Nearly half a million Painted Lady butterflies were counted in just three weeks this summer.

This natural phenomenon, which happens roughly once a decade, was noted during the 10th UK-wide Big Butterfly Count, an annual census run by the Lulworth-based Butterfly Conservation.

The 'Painted Lady Year' happens when unusually high numbers of migratory butterfly arrive in the UK.

Experts say it is too early to tell how 2019 compares to the last ‘Painted Lady Year’ in 2009, but the number seen in this year’s Big Butterfly Count was almost 30 times greater than in the 2018 survey, equating to an increase per Count of 2498 per cent on the year before.

Butterfly Conservation’s associate director of recording and research, Richard Fox, said: “The Painted Lady obviously stole the show this summer, taking the top spot in England, Wales, Scotland and Northern Ireland, but 2019 has also been the most successful Big Butterfly Count in its 10-year history, with more people taking part and more counts being submitted than ever before.”

Several other common species have experienced a bumper summer, helped by the fine weather.

The Peacock had its best summer since 2014, with counts up 235per cent on last year.

Meanwhile, the Marbled White experienced a 264 per cent increase and there was a 64 per cent rise in counts for the colourful red and black Six-spot Burnet moth.

Mr Fox said: "Last year the Small Tortoiseshell experienced its worst summer in the history of the Big Butterfly Count, so to see its numbers jump up by 167 per cent this year is a big relief. But what’s really interesting when we look at the results is how this species performed far better in Scotland and Northern Ireland this year - where it was the second most seen butterfly during thecount - but didn’t do nearly as well in England and Wales, where it only just made the top 10.

"On average, participants in Scotland and Northern Ireland saw over twice as many Small Tortoiseshells per count than people in England.

“We’re still trying to establish what is behind the long-term decline of the Small Tortoiseshell and while it is good news that the butterfly fared better this summer, the poor results in southern England in particular suggest that climate change may be having more of an impact on this species than we have previously realised.”

This year more than 113,500 people took part in the Big Butterfly Count, the largest survey of its kind in the world, spotting nearly 1.6 million butterflies in the UK during the three-week, high-summer recording period.