Mullein Moth Caterpillar (Cucullia verbasci)
The verbascum family of flowers tend to grow in waste places and scrubby areas, often where their is open ground and little competition from more aggressive species. Not surprising then, that is where you find this moth.
The adult flies in April and May and I have never seen it despite being a common moth. The reason it is fairly seen is that it is one of the few species that does not seem attracted to light and therefore a moth trap is of little interest to them.
The caterpillars emerge in late June and are just about at the end of their time now; they will shortly pupate and over winter in this state ready to emerge in the spring. However, they can stay a pupa for up to four years before emerging which is quite remarkable.