Feverfew - what they are is annoying (sorry!).

Google images of Light Knotgrass Moth ... possibly that?

How about Vapourer Moth? Or Gypsy Moth?
Be careful of the hairy ones when moving though

Unless you are very sure what they are and what, if anything else, they will eat, they are unlikely to survive if you move them. I would feel inclined to let them munch on as the heuchera will probably survive as there are only 3 caterpillars. Or maybe the heuchera could be split and you could let them have one piece? I say this because the caterpillars do look interesting and might be larvae of something that is endangered. Who knows! Anyway you can tell I'm a bit obsessed with wildlife and conservation!

Thank you for your replies, I know it's not the clearest of photos taken with IPad. I don't think it is the Vapourer, but it certainly resembles both the Knot grass caterpillar & the Gypsy moth also. Anyway I'm going to leave them alone, soon they will pupate & I hope there will not be too many next year. Will take a chance on it!

Glad you are giving them a chance and hope they turn out to be something interesting!

Good thinking Feverfew:)