Mourning Cloaks

By Susan Benson,
CNHM Director of Education

The sun is shining, and the last of the melting snow trickles down the driveway. Fluttering down past me goes the first butterfly of the season. A butterfly, in March or April? The main coloration of this butterfly is dark purple-brown, with yellow edges on its wings. Its underside is mottled gray with a lighter yellow edging. It flies straight, flapping alternating with sailing as it moves along by us. This butterfly is a mourning cloak, and it is one of nature and spring’s first happy signs!

Mourning cloaks are named for their dark coloring, which resembles the traditional mourning cloak worn when someone is mourning. In truth, its dark colors warm it faster on the sunny spring days, allowing it to move about when most insects are still not capable of movement. They get warmed up through basking in the sunlight, as they need body temperatures close to that of humans in order to fly. Once they begin their flight their muscles provide enough heat to keep them going. This is passive solar heating at its finest.

Why are mourning cloaks the first spring butterflies? They overwinter as adults, having spent the winter in cryo-preservation. In the fall, mourning cloaks produce antifreeze proteins that they circulate through their blood. These proteins bind to the surface of tiny ice crystals to prevent them from growing bigger and harming the tissues. They also build up higher concentration of sugars, called glycerol, in their blood and tissues to lower the freezing point of their body. Finally, they hide in tree cavities, beneath tree bark, or under leaf litter. It is important, however, that they find a fairly dry place to overwinter so they can avoid contact with ice in the environment that surrounds them. This adult strategy is a different form of hibernation to be sure!

During the spring and summer, the adult mourning cloaks feed on tree sap, especially from oak trees, or fermenting fruit. Occasionally mourning cloaks will be seen at sapsucker holes feeding on sap, or at mud puddles or animal scat where they extract nutrients. When females lay their up to 250 eggs, they prefer willow, birch, aspen, or elm trees. The eggs hatch within about ten days, and the caterpillars are black with red and white spots, with bristly spines on their body. The larvae feed together in silk webs in their large family groups. If they overfeed and wipe out the food supply on the tree, they will move along single file in a line to the next feeding site. By mid-June they leave their host plants, and go off in search of a new site, where they pupate for about 10-15 days. They are believed to be one of the longest-living butterflies, living up to ten months as adults.

With these amazing early spring temperatures, be sure to get outdoors and enjoy the warm weather. Keep your eyes open for a chance encounter with this lovely butterfly. Perhaps you will be lucky and it will fly or land right near you.

For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at cablemuseumnaturewatch.blogspot.com.