Mourning Cloaks: Butterflies of Early Spring
By Sarah Millar
Broadcast 6.2009, 5.2015, and 3.20 & 3.23.2024

Mourning cloaks overwinter in Montana, and are one of the first butterflies to appear in spring. Photo by J.N. Stuart, CC BY-NC-ND 2.0.

 

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If you have ever spent any time with a three-year-old, then you have probably probably heard a lot of simple questions about the world around you. Here’s one that occurred recently.

While walking on a trail by our house earlier this spring, my daughter spotted several big black, fuzzy caterpillars. We carefully picked one up and inspected it. It was black, about an inch long, with white flecks and a row of reddish spots. It also had distinctive black bottlebrush-like spines.

My daughter has been learning a lot about bugs at preschool this spring and she excitedly told me that it was a caterpillar. I can just hear her now, asking endless “why” questions as I tried to explain to her that when caterpillars grow up they turn into butterflies. Without hesitating my daughter asked if she, too, could be a butterfly when she grows up.

I couldn’t help but wonder. What kind of butterfly will this caterpillar turn into when it grows up? After doing some research, we learned that in a few weeks this caterpillar will turn into a mourning cloak. Mourning cloaks are fairly common in Western Montana, and also happen to be our state butterfly. The name, mourning cloak, refers to its resemblance to the traditional dark-colored cloak worn when one was in mourning.

Mourning cloaks are members of the Nymphalidae family or, more commonly, the brush-footed butterflies. Members of this family are found worldwide. They are medium to large, typically with bright-colored wings. The front pair of legs on these butterflies are small, hairy, and “brush-like.”

Mourning cloak caterpillars feed in social groups on the leaves of several types of deciduous trees and shrubs, like cottonwoods, poplar, elm, birch, rose, mulberry, and several species of willow. Their distinctive spines and hairs protect them from predators, allowing them to feed in obvious groups. As they eat and grow, they shed their skin several times.

Eventually, mourning cloak caterpillars will leave the plant that they have been feasting on in search of a spot to pupate. They will form a spiky gray chrysalis, a temporary home in which they can undergo metamorphosis and become a butterfly. This process takes about 10-20 days, depending on the temperature.

In June or July, a whole new generation of adult mourning cloaks will emerge. These second generation butterflies will disperse further from their breeding grounds in search of food. They rarely feed on flower nectar but prefer tree sap as their form of nutrition.

Mourning cloaks have very deep red to dark brown wings, characterized by bright blue spots with a distinctive yellowish border.. They often rest on dark-colored bark, where they are camouflaged from predators. This protective coloration also allows them to bask in direct sunlight, which is important to butterflies like the mourning cloak that live in cold, mountainous areas, and especially those active in early spring. They need to warm up before they can fly, and they do this by opening their dark wings and angling their bodies toward the sun.

Mourning cloaks hibernate in winter, seeking shelter under bark, crevices, or in wood piles. They often are the first butterflies you’ll see in the spring, flitting around sometimes even before the snow melts and feeding on tree sap during the early chilly mornings.

Male mourning cloaks are territorial and you can often find them perched in sunny openings during the afternoon, waiting for a receptive female to fly by. The butterflies will die soon after mating, having spent as long as ten months as an adult, holding the record for a butterfly’s life span.

So while you’re walking in the woods this spring, keep an eye out for mourning cloak butterflies. And if you happen to be in the company of a three-year-old and they ask you where they come from, now you will have some answers.

 


Every week since 1991, Field Notes has inquired about Montana’s natural history. Field Notes are written by naturalists, students, and listeners about the puzzle-tree bark, eagle talons, woolly aphids, and giant puffballs of Western, Central and Southwestern Montana and aired weekly on Montana Public Radio.

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