The amazing hibernating mourning cloak butterfly

Unlike the many butterflies that get out of town when the weather turns cold, the mourning cloak (Nymphalis antipopa) replaces some of its body’s water with antifreeze-like chemicals called glycols and looks for a safe spot to spend the winter months. So, as the snow and cold surround us, so do these gorgeous adult butterflies—their maroon wings rimmed in gold around iridescent blue spots set in black. They fold their wings to hibernate, and the undersides look much like their wintry surroundings—mottled and brown but for the yellow edge—a very effective camouflage.

You may find this species hiding under the loose bark of a tree, in a log pile, or between the boards of your backyard shed. And on warmer winter days, even as snow remains on the ground, mourning cloaks can emerge from hibernation to take a short flight before returning to their winter resting spot.

The mourning cloak has the longest lifespan of any of our butterflies, up to a year. It is a master of energy conservation and spends the hottest days of summer estivating, or slowing to a sleepy torpor and consuming no food.

And speaking of food, the mourning cloak’s diet follows its habit of flying at times when flowers may not be available. Like all of our butterflies, its days of munching solid food belong to its caterpillar stage. But rather than sipping nectar as its main source of energy, it fuels its flight mostly with tree sap (especially oak), or the juices of rotting fruit, and even dung. Rarely, it will visit flowers.

To support this beautiful butterfly, we must also plant and nurture the food their caterpillars depend upon: in the Chicago area, these include willow trees and shrubs, hackberry, cottonwood, and American elm.

Several other of our butterflies spend the winter as adults, including the question mark, comma, and tortoise shells.