One of the longest standing mysteries of migration has finally been solved after scientists discovered where the UK’s Painted Lady butterfly population goes each autumn. The insect migration puzzle was answered partly thanks to one of the largest citizen science projects ever conducted.
The butterfly, a common immigrant, 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.
But in a major science project combining traditional monitoring by butterfly enthusiasts and new radar techniques, some 60,000 public sightings of the butterfly during 2009 were collected across Europe, with radar images tracking butterfly movements across southern England and 10,000 British observers taking part.
The findings have been analysed in a new science paper published this week in the journal Ecography by a team of international researchers, including UK researchers from Butterfly Conservation, the NERC Centre for Ecology & Hydrology (CEH), Rothamsted Research and the University of York.
The scientists discovered that the Painted Lady did indeed migrate south each autumn but made 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 30mph by selecting favourable conditions.
The findings 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 famous 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.
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.
Richard Fox, Surveys Manager at Butterfly Conservation, was one of the paper authors. He 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.
"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.”
The paper reference is Stefanescu et al (2012), Multi-generational long-distance migration of insects: studying the painted lady butterfly in the Western Palaearctic. Ecography. doi: 10.1111/j.1600-0587.2012.07738.x
Butterfly Conservation issued a press release for this story