This is a swallowtail caterpillar, Papilio machaon.
Yes, it is about to pupate - the silk girdle is visible.
But... in North Somerset!
That is way outside the normal distribution of the British race (parts of the Norfolk Broads).
Migrants of the continental race have been recorded at many localities in the south of the UK
But it is much rarer for larvae to be spotted...
Do you have any of its foodplants growing nearby?
- Milk-parsley (Peucedanum palustre) - used by the native race
- various umbellifers such as Wild Carrot (Daucus carota) and Wild Angelica (Angelica sylvestris) - used by the continental race
Do you know anybody who rears butterflies locally? (maybe it escaped)
I suggest you tell Peter Eels about this (email@example.com), he runs the website above.
And report it to Butterfly Conservation (http://butterfly-conservation.org/55/contact.html)
Good observation Richard!
Thanks - I thought I was seeing things! I went back and forth through Porter knowing what it looked like and convinced it must be something else. Checking the Millenium Atlas and Butterflies of the Bristol region just made me more suspicious. If an adult had been spotted in the village then I'm sure we would have heard.
Caterpillar is still there this morning and still in the same state. It is on the edge of a patch fennel 6ft tall, which is the closest we've got to anything approaching its normal food plants in this garden.
Will follow up the links you sent.
Thanks for the update; good; keep us posted!
How exciting - yes please keep us updated.
Richard, you are SO lucky! I knew someone who lived on the south coast who saw an adult swallowtail flying in their garden. He assumed it was an escape from a butterfly farm. But there are usually several sightings a year (in the south UK ) of Swallowtails that have flown in from the continent. For you to have a larva about to pupate could point to the fact that continental Swallowtails have come over and bred in your garden. Wouldn't it be lovely if Swallowtails established in southern England?
Thanks for the repsonses. On Bank Holiday Monday morning the larva was still looking very much like a caterpillar. When I got in from work in the evening it had become a pupa, as per the photograph. The general consensus seems to be that it is either the result of an escapee from captive breeding or offspring of one of the European race (gorganus) that have been spotted along the souh coast this summer. Either way it was a bit of a shock!
Now, if it is either captive breed or European race, will it be robust enough to survive our winters? Any thoughts on whether I should/am able to do anything to increase its chances of survival?
Turning into a nice story.
I'd be guided by what BC have to say.
So, the weather has been warm and the swallowtail hatched today, almost exactly 5 weeks after pupating. As you can see one tail was missing, but otherwise it was fine. It spent an hour on the patio warming itself up, not fazed by the visits of neighbours annd then flew high and strong over the trees and is currently visiting local gardens. However, today we were also visited by a party of ten blue tits plus a few great and coal tits and there are plenty of other hunrgy birds about... and the temperatures at night aren't so rosy.
Thankyou so much for this update. I have been wondering what happened. You are so lucky and at least now you can prepare yourself for next year and keep a close eye on that fennel plant of yours and its potential rare and beautiful visitors :-)
Thanks for letting us all in on this story!