Hi Suzanne,
Judging from the amount of (pro)legs or whatever they're supposed to be called it's not a 'caterpillar' but a sawfly larva, so you'll probably need to looking at different references
You'll find some (old?!) links to non-lepidoptera 'caterpillars' under the header "Andere rupsen"
here.
A size estimate could probably also be helpful
Cheers, Arp