I found this very battered Large yellow underwing when I went to add some compost the the bin. It looks as if it has been attacked by birds on more than one occasion.
I often find the fat caterpillars when I'm digging in the borders. I know they eat some of my plants, but I just leave them. It is worth it to get an occasional glimpse of the adult.
I had one in the greenhouse last year. It almost made me jump out of my skin, and I did drop my watering can. It was resting in the corner on the soil and some dead leaves. I bent over to pick up the leaves and it opened its wings to display the yellow. Well it certainly works, even on humans! I've seen the orange underwing too, but the startle reflex flashing works so well that I've not been able to catch one to photograph it.