Posted on 22 October 2012
The butterfly migrates from the continent each summer to UK shores in varying numbers. But up until now scientists did not know if the Painted Lady made the return journey at the end of the summer, like the closely related Red Admiral, or simply died in the UK.
In one of the largest ‘citizen science’ projects ever conducted, scientists from the University of York and organisations including Butterfly Conservation, the NERC Centre for Ecology & Hydrology and Rothamsted Research, have discovered exactly what happens to Painted Ladies each autumn.
Rather than overwinter in one or two places like the Monarch butterfly, the Painted Lady just keeps going, breeding and moving, breeding and moving again
Professor Jane Hill
The Painted Lady does indeed migrate south each autumn - but makes this return journey at high altitude out of view of butterfly observers on the ground.
Radar records revealed that Painted Ladies fly at an average altitude of over 500 metres on their southbound trip and can clock up speeds of 30 mph by selecting favourable conditions.
The findings, published in the journal Ecography this week, also revealed that the species undertakes a phenomenal 9,000 mile round trip from tropical Africa to the Arctic Circle – almost double the length of the migrations undertaken by Monarch butterflies in North America.
The whole journey is not undertaken by individual butterflies but is a series of steps by up to six successive generations so Painted Ladies returning to Africa in the autumn are several generations removed from their ancestors who left Africa earlier in the year.
Study co-author, Professor Chris Thomas of York’s Department of Biology, said: "By heading northwards in spring conditions, the population shifts northwards in a series of generations. But those that develop in the long day lengths of northern summers head south again, achieving massive distances by riding favourable winds.”
Co-author Professor Jane Hill, also of York’s Department of Biology, added: "Rather than overwinter in one or two places like the Monarch butterfly, the Painted Lady just keeps going, breeding and moving, breeding and moving again, in a never-ending series of steps taking the whole population from Africa to northern Europe again, year after year."
More than 60,000 public sightings of the butterfly during 2009 were collected across Europe including radar images tracking butterfly movements across southern England with 10,000 British observers taking part.
Richard Fox, Surveys Manager at Butterfly Conservation, one of the report authors, said: “The extent of the annual journey undertaken by the Painted Lady butterfly is astonishing. This tiny creature weighing less than a gram with a brain the size of a pin head and no opportunity to learn from older, experienced individuals, undertakes an epic intercontinental migration in order to find plants for its caterpillars to eat.
“Once thought to be blindly led, at the mercy of the wind, into an evolutionary dead end in the lethal British winter, this amazing combination of mass-participation citizen science and cutting edge technology has shown Painted Ladies to be sophisticated travellers.
“We are extremely grateful to the many thousands of members of the public who reported Painted Lady sightings and contributed to this extraordinary discovery.”
Radar in Hampshire operated by Rothamsted Research revealed that around 11 million high-flying Painted Ladies entered the UK in spring 2009 with 26 million departing in autumn.