The Painted Lady is pretty, with pointed salmon-pink wings. She looks delicate. Don’t be fooled by her name or appearance.
This is one rugged butterfly.
Like the Monarch, which travels from Canada to Mexico annually, the Painted Lady turns out to be part of the lepidopteran elite, with migration patterns similar to those of birds. In fact, she takes the crown from the Monarch, for the world’s toughest long-distance traveler, winging it all the way across the Sahara desert under extremely difficult conditions.
A study published in Biology Letters (paywall) shows that the Painted Lady travels nearly 3,000 miles, sometimes fluttering her wings against the wind, along a difficult migration route previously believed to be reserved for birds alone. “Very few insects are known to endure annual trans-Saharan circuits, but the Painted Lady butterfly (Vanessa cardui) is an exception,” the researchers write.
To reach this conclusion, a team from the Institut de Biologia Evolutiva in Spain, the University of Ottawa in Canada, Harvard University in the US, and the Israeli Lepidopterists Society, traced the migrations of butterflies in six regions—Morocco, Andalusia, Catalonia, Crete, Egypt and Israel—over three years, 2014-2017. They observed the butterflies’ behavior, of course, and studied the wind trajectories they flew on. Since the small wanderers are hard to tag with sensors, the scientists also used a unique method to figure out the origins of the traveling butterflies. They examined the chemical signature of soil and water from their birthplaces that’s left on the creatures’ wings.
That geographically specific hydrogen isotopic signature
Clement Bataille of the University of Ottawa, explained the unusual approach to Quartz. Basically, the researchers examined hydrogen isotopes left in the butterflies’ wings from the plants they ate to trace their origins. The scientists chose this method because they knew that water molecules from different regions behave slightly differently depending on their isotopic composition. The rain that falls in the African tropics has a different proportion of hydrogen isotopes from rainfall in Europe. Because of this, plants that develop in the tropical regions of Africa, taking in local water with its specific hydrogen isotope signature, will bear a particular chemical composition that is passed on to the plants that grow in the soil there and the creatures that eat them.
When caterpillars eats local plants, they inherit the geographically specific hydrogen isotopic signature, which is ultimately transmitted to the butterfly. “What we saw was that a large proportion of these individuals have an isotope signature in their wings that look like the Afrotropics,” Bataille says. “The conclusion is that a lot of the butterflies that end-up populating the Mediterranean region come from the Afrotropics.”
Making the most of their month on Earth
The chemical method of examining the butterflies’ origins helped to clear up a mystery about Painted Lady migration that observation alone could not. Previously, researchers thought that the butterfly’s offspring remained in Africa, traveling within the continent where they were born, creating a kind of “dead-end scenario” as far as migration goes. Now we know that’s not so and that the butterflies follow a circuitous route seasonally, with new generations going back and forth, as if headed “home”—though that home is not actually the place where they were born.
“We conclude that a dead-end scenario for the late autumn colonization of the Afrotropics can be discarded. While some specimens might integrate within alternative migration routes within Africa, a large portion of the population migrates back towards Europe remaining within the Africa–Europe migration circuit,” the scientists write.
These tough butterflies don’t live long—only one month. But they do go far. Researchers believe that the annual distance travelled by a Painted Lady’s successive generations may reach 7,500 miles, including crossing the Sahara desert twice in a single year.
While the paths may vary somewhat from journey to journey, depending on rainfall and available food at any given point, it’s now apparent that Painted Lady generations continually migrate a similar looping route. It’s very likely then, Bataille says, that the butterflies are genetically coded to orientate and navigate, following a predetermined path but making adjustments depending on circumstances.
Though traveling across the Sahara is notoriously difficult, it apparently comes naturally to these tiny winged creatures. Perhaps the time has come then for the Painted Lady to be seen as the new lepidopteran queen.
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