nice caterpillar on fennel .

That's a jolly one - never seen that one before.
Had a little go at identifying it. The nearest was Foxmoth but that didn't have enough spots. Don't think its the one suggested on the Facebook page though.

I only know this one by the common name of " patch black swallowtail" butterfly. The "patch" refers to the white area on the top middle of the caterpillar which is thought to mimick a bird dropping.

Thanks for your efforts guys, Delonix will know if he sees the question. I guess I may have to ask if I remember how !

Daughter suggested it is a Black, Swallowtail Caterpillar, and others agree with this. I don't know what it ends up as yet. C'mon Delonix.

No doubt wildlifebalcony will be along with their pearls of wisdom soon.

You've got it Loosestrife, and it turns into a beautiful Butterfly.

Its a beauty Hank, I don't think I've ever seen one..
Must admit I had a chuckle at the comment, my words are often the same when getting in a pickle trying to add something....

Does anybody know if there are any other butterflies the same colour as their caterpillars? I couldn't think of any.

It's a Black swallowtailed butterfly (Papilio polyxenes).