Painted Lady Butterfly - Vanessa cardui

The garden is still alive with butterflies, mainly Small Tortoiseshell, I have seen a single Peacock and a single Red Admiral.  Then late this afternoon we spotted this fine "Lady".  Actually I am not sure if it is possible to tell male and female apart I certainly can't.

Painted Lady Butterflies are a species which migrates.  Every year they spread out from North Africa, and the middle East recolonising Europe and reaching the British Isles.  The  numbers vary each year, it is said this is a good year but I have only seen the one so far.

They have been seen as far north in the British Isles as the Shetlands.  Since the 70s the sightings have gone up by 32%.  Bearing in mind these butterflies originate on the desert fringes of N Africa it can't possibly have anything to do with global warming.   Can it?