Sunny September brings butterfly invasion

Britain's sunny September has brought about an autumn invasion of butterflies, with thousands of red admirals, clouded yellows and large whites migrating into southern England from across the channel.

The movement has come at the end of a summer which saw the biggest migration of butterflies into the UK for more than decade, with tens of millions of painted ladies pouring into Britain from their breeding grounds in North Africa. At one stage it was estimated there were a billion painted ladies in Britain.

Butterfly migration from Europe has usually long ceased by now, but over recent days there have been numerous reports of newly-arrived insects along the south coast. Clouded yellows in particular have been observed in substantial numbers, with counts of up to 600 at coastal localities in Sussex; they have also been seen in Cornwall, Devon, Dorset, Hampshire, Kent and on the Isle of Wight.

"The fact that these butterflies are clustered so close to the coast points to the fact they are new arrivals," said Dr Tom Brereton, Head of Monitoring with the charity Butterfly Conservation. "There have also been sightings at sea, where unusually, the butterflies have been travelling north towards England, rather than south towards wintering areas."

There is also evidence that painted lady butterflies are continuing to arrive from mainland Europe, again well after migration into the UK has normally ceased.

In May this year, there was a massive painted lady immigration, following ideal breeding conditions last winter in North Africa's Atlas Mountains. It was the first year that a large-scale migration had been monitored all the way from Morocco, and there is now considerable interest in the reverse journey, as there has long been speculation that they migrate back to North Africa, although there is no solid evidence, Painted ladies and clouded yellows butterflies cannot normally survive the UK winter.

Dr Brereton said: "We are appealing to anybody who sees Painted Ladies apparently heading out across the Channel or heading south across France to go to www.butterfly-conservation.org where they can log their sighting."

The Indian summer has also helped resident butterflies to fly well into the autumn, with 20 species (a third of all UK species) still on the wing. This includes very rare second broods of white admiral and third broods of brown argus.

Dr Martin Warren, Chief Executive of Butterfly Conservation, said: "It was fantastic to see so many painted ladies and now to have all these clouded yellows. However, we have to remember that these are not native butterflies. Their appearance is the result of a rare combination of circumstances, mainly in North Africa. Most British butterflies continue to decline. Until we halt that decline the vast majority of summers will see very few butterflies in many parts of the country."