And wonder you should when you stumble upon such interesting creatures. I am pleased that you have wandered with your wonder to just the right place.
This is a wingless moth, a female in fact, and she just sits around when emerged from her pupa waiting for the attentions of a male, hence the lack of wings - they are just not required for her sedentary lifestyle. Perhaps that's a little unfair to suggest she is completely lazy as she does her best to make herself alluring to passing males with wafts of pheromones that can attract many males and from quite a distance - the guys have wings. At this stage her abdomen is full of eggs, but not yet fertile. There are several species that emerge at this time of year but this looks to be the Mottled Umber, Erannis defoliaria.