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Harbinger of spring

April 5, 2012

I was on a hike on a trail in Shohola during mid-March when I spotted what appeared to be a butterfly flying in the distance. I waited and watched as it landed nearby. What butterfly flies around in March when it is still cold and several weeks from “greening up” time?

The answer was soon obvious as I got close enough to identify this dark-colored butterfly with a yellow fringe around its wings. I was looking at a mourning cloak (Nymphalis antiope) on a late winter jaunt. One of the nicknames for this species is “Harbinger of Spring.” It did indeed make an early appearance.

So how is it that the mourning cloak can grow so big first thing in the spring? The secret is part of its life cycle in the fact that it over-winters as an adult. It finds a crevice or a hollow in a tree to hide in the fall, and climate changes trigger a phenomenon known as cryo-preservation, where the mourning cloak’s body manufactures natural antifreeze compounds such as sorbitol and glycerol to keep ice crystals from forming during the winter.

These emerging adults may sometimes be seen on brief outings during warm spells in February. During spring, they find a mate, lay eggs and die soon after. The hatching caterpillars grow and eventually emerge from their chrysalis as adult butterflies in June or July. After a brief period of foraging, they enter a period of estivation (a period of summer dormancy) before they go active again in early fall to feed and store energy for winter hibernation and repeat the life cycle. Because of this lifecycle, this harbinger of spring lives for about 10 to 11 months, a long lifespan for a butterfly.