The last leg of the longest butterfly migration has now been identified

Yearly, painted woman butterflies born in Europe embark south on an epic journey to Africa. Now, researchers know precisely the place on the continent these long-haul vacationers spend their winter trip.

From December by February, after flying throughout the Sahara within the fall, the orange-and-brown-winged bugs arrange camp and breed in savannas and highlands throughout central Africa, scientists report April 10 within the Proceedings of the Nationwide Academy of Sciences. Because the wet season brings greenery to the area, the butterflies and their caterpillar offspring feast on quite a lot of crops till their wintering spots dry up. Then the butterflies fly north to Europe.  

Pinpointing precisely the place painted woman butterflies (Vanessa cardui) overwinter and breed was the final unknown piece of their roughly 15,000-kilometer migration, says Gerard Talavera, an entomologist and evolutionary biologist on the Botanical Institute of Barcelona. The species — probably the most widespread butterflies on the planet — boasts the longest round-trip journey of any butterfly (SN: 6/20/18).

Painted girls aren’t the one bugs to make such lengthy migratory journeys, says Constantí Stefanescu, a butterfly ecologist at Museu de Ciències Naturals de Granollers in Spain who was not concerned within the examine. Understanding how these butterflies do it gives a framework to discover how different migratory bugs, together with damaging pests, make such treks (SN: 4/8/18).

Scientists knew that the painted girls went to Africa, however the place on the continent they waited out European winters from December to February was a thriller (SN: 10/12/16). The butterflies cross the Sahara and arrive in nations akin to Chad within the fall. Round November the bugs fly elsewhere, Talavera says, however it was unknown the place they landed.

Earlier than this examine, Talavera and colleagues had predicted that subtropical areas near the equator may present appropriate behavior. To know for positive, the researchers wanted to search out butterflies within the discipline.

From late 2017 by early 2020, Talavera and a global crew of researchers carried out fieldwork at all kinds of web sites throughout sub-Saharan Africa in the course of the months of December and January. One other 15 websites have been monitored year-round for about two years. In whole, the crew seemed for adults and their younger in 9 nations, together with Benin, Cameroon, and Kenya.

It was a giant guess that the crew would even discover the butterflies, Talavera says. Their most well-liked crops in Europe are well-known, making them comparatively straightforward to search out. However what crops the bugs may choose in Africa was a giant open query. Other than the earlier evaluation pointing towards the subtropics and realizing that the bugs want open areas over forests, the crew was stepping into blind.

“My fundamental fear was about that, not with the ability to really discover the species,” Talavera says. 

That fear was unwarranted. The researchers discovered greater than 2,700 caterpillars and practically 2,000 grownup butterflies, from as far west as Cote d’Ivoire and all the way in which east to Kenya and Ethiopia.

From September to November, the butterflies occupy semiarid savannas. As these areas dry up, the painted girls shift south to savannas and highlands in barely humid areas from December to February. Central Africa’s tropical rainforests cease the butterflies from going any farther south, Talavera says. “These butterflies don’t like moist areas.”

Discipline observations recommend that numerous breeding may occur in these barely humid savannas and highlands. Heat climate throughout the area might assist the butterflies reproduce extra rapidly than they do in some components of Europe, Talavera says, that means three to 5 generations is perhaps born in sub-Saharan Africa earlier than any surviving adults head north in February.

Figuring out the place painted woman butterflies breed might assist researchers perceive why there are occasional inhabitants booms with 100 instances as many butterflies in some years as others, Stefanescu says. In 2021, he and colleagues linked the phenomenon to rains in sub-Saharan Africa — maybe giving butterflies extra crops to cease and lay eggs on. However the a part of West Africa recognized in that examine is completely different than the place the newly recognized breeding grounds are, Stefanescu says. Now, scientists can confirm the hyperlink by taking a look at rainfall and different circumstances the place child butterflies are discovered rising up.

However the subsequent thriller Talavera’s group hopes to resolve is why painted woman butterflies make such a protracted journey in any respect.