11 September 2023
On the trail of the painted lady butterfly
Published online 12 April 2023
Field research resolves long-standing question of where painted lady butterflies spend the European winter.
The painted lady butterfly (Vanessa cardui) is renowned for its long migration path, travelling thousands of kilometres between Europe and Africa. While the migration cycle is well understood for Europe and North Africa during the spring-to-autumn period, knowledge of where the butterflies spend winter has remained limited.
Now, based on ecological niche modelling and assessment of the resulting predictions through field surveys, an international team of researchers, including Mohammad Marafi in Kuwait, has documented extensive winter breeding in the Afrotropical region south of the Sahara Desert. Their findings expand the multigenerational migratory cycle by up to 15,000 kilometres.
The team conducted seven field expeditions across the Afrotropics during the months of December and January between 2017 to 2020 to test the reliability of previously predicted breeding probability maps. The expeditions spanned a wide longitudinal range from West to East Africa: Cote d’Ivoire, Ghana, Benin, Cameroon, Uganda and Kenya.
In addition, monitoring data were collected between September 2018 and June 2020 across nine sites in the Canary Islands, Senegal, Benin, Cameroon, Ethiopia and Kenya. The team visited sites that had abundant larval host plants as well as hilltops near the breeding sites to track adult activity. They documented 2,755 caterpillars in the breeding sites and 1,198 adults at hilltops.
Overall, the field observations validated the model-based predictions, indicating that the niche modelling technique may be generally useful to predict the distribution of other migrating insects. Such predictions are important for conservation, pest management and ecosystem monitoring related to climate change.
“We show that painted ladies rely on both the Palearctic and the Afrotropics to complete their annual cycle. Having such a wide ecological niche is quite an exceptional adaptation in butterflies,” says Gerard Talavera at Consejo Superior de Investigaciones Científicas (CSIC), in Spain, who leads the Worldwide Painted Lady Migration Project. “While the Sahel and northern Savanna are suitable for reproduction from September to early November, these regions become dry and unsuitable later on, so butterfly populations reproduce further south from December to February.”
The study identified host plants used by painted ladies such as Zornia glochidiata in West Africa, Echinops giganteus in Central Africa and Carduus keniensis in East Africa.
“Perhaps not since monarch overwintering colonies were documented in the scientific literature have we understood so clearly the full annual cycle for another long-distance insect migrant,” says Dara Satterfield, an ecologist at the Smithsonian National Zoological Park, US who was not involved in the study.
“I am struck by how the study puts the whole story together, how these beautifully spotted butterflies traverse the world over 10 generations and 15,000 kilometres. Down to the host plants that the butterflies use, the researchers reveal what happens after painted ladies breed in Europe during the summer and then cross the Sahara as temperatures drop.”
Noting that the study involved input by researchers from 12 countries, Satterfield says: “This is the scale of international collaboration that we need to solve the many remaining mysteries of long-distance animal migration. We often only have a piece of the story for any migratory animal. This collaboration closes the migratory circuit, so to speak, for painted lady butterflies.”
Talavera, G. et al. The Afrotropical breeding grounds of the Palearctic-African migratory painted lady butterflies (Vanessa cardui). PNAS https://doi.org/10.1073/pnas.2218280120 (2023).