It is about two inches wingspan and the red underwing, which gives it its name, is only visible when it flies.
According to the ukmoths website that I consulted to identify it, it is very common in southern England and its caterpillars feed on alder and willow. It makes me wonder why this was a first for me!
We moor under willows and alders in southern England.
Etruria Junction Wed 23 Aug 2017
2 hours ago