The once rare brown argus butterfly is on the move, expanding its range and numbers in the U.K.—and it's all thanks to climate change.

Thus far, the world's climate has warmed roughly 0.8 degree Celsius over the course of the last century or so, thanks to a rise in greenhouse gas concentrations now approaching 400 parts-per-million. With that amount of warming, biologists expect some species ranges to expand and others to contract but, thus far, many wily animals and plants have been confounding scientists' expectations. In some cases, species that favor a warmer climate have actually retreated (think: lizards or amphibians). Or others have expanded even faster than the climate has warmed (think: tree species moving up a mountain slope).

Obviously climate change isn't the only factor in play. Habitat loss and disease seem to be dooming many varieties of amphibian while plants may be benefiting from human help (carried along on our own fossil fueled travels by car or plane).

But for the brown argus butterfly with its trademark orange and white spots near its wingtips, climate seems to play a key role. It has spread northwards nearly 80 kilometers in just the last two decades, according to the U.K. Butterfly Monitoring Scheme. Warm summers have allowed the butterfly to begin using a new type of plants—such as the dove's foot cranesbill—as a host in the U.K., the way it does in continental Europe. In prior decades, the butterfly had restricted itself to the rockrose.

That appears to be a result of the cooler climate back then. The long-lived and relatively sprawling rockrose plant allows for more stable populations of the butterfly when times are tough because of cool weather. It hosts the caterpillars on the underside of leaves on south-facing (and therefore sun-warmed) hillsides. But when generally balmy summers abound, as recently, the annual cranesbill can help the brown argus butterfly expand its range, according to new research to be published in Science on May 25.

Of course, this expansion in the north is counterbalanced by a loss of habitat further south, where conditions are rapidly becoming too hot for the butterfly. "The picture across its whole distributional range in Europe looks somewhat different," notes ecologist Oliver Schweiger of the Heimholtz Centre for Environmental Research in Halle, Germany, who was not involved in the research. His modeling work suggests that, even assuming the butterfly can fly past any natural features that might otherwise restrict range expansion, "large range retractions in the South cannot be counterbalanced by the expansions in the North." And even flying animals, like butterflies and birds, can't seem to keep pace with the poleward march of temperature bands, according to Schweiger's work.

Nevertheless, this kind of adaptation to a changing climate may offer hope for other species. "Not all species must necessarily suffer from climate change," Schweiger adds. "Showing that an extension of the utilizable host plants is possible and can help to cope with the consequences of climate change can be considered as good news." In other words, don't underestimate a species’ ability to adapt and make the best of it.

Image: Courtesy of Louise Mair