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Scientists from the Institute of Evolutionary Biology have chased the Vanessa cardui butterfly across Africa to study its migration. Its results show that it is capable of crossing the Sahara desert and breeding in the African savannah traveling thousands of kilometers. This route is common in many birds, but it is the first case where it is shown that a butterfly can do the same.
The Vanessa cardui butterfly is an insect that makes a one-way trip between Europe and Africa every year. Until now, it was known to disappear from Europe in the fall and was thought to settle in North Africa for the winter. Now, thanks to field expeditions in Africa by scientists from the Barcelona Institute of Evolutionary Biology, a joint center of CSIC and UPF, and Harvard University (USA), it has been shown that it can reach the tropical savannah africana, that is, it makes a journey of 4,000 kilometers.
The insect not only withstands a very long journey, but also crosses mountains, the Mediterranean and the Sahara desert. Thus, despite having a fragile appearance, it can withstand extreme temperatures and orient itself while flying at high altitude. It feeds on a wide variety of plants, including thistles, to which it owes the popular name of cardera.
Gerard Talavera and Roger Vila, the researchers in charge of the study, spent an entire autumn touring countries such as Senegal, Benin, Chad and Ethiopia looking for specimens of this species. During this expedition they were able to observe a massive migration of thousands of carderas heading south into the Sahel. In Benin, in a single field on the Niger riverbed, they found more than 20,000 butterflies emerging from the chrysalis. These observations imply that the annual migratory range of the species is twice what was previously believed.
Such a long and complicated journey may not be an easy lifestyle, but some animals are forced to do so in order to exploit the resources of each season of the year and to ensure a favorable climate. As for butterflies, the best known example is that of the monarch butterfly, which travels from Canada to Mexico in massive groups.
A unique case among insects
“The case of the migration of Vanessa cardui is unique among all insects. It is the species of butterfly with a more cosmopolitan distribution and makes migratory circuits around the world that are practically unknown to us. His dispersive abilities are impressive. The migrations between Africa and Europe that we now know are only the tip of the iceberg of all the migrations that it is surely capable of doing in other parts of the world ”, explains Talavera.
According to Vila, it is a well-known and well-studied phenomenon in some birds that migrate between Europe and tropical Africa. “Now we have been able to show that at least one species of butterfly, the cardera, is also capable of such an extreme journey. To study them in Africa, we often crossed the Sahara desert by plane and I remember that, looking at the vast sand of thousands of square kilometers from the window, I thought that we were trying to demonstrate something practically impossible ”, emphasizes Vila.
The results are published today in the Biological Journal of the Linnean Society and tell the prodigious story of the migration of the carderas and the interesting expeditions that led to their discovery. The study has the support of the National Geographic Society and the European Union for the value of this project for the knowledge of such a peculiar adaptation and for the conservation of this unique butterfly.