Butterfly Conservation has been receiving reports since the start of the Bank Holiday weekend of sightings of large numbers of these butterflies.
People throughout Britain have seen these fast-flying butterflies moving overhead for hours on end, setting the scene for what could be one of the largest Painted Lady migrations in decades.
The first indication of their arrival in Britain came last Thursday (May 21) when Butterfly Conservation members first reported seeing large numbers off Portland Bill in Dorset. Since then, thousands have been seen flying north at locations across southern England, from Cornwall to East Anglia.
The fine Bank Holiday weekend weather brought hundreds of new sightings from as far north as Dumfries and Galloway in Scotland.
There were even sightings of hundreds in central London. An estimated 18,000 were spotted flying past Scolts Head Island on the Norfolk coast yesterday and were passing at 50 a minute over a 400m front today.
Scientists have been predicting an unusually large migration since late winter. The butterflies originate from the Atlas Mountains of Morocco, where heavy winter rains allowed good germination of the caterpillar food-plants.
A Spanish researcher, Constanti Stefanescu had reported seeing hundreds of thousands emerging in mid February and beginning their long flight north. They were seen in large numbers in Spain during April and a few weeks later in France.
Visit the migrantwatch survey pages to find out more about contributing to this nationwide survey.
Richard Fox, Surveys Manager at Butterfly Conservation, said: "There are literally millions of Painted Lady butterflies arriving right across Britain. This is a spectacular phenomenon".