Have you ever stopped to think about the effect of the wind on the butterfly numbers you see? For example, where did the 29 (we think!) Red Admirals in the photo above appear from? The total count on that ivy patch was actually 83, and there were also Painted Ladies and Clouded Yellows – all migrants to this country, though the Red Admiral is surviving our winters more often.
These butterflies mainly arrived here from continental Europe on northerly winds. Their arrival coincided with many records of rare moths in Dorset, some of them brought over the Atlantic by the remains of Hurricane Lee, which reached the UK on 20 September. The photo above was taken on 26 September.
So Red Admirals were moving northwards. But observations from Portland Bird Observatory suggest that this was followed by a very strong southward movement of Red Admirals returning to Europe for the winter. The Observatory news page for 8 October shows that the movement of the moths and butterflies coincides with a massive very high altitude southward migration of birds, whilst the next day Martin Cade says:
“… greater numbers of Red Admirals [than birds] on the move. Their inexorable southbound passage has been taking place on such a broad front across the island that it’s been impossible to enumerate save to say it must number in the many thousands – we’ve done a whole series of spot counts both in the Grove/Broadcroft area yesterday and at the Bill today that have varied from fewer than one a minute to more than six a minute; today we even took to scanning skyward (…it was very pleasant – verging on the soporific in fact – doing that up on top of West Cliffs) and regularly spotted single butterflies motoring past so high up that they couldn’t be resolved with the naked eye.”
There has also been a Monarch butterfly recorded on 12 and 14 October on the Portland Bird Observatory website. Almost certainly this (or these) arrived on the disturbed weather systems that have prevailed recently, either from the USA or possibly from the Canary Islands.