By Megan Hart, Park Biologist
Most of us can’t wait for the first warm days of spring. The rays from the sun seem to give the world renewed life and purpose. The renewal of the season especially holds true for the mourning cloak butterfly (Nymphalis antiopa), which is often one of the first butterflies to be seen in spring. The mourning cloak is easy to identify with its dark maroon upper parts bounded by a black band with light blue spots and ending in a yellow strip at the bottom of the wings. When its wings are folded together, the underside looks like charred wood with a pale border, which allows it to blend in well with its surroundings in the forest. The solemn name for this beautiful sign of spring comes from the coloration of its wings, which is said to look like a cloak that was historically worn during periods of bereavement and mourning.
Mourning cloak
How are mourning cloaks able to be seen so early in spring before most plants have really started to grow? These butterflies use a couple of tricks to help them survive the changing seasons for almost a year—a fairly long life for a butterfly. Each year’s new adults emerge from their cocoons in July. These new adults then undergo a summer hibernation, or aestivation, until fall when they begin feeding mostly on tree sap and rotting fruit to prepare for winter. Once winter arrives, these butterflies hide in crevices and under the bark of trees and undergo a form of winter hibernation until temperatures get warm enough for them to emerge. Mourning cloaks begin to come out from their hiding places once temperatures stay around 60° Fahrenheit. In order to fly, their internal body temperatures must reach 65° Fahrenheit. To accomplish this, they shiver their flight muscles at high rates–they can raise their body temperatures 15 to 20 degrees in just a few minutes! They then go out in search of food, mates, and to lay their eggs on preferred plant species like willows, cottonwood, birch, poplars, hackberries, and elms.
After the eggs hatch, caterpillars stay together in a family group on the same plant, eating and growing rapidly. The caterpillars tend to stick together to confuse predators by shaking or vibrating in unison if they feel threatened. If this scare tactic doesn’t work, they are covered in spines that make them painful and difficult to pick up and eat. If the host plant they were hatched on does not provide enough food, you can see these caterpillars marching off in a line to find another food source, staying as a group as they travel. The caterpillars continue to stay together until they have reached their full size and leave their host plant usually in a mass migration to find a secluded place to make a cocoon. In just 10 to 15 days, a new adult mourning cloak will emerge and the cycle begins again.
Mourning cloaks can be found in forests and in a variety of open habitats. If you are interested in finding these unique butterflies, you are most likely to see them in their spring flights from April to May and in their fall flights from August to October in any of the parks (Chapin Forest Reservation is an especially good place to look). Keep your eyes out for early-flying butterflies—they may just be mourning cloaks!