I discovered this caterpillar yesterday feeding from a silken retreat on my Water Mint. It is the Mint Moth (Pyrausta aurata), of which I have seen the small adult fluttering around on several occasions.
The larvae feed on all kind of Mint, but this one has taken quite a chance, for the Water Mint is growing in my garden pond, and this caterpillar has found itself on one tall spike in the centre of it. Good job it is well anchored by its silken threads. Believe it or not, but some caterpillars can swim, but not all can.
Rear garden pond, Staffordshire, England. July 2017.