Now you see me, now you don't

I was walking home through the University woodland area in the afternoon when a large flying insect called my attention, a moth with bright pink hindwings and an erratic flight. It took a while to settle, and it did so on a tree trunk. When I got close I could not see it. I had spotted it when it had landed, so I took a few shots of the trunk, where was it? Can you see it?

and then I saw it. Thanks to it hindwings being slightly exposed.

It was a Red Underwing (Catocala nupta), a large noctuid which flies in August and September, and whose caterpillars feed on poplar and willow. It seems to be a rare species in the North, but it seems to be expanding in range. In the  NBN gateway it does not even appear in Hull.