When this emailed photo arrived I assumed it was of a species of Tiger Swallowtail butterfly caterpillar from either Canada or the USA. The very similar Canadian Tiger Swallowtail, Eastern Tiger Swallowtail and Western Swallowtail are common butterflies in North America where their caterpillars are often found in gardens.
So I was more than surprised to discovered the photo was taken by Annemarie Scott in her garden in Northumberland!
I’m not knowledgeable about these species and I may have over looked some identification feature but it seems possible it’s an Eastern Swallowtail butterfly caterpillar which has been hatched from an egg imported into the UK on a plant. Excitingly, as this caterpillar has darkened in preparation to pupate, there is a real possibility that Annemarie will wake up one morning to a stunning Swallowtail butterfly in her garden.
Many thanks go to Annemarie for a fascinating enquiry.
Any suggestions as to this caterpillars identification or origin are welcome. Images of North American caterpillars and butterflies are always appreciated and will be added to the American gallery with accreditation.