Butterflies that remain in New England during the winter spend it in one of many stages – some as eggs, others as larvae or pupae, and a few as adults. Mourning Cloaks, Compton Tortoiseshells, Milbert’s Tortoiseshells, Question Marks, Gray Commas and Eastern Commas all overwinter as adult butterflies. They store fat in their bodies in the fall and replace a portion of the water in their blood with an antifreeze agent, which prevents the lethal formation of ice crystals in their bodies. These butterflies then slip into cracks, behind loose bark, in a hollow tree or some other sheltered spot where they enter a stage referred to as winter diapause. Metabolic and respiratory rates are greatly reduced, and the butterflies remain inactive until the warming, lengthening days of March and April, when they emerge to mate and lay eggs. They often look rather tattered, as they put many miles on their wings the previous summer. Unlike most adult butterflies which live only a few weeks, butterflies that overwinter as adults have a lifespan of eight to ten months. (Photo: Eastern Comma – note white “comma” on under side of hindwing)
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Mourning Cloaks have recently emerged from under loose bark where they hibernated all winter. These early flyers, along with a few other species such as commas and tortoiseshells, have a jump start in the spring due to their not having to go through metamorphosis like most butterflies. Born last summer, Mourning Cloaks live for roughly ten months (longer than most butterflies), overwintering and breeding and laying eggs soon after appearing in the spring. This summer their larvae will feed on willows and poplars before pupating and emerging as adults in time to seek shelter for the winter. With snow still on the ground, nectar is quite scarce, leaving butterflies that are active this time of year dependent on tree sap available where branches have broken for much of their sustenance.