Monarch butterflies are famous for their epic migrations across North America. But scientists have discovered that another butterfly travels even farther. Painted lady butterflies complete a multigenerational migration of up to 9,000 miles (15,000 km), making it the longest known butterfly migration on Earth.
No single butterfly completes the entire journey. Instead, successive generations continue the migration, with each generation flying part of the route before reproducing.
Painted lady butterflies (Vanessa cardui) are one of the world’s most widespread butterfly species, found on every continent except Antarctica and South America. Their remarkable distribution is due to their adaptability, allowing them to thrive in habitats ranging from meadows and gardens to forests and arid deserts.
Unlike monarch butterflies, which migrate between North and Central America, painted lady butterflies undertake the longest known migration of any butterfly species. As temperatures cool in autumn, populations move toward warmer regions where conditions are more favorable.
Painted Lady Butterflies Migrate in the Fall
Each fall, large populations of painted lady butterflies (Vanessa cardui) migrate from Europe to subtropical Africa. Their journey takes them across the Mediterranean Sea, over the mountains of North Africa, and across the Sahara Desert, with some individuals traveling up to 2,500 miles (4,000 kilometers).
While impressive on its own, this southward journey is only half of an extraordinary migration cycle.
Over the course of several generations, painted lady butterflies complete the longest known migration of any butterfly species.
Where painted lady butterflies overwinter
Although scientists had long known that painted lady butterflies spent the winter somewhere in Africa, the exact breeding grounds remained a mystery until recently. Previously, ecological niche modeling (ENM) had predicted potential winter breeding grounds in the humid regions near the tropics from November to February.
Led by Gerard Talavera, an entomologist and evolutionary biologist with the Botanical Institute of Barcelona, researchers used fieldwork to not only confirm the ecological niche model predictions but also locate new breeding sites, document the butterflies’ year-round life cycle, and identify the plants they use for laying eggs.
After two years of fieldwork scanning sites in sub-Saharan Africa, researchers discovered that after spending most of September to November in semiarid savannas, the butterflies follow the wetter weather further south to Central Africa’s savannas and highlands.
Preferred host plants for painted lady butterflies in the Afrotropics
These semi-humid regions provide ideal breeding habitat. Painted lady butterflies produce several generations in sub-Saharan Africa before successive generations continue the northward migration beginning in late winter.
During field surveys in the Afrotropics, researchers identified larval host plants for the painted lady butterfly from 12 genera across three plant families: Asteraceae, Fabaceae, and Malvaceae. However, in Western Africa, only two host plant species were found: Zornia glochidiata (Fabaceae) and Pseudoconyza viscosa (Asteraceae). These plants were abundant in typical habitats for the butterfly and were heavily used, with many caterpillars on each plant, suggesting they are the preferred hosts in this region.
The study highlighted the importance of the Afrotropical region and filled a major gap in scientists’ understanding of the longest known butterfly migration.
Studying How Painted Lady Butterflies Migrate from Africa to Europe
As Central Africa enters the dry season, successive generations of painted lady butterflies begin the return journey to Europe. While scientists had long suspected this northward migration, direct evidence proving where the butterflies originated had remained elusive.
A study published in 2018 by researchers from the University of Ottawa and the Institut Botà nic de Barcelona provided the first direct evidence that painted lady butterflies migrate from sub-Saharan Africa back to Southern Europe each spring. Rather than tracking individual butterflies, the researchers analyzed naturally occurring hydrogen isotopes preserved in the butterflies’ wings.
The ratio of hydrogen isotopes varies geographically because rainfall in different regions has distinct chemical signatures. Since butterfly wings form during the caterpillar stage and do not change afterward, the isotope composition of an adult butterfly’s wings reflects where it developed.
Researchers analyzed butterflies collected in Europe between February and April and compared their isotope signatures with those from different regions of Africa. The results showed that many of the butterflies had developed in sub-Saharan Africa before making the long journey north across the Sahara Desert and the Mediterranean Sea.
The study provided the first direct evidence of the painted lady’s annual return migration, confirming that the species completes a remarkable multigenerational migration cycle between Europe and Africa.
How African vegetation influences spring migration
A separate study found that the abundance of winter vegetation in the savannas of sub-Saharan Africa is the primary factor influencing how many painted lady butterflies migrate back to Europe each spring.
Because painted lady butterflies breed year-round, favorable winter growing conditions allow populations to increase rapidly. In years when vegetation is especially abundant, the number of butterflies making the northward migration can be up to 100 times greater than in years with poor plant growth (Hu et al., 2021).
Together, these studies reveal how climate, vegetation, and the availability of host plants drive one of nature’s most remarkable insect migrations. Spanning two continents and completed over multiple generations, the painted lady’s annual journey is the longest known migration of any butterfly species.
References
Garcia de Jesús, E. (2023, April 11). The last leg of the longest butterfly migration has now been identified. Science News. https://www.sciencenews.org/article/painted-lady-butterfly-migration-identified
Hu, G., Stefanescu, C., Oliver, T. H., Roy, D. B., Brereton, T., Van Swaay, C., … & Chapman, J. W. (2021). Environmental drivers of annual population fluctuations in a trans-Saharan insect migrant. Proceedings of the National Academy of Sciences, 118(26), e2102762118. https://doi.org/10.1073/pnas.2102762118
Talavera, G., Bataille, C., Benyamini, D., Gascoigne-Pees, M., & Vila, R. (2018). Round-trip across the Sahara: Afrotropical Painted Lady butterflies recolonize the Mediterranean in early spring. Biology letters, 14(6), 20180274.
Talavera, G., GarcÃa-Berro, A., Talla, V. N., Ng’iru, I., Bahleman, F., Kébé, K., … & Vila, R. (2023). The Afrotropical breeding grounds of the Palearctic-African migratory painted lady butterflies (Vanessa cardui). Proceedings of the National Academy of Sciences, 120(16), e2218280120. https://doi.org/10.1073/pnas.2218280120
This article was first published on June 22, 2018 and has since been updated
