An article co-authored by Ernest Williams, the Christian A. Johnson Excellence in Teaching Professor of Biology, appears in the current issue of the Journal of the Lepidopterists’ Society. “Overwintering clusters of the monarch butterfly coincide with the least hazardous vertical temperatures in the oyamel forest” presents the results of the authors’ study of the impact of temperature on the survival of monarch butterflies overwintering in Mexico.
Butterflies freeze to death when the temperature falls to several degrees below freezing. Williams and his collaborators found that the butterflies’ lowest risk of freezing is at intermediate heights within the forest – the heights at which the butterflies form dense clusters. Research also showed that dense forest is better at insulating the butterflies from low temperatures than is thinned forest. For this reason, the researchers conclude, it is important to protect the high elevation fir forests in Mexico’s monarch butterfly biosphere.