snow-walking behaviour in the UK?

[Update at 15 December: thanks to Martin Townsend for pointing out that the brown caterpillar in the photo below looks like it is something other than Large Yellow Underwing, so it’s likely that at least two species were involved.]