One of our earliest flying butterflies, the mourning cloak (Nymphalis antiopa) overwintered under tree bark until bright sunny days brought it forth to sip flowing sap from broken tree branches. This largest member of the tortoiseshell family (Nymphalidae) is a common butterfly that can be found across much of North America. Since emerging from her hibernation, the female has mated and laid her tiny eggs in clusters along a branch or on the underside of a leaf.
Because mourning cloak eggs are laid in groups on their host plants, the hatched caterpillars can be seen feeding together. These gregarious caterpillars will remain with their siblings on their host plant of willow, elm, hackberry or cottonwood to munch on the tree’s leaves. They will continue feeding, growing and molting for about a month.
At full size, a mourning cloak caterpillar can be over two inches long. Its body is a deep black covered in white specks, with a row of cherry-red spots running down its back. A beautiful insect, until you notice the many-branched, shiny black spines daring you to touch it. It is probably safe to assume that this caterpillar is not on a bird’s list of first-choice meals.
Though the caterpillar’s spines can protect it from some predators, they do not prevent various parasitic insects from attacking it. Species of chalcid and ichneumon wasps, as well as tachinid flies, are known to parasitize the caterpillar by laying their eggs within its body. The hatching larval wasps and flies then feed on the caterpillar, which eventually dies.
When it is time for the mourning cloak caterpillar to transform into a butterfly (and it has been fortunate enough to avoid the parasites), it will leave its host plant to find an appropriate branch or grass stem on which to pupate. Its thorny brown chrysalis will hang upside down from the stem for about two weeks before a chocolaty-brown butterfly with a band of lovely blue spots and creamy yellow margins emerges.