INFLUENCE OF TEMPERATURE, SURFACE BODY MOISTURE AND HEIGHT ABOVEGROUND ON SURVIVAL OF MONARCH BUTTERFLIES OVERWINTERING IN MEXICO

We examined the interaction of ambient freezing temperatures, dew formation on the body surface, and perch height on monarch butterflies' survival. We demonstrate that crawling up on the understory vegetation not only directly lowers freezing mortality by reducing exposure to freezing temperatures, but it also reduces the likelihood of dew formation followed by invasive freezing, that nullifies the monarch's supercooling ability. Monarchs that crawled 30-40 cm above the ground did not suffer freezing mortality, even when wet and exposed to -8.0-degrees-C. Thus, monarchs that are stranded on the ground when it is too cold for them to fly can greatly reduce freezing mortality by crawling up the understory vegetation.