Wildlife lovers are being urged to help record the greatest influx of painted lady butterflies for a decade as part of the world’s largest butterfly survey.

Unusually high numbers of the migratory butterfly have flown into Britain from continental Europe in the last six weeks and some of their offspring will emerge during the Big Butterfly Count, which starts on Friday.

This “painted lady summer” is the most significant since 2009, when 11m arrived in Britain. The butterfly is continuously migratory, with offspring making the reverse journey to warmer climes at summer’s end, with successive generations even crossing the Sahara before making their way north again next spring.

Chris Packham, vice-president of Butterfly Conservation, urged people to join in the survey in which people can download a free app and spend 15 minutes counting butterflies in their local park, nature reserve or garden.

“The painted lady migration is one of the wonders of the natural world,” said Packham. “Travelling up to 1km in the sky and at speeds of up to 30mph these seemingly fragile creatures migrate hundreds of miles to reach our shores each year.

“This butterfly undertakes an extraordinary 7,500-mile round trip from tropical Africa to the Arctic Circle every year – almost double the length of the famous migrations of the monarch butterfly in North America.

“Signs across Europe are looking very promising, meaning that 2019 could be a very good year for the painted lady with high numbers already being recorded across parts of the UK.”

According to Richard Fox of Butterfly Conservation, this year’s migration began with huge numbers of painted ladies in Cyprus, Rhodes and other parts of the eastern Mediterranean. Some of these insects’ offspring travelled through eastern Europe and into eastern England around 14 June. Others moved through Spain and arrived in western England two weeks later.

Fox said: “Lots of eggs have been laid so if the weather stays fair these should be emerging as adult painted ladies before the end of the Big Butterfly Count. That’s pretty exciting.”

The Big Butterfly Count is celebrating its 10th birthday this year and last year more than 100,000 people counted more than 1m butterflies during three weeks of high summer. Butterfly Conservation is working with Mind, the mental health charity, to raise awareness of the benefits of spending time in nature by doing things such as the count.

Packham added: “The mental health benefits of spending time outdoors watching nature have been blindingly obvious to me for as long as I can remember. Immersing yourself in nature, even if it’s just for a few short minutes, changes your perspective, it helps you slow down and notice what’s going on around you and it opens a door to the overlooked beauty and drama of our natural world.”