The black and yellow banded Cinnabar moth (Callimorpha jacobaeae) caterpillars were feeding on Ragwort. It was generally agreed that it was good that Ragwort has some good uses - like feeding very hungry caterpillars - because it is not very good for horses if they eat it.
It is, as you can see, a very large caterpillar indeed. When he (or she) was first picked up he squirted some stuff at us, and then rolled into a ball and refused to come out again. We think the squirting must have been some sort of defense mechanism to deter predators. It certainly deterred some young bug-hunters!!