Montana Public Radio

Bug Bytes: Mourning Cloak Butterfly

Feb 5, 2019

If you live in our northern states, some years spring can’t come soon enough. Seeing your first butterfly of the year must be a sure sign that spring has sprung — unless it’s a mourning cloak butterfly.

Mourning cloaks are a type of tortoiseshell butterfly. Along with a handful of butterflies known as anglewings, tortoiseshells are the first butterflies we see flying in late winter or early spring.

So how can mourning cloaks be flying about when there is often snow on the ground and we are weeks away from any hint of a flower? They have a few tricks up their tiny sleeves.

First, the adult butterflies hibernate during the winter. As cold weather approaches, they search for a hibernaculum — a safe place to hibernate, like a tree cavity, underneath some loose bark or underneath leaf litter.

But a safe place is not enough. They survive freezing temperatures through a process called "cryo-preservation"; basically, building up the equivalent of antifreeze in their cells to prevent the killing formation of ice crystals.

Since they can survive the winter as adult butterflies, as soon as the weather is warm enough, they take flight in search of food and a potential mate.

Unlike most other butterflies, they prefer a diet of tree sap, allowing them to become active long before any flowers are in bloom. They’ll also feed on rotting fruit, and the nutrients they get from animal scat.

When and if the weather turns cold again, they’ll resume their winter slumber, waiting for the return of warmer days.

So don’t let the wondrous sight of the season’s first butterfly fool you into thinking that spring is here. But it is a sure sign of things to come.

BugBytes is made possible by the Missoula Butterfly House and Insectarium, and Montana Public Radio. This show is also supported by funding from the Greater Montana Foundation: Encouraging communication on issues, trends and values of importance to Montanans.