According to the web link below, of the UK Butterflies web site, the only occasion the Southern Festoon (Zerynthia polyxena) butterfly has appeared in Britain was in May 1884. Fortunately a few days ago, I found the actual original newspaper report which I reproduce.
This url http://www.ukbutterflies.co.uk/species.php?species=polyxena gives the statement immediately below.
“A single specimen was caught by two boys on 27th May 1884 near Exeter, Devon, and it is believed that is was originally purchased as a pupa from a natural history dealer.”
The newspaper report, from The Exeter and Plymouth Gazette Daily Telegram May 31st 1884.Annotated by myself.
A STRANGE BUTTERFLY
To The Editor of The Exeter and Plymouth Gazette
I had yesterday brought to me a very good specimen of the beautiful Thais polyxena(1), a European butterfly. It was captured in the immediate neighbourhood of the city (2) by two boys.The insect had by all appearance but just emerged from the pupa state , as its hind wings had not quite expanded to their full development. It was scarcely dead when I received it. What I should like to know is this – Has any lady or gentleman brought over from the Continent any larvæ or pupæ of foreign butterflies? This is one that had escaped ,perhaps, in the larvæ state. The insect is so unlike any of our British species that it is sure to attract attention, and it would be interesting to know how it got introduced. (3) (4)
According to Wikipedia the current distribution of the Southern Festoon is south-eastern France,Italy,Slovakia and Greece,covering all of the Balkans and reaching the south Kazakhstan and the Urals.
According to an archive weather chart of May 30th 1884 wind direction was from the east over Devon and not the south-east,which is where it should have been from to blow this butterfly in from France. This link should take you to a page which has a drop down menu on the left hand side (in German). You can put in the dates May 29 1884 and so on. The wind direction on May 29 was about ENE, 30 E
1. The name in 1884 for the Southern Festoon
4. The Exeter and Plymouth Gazette 31-5-1884