During the brief interlude of spring-like weather we had recently, even with patches of snow still on the ground, I spotted a butterfly flitting through the forest. It was a Mourning Cloak (Nymphalis antiopa), named long ago for its dark-brownish black wings colored like the cloak of a person in mourning.
How could this butterfly have gone through its life cycle—from egg to larva (caterpillar) to chrysalis to adult—in this cold weather? Well, it didn’t. The Mourning Cloak is one of the few butterflies that overwinters as an adult, taking shelter under bark or in a tree cavity.
How do they survive the cold? They go into diapause, a dormancy many insects undergo in which their systems shut down and their bodies produce glycerol, a kind of antifreeze that protects their vital organs from freezing. Most insects overwinter as eggs, as larvae or as pupae (the resting stage known as a chrysalis in butterflies and as a cocoon in moths).
Mourning Cloaks live long compared to most butterflies—up to 12 months. That they overwinter might be one reason. When the adults emerge in late winter or early spring, they will warm up in sunny patches. They also turn their bodies to the sunlight to absorb heat.
These butterflies emerge when few flowers are in bloom. Flowing tree sap, with sugars and proteins, are an important early food source for Mourning Cloaks. Later they feed on ripe and fallen fruits as well as the sugary exudate from aphids. They don’t seek nectar as much as many other butterfly species, but I have seen them nectaring on the catkins of Pussy Willow (Salix discolor) and Black Willow (Salix nigra). This is yet another reason to include native shrubs and trees such as these in your landscape. Native willows are an important early pollen source for many native bee species too.
Mourning Cloak males will look for an appropriate territory, a prime location to attract a female. On mating, the female will lay her eggs on leaves of larval host plants: willows, American Elm (Ulmus americana), Hackberry (Celtis occidentalis), ashes (Fraxinus spp.), poplars (Populus spp.), and birches (Betula spp.). They hatch about 12 days later. In early stages the larvae group together in a web, perhaps an adaptation for protection against predators. The caterpillars are black with spines and rows of red dots running down the center of the back, which might be aposematic, a warning coloration. If handled, those spines can sting.
After undergoing five instars (larval growth stages and sheds), the Mourning Cloak spends about two weeks as a chrysalis, before eclosing, or emerging as a butterfly in mid-summer. Adults who lived through the previous winter then die. This new brood is the future of the species.
How can you help this butterfly and other important insects to live long in your yard? Try to garden naturally without using pesticides. Don’t use butterfly boxes. They really don’t work and actually attract hornets, which can prey on butterflies. Allow a “messy” section in your yard, with bark and leaves for overwintering sites. Plant native trees and shrubs such as those mentioned here. We all can do our part to help this striking butterfly and many other important species to prosper.