This late in the year, there are few butterflies about but there is always a speckled wood (Pararge aegeriais) somewhere. Here is one on hawthorn berries photographed in September 2019 by DKG.
As its name implies, it is a woodland species; its habitat of choice is the dappled sunlight at the edge of a deciduous wood. It feeds mainly on aphid honeydew in the tree tops but when there are fewer aphids, in the autumn or early in the spring, it will feed on nectar.
Left: adult feeding on nectar by Ian Bushell; right: late instar caterpillar (CC)
The caterpillars are bright green and they feed on several species of grass. They pupate after about ten days, the chrysalises suspended beneath grass blades.
Uniquely among British butterflies, speckled woods are able to hibernate as either a caterpillar or a chrysalis. This means that there is an unbroken progression of adult butterflies from early spring; first the over-wintering pupae hatch, then the over-wintering caterpillars pupate and hatch. These spring-time adults mate and produce the summer’s brood, which are the adult butterflies that will later produce the generation that hibernate as either caterpillars or pupae.
Header and footer pictures by DKG
Southwick Country Park Nature Reserve 
That’s fascinating, I never knew they had such an interesting life cycle.
I find the butterflies that overwinter as adults the most interesting. They all seem to have the most extraordinary camouflage techniques.
During the winter I stand my wheelbarrow up against a fence and will usually find a peacock butterfly overwintering inside it!
And if you disturb it, it will flash its wings open to show its eyespots so that it looks like you (if you were a mouse) just woke a big bird of prey.