Don Reynolds of the Natural Resources Institute (NRI) was part of a large international team, led by the Spanish ecologist Constanti Stefanescu, which was assembled to map the whole migration circuit of the Painted Lady butterfly in the Western Palaearctic Region.
The Painted Lady is a common immigrant to the UK, but scientists were never sure if it made the return journey at the end of the summer. This study has revealed exactly what happens to these butterflies when the seasons change.
Results from tens of thousands of public sightings showed that, during seasonal movements over six successive generations, the species may cover a 13,000 km round trip from West Africa to Scandinavia and back. As well as the huge 'citizen science' element, the study utilised several types of radar, which can detect butterfly-type targets flying high above the visual range of earthbound observers.
Don and collaborator Jason Chapman, using an insect-monitoring radar in Hampshire, shed light on the outstanding Painted Lady mystery – why the 'return' migration of the late-summer generation is so inconspicuous compared to the easily-visible spring invasions of northern Europe.
The radar indicated that southward movements of many Painted Ladies occur on strong winds at altitudes of several hundred metres. Don Reynolds, commenting on the radar findings, said: "wind-assisted migration at altitude would be particularly advantageous in view of the extremely long distances, between the European continent and West Africa, to be covered by this generation of butterflies."
The interpretation of the ecology of this butterfly may aid understanding of migratory strategies in other insect migrants, some of which could become serious invasive pests of northern Europe in the future.
Photo credit: Jane Hill