I am about half way through my annual search for Purple Emperor larvae in / around Savernake Forest, Wilts. This is the 6th year I've done this. To date I have found only 12, and it looks as though this will be the poorest year I've recorded.
Part of the problem is the shortage of suitable mid-green, soft, matt foliage. Far too much of the foliage this season is thick and coarse leaved, which is dark-green or even blue-green in colour. This results from the early and rapid spring we had. It seems that late springs produce more suitable foliage for the late summer / autumn larvae.
I've found an unusually high number of failed breeding sites this season, where the larvae have vanished. This I attribute primarily to the preponderance of coarse, thick leaves, though the cold, wet August cannot have helped.
Another problem is extensive damage on previously favoured trees by frog hopper nymphs. They've trashed many of the best breeding trees, curse and crush them.
However, here's a healthy larva I found today, changing from 2nd to 3rd instar (a little on the late side) -