Butterflies traverse vast Sahara desert in longest known insect migration
Weather conditions have a great influence on the number of migrations.
A species of butterfly found in sub-Saharan Africa is able to migrate thousands of kilometers to Europe, crossing the Saharan desert in years with favorable weather conditions, scientists have found.
The beautiful striking lady (Vanessa Cardui) butterfly was first shown to be able to make the 12,000-14,000 km round trip – the longest insect migration known to date – in greater numbers, when the wetter conditions of the desert help the plants on which it lays its eggs.
The findings of the international research team provide insight into how insects, including pollinators, parasites and the diseases they carry, could spread between continents in the future as climate change alters conditions seasonal.
Professor Tom Oliver, an ecologist at the University of Reading and co-author of the study, said: “We know that the number of Painted Lady butterflies in Europe varies enormously, sometimes with 100 times over year to year. ‘other. However, the conditions that caused this were unknown, and the suggestion that the butterflies could cross the Sahara desert and oceans to reach Europe has not been proven.
“This research shows that this unlikely trip is possible and that certain climatic conditions leading up to the migration season have a big influence on the numbers that do so. It shows how the wildlife we see in the UK can transcend national borders, and protecting these species requires strong international cooperation ”.
In addition to answering long-asked questions about butterfly migrations, the findings could help predict the movements of other insects that affect humans, such as the locusts currently plaguing East Africa or the mosquitoes that are vectors of the malaria.
Professor Oliver said: “We love to see the beautiful Painted Lady butterflies in our gardens in Europe, but climate change will also lead to changes in invasive species that are crop pests or those that spread disease. Food shortages in East Africa remind us that the impacts of climate change can be much more dramatic than a few degrees of warming might seem at first glance. “
La Belle Dame migrates in spring, after a winter breeding season. The researchers used long-term monitoring data from thousands of trained volunteer loggers, as well as climate and atmospheric data in parts of sub-Saharan Africa and Europe to learn more about their movements.
The study, published in the Proceedings of the National Academy of Sciences newspaper, found that increased vegetation in the African savannah during winter and in North Africa in spring, combined with favorable tailwinds, are the three most important factors in the number of migrants to Europe.
Lady’s caterpillars feed on the leaves of plants that thrive in wetter winter conditions in the savannah and Sahel regions of sub-Saharan Africa, causing the population to explode. They migrate across the Sahara, and when there are also wet and green spring conditions in North Africa, this allows for additional breeding and increases the number crossing the Mediterranean Sea to reach Europe.
The scientists’ simulations also showed that there are regularly favorable tailwinds between Africa and Western Europe, providing insects with opportunities for transcontinental travel.
The team calculated that the butterflies must fly nonstop during the day and rest at night to cross the Sahara, making stops to feed on nectar. This is similar to the model in which songbirds that fly at night migrate.
They concluded that the butterflies had to fly up to 1 to 3 km above sea level to take advantage of favorable tail winds, as their maximum autonomous flight speed of around 6 meters per second would make a crossing of the Sahara extremely hard.
Researchers used observations of similar butterfly species to calculate that Painted Ladies have enough body fat after metamorphosis to endure 40 hours of non-stop flight, and continue to feed on nectar whenever possible in order to cross. the Sahara.
The results may help improve predictions about which insect species might be found in different regions in the future as a result of climate change, and how many they might occur.
Reference: “Environmental drivers of annual population fluctuations in a trans-Saharan insect migrant” by Gao Hu, Constanti Stefanescu, Tom H. Oliver, David B. Roy, Tom Brereton, Chris Van Swaay, Don R. Reynolds and Jason W. Chapman , June 21, 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2102762118