Mild winters are detrimental to butterflies

William G. Gilroy in the Notre Dame News: The recent mild winter throughout much of the United States was a cause for celebration for many. However, butterfly aficionados shouldn’t be joining in the celebration. A new study by Jessica Hellmann, associate professor of biological sciences at the University of Notre Dame, and researchers from Western University found that mild winters, such as the one many of us just experienced, can be taxing for some butterfly or possibly other species.

Hellmann and her fellow researchers studied caterpillars of the Propertius Duskywing butterfly, which feed on Gary Oak trees. This species of caterpillar, like many insects, has a higher metabolic rate and burns more fat during mild winters.

“The energy reserves the caterpillars collect in the summer need to provide enough energy for both overwintering and metamorphosing into a butterfly in the spring,” Caroline William, lead author of the study, said.

So a butterfly needs to conserve as much energy as it can during the winter months. In the paper, Hellmann and her colleagues explain for the first time how warmer winters can lead to a decrease in the number of butterflies.

However, Hellmann and the Western University researchers found that warmer winters might not always reduce butterfly populations as much as one might initially think. They reared caterpillars in two different locations: one which often experiences more variable and warmer winter temperatures and one which generally features more stable and generally cooler winter temperatures. The caterpillars that were exposed to the warmer and more variable conditions were better able to withstand the warmer conditions, simply by being exposed to them. They did so by lowering the sensitivity of their metabolism....

Dreamy Duskywing (Erynnis icelus), Ottawa, Ontario, shot by D. Gordon E. Robertson, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license