Baseline Pollinator of the Month — Mourning Cloak Butterfly

April 4, 2022

Written by Amy Yarger, Butterfly Pavilion Horticulture Director

Most of us think of butterflies as colorful, even gaudy. We imagine them frolicking in the warm summer sun without a care in the world. This month’s pollinator, however, is a butterfly of a different stripe altogether. The mourning cloak butterfly (Nymphalis antiopa) wears dark, mysterious colors and prefers shady glens when the days are still springtime cool. Found in North America and Eurasia, this butterfly is named for its velvety maroon wings ornamented with gold edges and metallic blue spots – something a particularly elegant person might wear to a funeral. However, if you think this butterfly looks too jaunty for such a sad name, you can call it by one of its other many names: the Camberwell Beauty, the Grand Surprise, or the White Petticoat.

Members of the brush-foot family, mourning cloak butterflies have reduced, brush-like front legs. What sets them apart from their cousins, however, is the way they overwinter as adults. On warm late winter or early spring days, we may see these beautiful 4” wide butterflies feeding on tree sap or aphid honeydew. Unlike many butterflies, mourning cloaks prefer shadier, cooler spots and emerge early in the spring. During April and May, territorial males seek females to mate with. They select a spot, such as a sunny perch near a ditch or the edge of a stream, that females might like to visit, and then they go on patrol, waiting for that perfect female to arrive.

After mating, the female lays dozens of yellowish-green eggs on new shoots of willow, cottonwood, hackberry, birch, elm, or aspen trees. Caterpillars are mostly dark with black spines and orange spots along the top edge; they feed in social groups, relying on their formidable appearance to keep predators at bay. Their predators may include ants, wasps, praying mantids, and birds. When they are ready to pupate, the caterpillars then migrate away from their food plants and turn into brownish-gray, spiky chrysalids, which blend in very well with vegetation. By June or July, these caterpillars have metamorphosized into new adults, just as the last generation is passing away. Very few other butterfly species can live for a year like mourning cloaks can!

You won’t find these new adults in the summer heat, however – they find a safe spot, often under loose bark or in tree cavities, to rest in dormancy through fall and winter, emerging to mate and start the cycle all over again in the spring. On sunny mornings, they may open their dark wings and angle their bodies toward the sun to warm up their flight muscles. These butterflies have all sorts of tricks to defend themselves against their enemies, including playing possum, making loud clicks, and flying menacingly toward birds and other butterflies.

Mourning cloak butterflies, in their worldwide range, are usually thought of as mountain dwellers. However, we see them at our elevation as well. In this area, you are more likely to see this butterfly near creeks and wetlands – anywhere mature cottonwoods and willows grow. They benefit from open space, healthy trees, and clean water, just like we do. When we see a mourning cloak butterfly, we know that spring is on its way. We can also tell that our riparian forests are well established enough to support their offspring. The people of Montana appreciate this denizen of the woods so much that they declared the mourning cloak their state insect in 2001.

Gardeners can do a few things to help this gorgeous insect. When selecting a tree for your landscape, consider a hackberry or disease-resistant elm variety that can also provide food for the larvae of the morning cloak. Delay garden cleanup until May whenever possible, so that these butterflies can find shelter on cold nights. And finally, avoid using pesticides. Mourning cloaks aren’t picky but they are extremely sensitive to chemicals in their diet.

Want to learn more about pollinators and how to help them? Contact Butterfly Pavilion’s horticulture department at habitat@butterflies.org!