In what could be the biggest influx of butterflies into this country in decades, millions have flown into Britain from the deserts of north Africa. Up to 18,000 were spotted sailing on the breeze across Scolt Head Island on the north Norfolk coast: 50 arriving every minute according to Natural England nature reserve staff...As impressive as this migration is, it pales in comparison to the numbers of butterflies seen in past years:
This year, rumours of an impending invasion began circulating in late winter. A Spanish scientist, Constanti Stefanescu, reported seeing hundreds of thousands of them emerging in Morocco in mid-February after heavy winter rains in north Africa triggered the germination of food plants devoured by its caterpillars...
In Tudor times, Richard Turpyn recorded "an innumerable swarme of whit buttarflyes ... so thicke as flakes of snowe" that they blotted out views of Calais...There is a long article about the decline of British butterflies at The Guardian.
In 1892, SG Castle Russell took a walk through the New Forest: "Butterflies alarmed by my approach arose in immense numbers to take refuge in the trees above. They were so thick that I could hardly see ahead and indeed resembled a fall of brown leaves."