Cinnabar Moth - parasitic wasp?

[millerd]

At Chobham Common today, Cinnabar moth caterpillars were busy eating their way through every ragwort in sight. However, on one flowerhead, these normally placid creatures were thoroughly agitated by the presence of a large black wasp - to the extent that my picture does not freeze the action and the caterpillars are blurred.

Does anyone know if there are any frequent parasites on these caterpillars, and is this one of them?

Dave