Global warming is changing how caterpillars eat

By John Upton

Animals can evolve to survive global warming by changing their behavior and by changing their bodies. Butterflies are particularly sensitive to climate change, and changes in their behavior have been well documented — most notably in their migration patterns and ranges. North American Butterfly Association president Jeffrey Glassberg recently told the Maryland Independent that climate change is affecting Rhopalocera on a vast scale. “There’s a whole suite of butterflies whose ranges are retreating,” he said. (Such changes are the subject of Flight Behavior, a novel by Barbara Kingsolver dealing with climate change.)

And now comes the first evidence that butterfly larvae are changing the internal workings of their bodies to help them cope with warming temperatures.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

University of North Carolina scientists studied the optimal feeding temperatures of Colias spp. caterpillars from California’s Sacramento Valley and Colorado’s Montrose Valley. The frequency of very hot days and nights at both sample sites have increased since the 1970s, when a similar study with the same caterpillar populations was conducted. Caterpillars feed best within specific temperature ranges, and the researchers discovered that the caterpillars have evolved to feed at higher temperatures. The results of the study were published in the journal Functional Ecology:

This study is among the first to show population changes in physiological performance in response to recent climate change, although previous theoretical work has predicted such changes. While previous work has highlighted adaptation to seasonal timing, specifically photoperiodic cues, our work suggests that rapid adaptation to changing thermal regimes may also be an essential mechanism.

I asked lead researcher Jessica Higgins whether she thinks that butterflies are among the first organisms to adapt their physiologies to warming conditions — or whether she thinks this was just the first time that such changes have been detected by scientists.

“I do think that other organisms may be adapting, but we can’t detect it because of the lack of good historical data,” Higgins said. “What made my experiment so unique was that I had this snapshot of caterpillar physiology back in the 1970s. I was able to compare my results with what they previously found and then correlate it with temperature. I think my study highlights that there can be adaption to physiological traits — not just changes in seasonality, which has been the main focus of previous adaptation-to-climate studies. “