Caterpillars Respond to Climate Change by Altering Feeding Habits

A study published in the journal Functional Ecology details how some insects are adapting to a hotter and more variable climate. Caterpillars of two butterfly species common in Colorado and California have been observed feeding in higher and broader temperature ranges over the last 40 years, suggesting that the creatures are responding to their changing environment.

University of North Carolina at Chapel Hill biologist Joel Kingsolver said the observations represent a rare instance of how recent changes in the climate affect physiological traits, such as the inner workings of how the body regulates feeding behavior.

"To our knowledge, this is the first instance where we show changes in physiological traits in response to recent climate change," said Kingsolver, who led the research.

To grow, caterpillars must eat. But the creatures can only eat effectively when it's not too cold and not too hot, Kingsolver said. In ideal temperatures, caterpillars can gain up to 20 percent of their body weight every hour by gorging on food with reckless abandon. These surges in growth will affect when the caterpillars form cocoons and when they emerge as butterflies, which will ultimately determine their reproductive success.

Kingsolver and his colleagues, including UNC graduate students Jessica Higgins and Heidi MacLean and the University of Washington's Lauren Buckley, compared modern species of sulfur butterflies (Colias) to their ancestors from 40 years ago, finding that the insects now have broader range for ideal feeding temperature and a higher optimal feeding temperature than they had in the past.

For their study, the researchers measured changes in climate at two sites in California and Colorado and compared that data to changes in the caterpillars feeding rates using current and historical data.

They found that temperatures at the two study sites had between a twofold and fourfold increase in days hotter than 82 degrees Fahrenheit between 1970 and now. As a likely response to these temperature fluctuations, modern caterpillars started to eat faster at higher temperatures, the researchers said. Moreover, the caterpillars in California were also documented eating faster at lower temperatures, even though their optimal feeding temperature did not change.

"These two species of caterpillars adapted to the increased frequency of higher temperatures over 40 years in two different ways, but both are better suited than their ancestors to thrive in a hotter, more variable climate," Higgins said. "Our climate is changing. The thermal physiology of these species is changing, too."