Mourning Cloak Caterpillar

The mourning cloak caterpillar is the larval stage of one of the longest-lived butterflies in North America, an adult that can survive nearly a year and is often the first butterfly seen flying in early spring. Unlike many solitary caterpillars, mourning cloak larvae feed gregariously in groups, especially in their early instars, which can make them highly visible on host branches.

The species is widespread across the Northern Hemisphere and is well adapted to cold climates, a trait reflected in both the overwintering adult butterfly and the hardy, communal caterpillars.

• Body is velvety black, densely speckled with tiny white dots
• A row of brick-red or maroon spots runs down the center of the back
• Covered in branched black spines (scoli) along the body
• Prolegs and head are black
• Larvae are often found feeding together in groups on the same branch, especially when young
• Similar in general form to other nymphalid caterpillars but distinguished by the red dorsal spots combined with white speckling

This species has a broad range across North America, Europe, and Asia, found in deciduous woodlands, riverbanks, parks, and residential areas wherever host trees grow. Caterpillars are most often seen in spring feeding on willow, elm, poplar, hackberry, and birch, sometimes defoliating entire branches when populations are dense.

Young caterpillars feed in tight groups on a single branch, spinning loose communal silk webbing, and disperse to feed more independently as they mature. This gregarious behavior can lead to noticeable defoliation of host branches, occasionally drawing attention as a minor garden or landscape pest. The spiny body provides some defense against predators, and the species is preyed upon by birds and parasitic wasps despite its bristly appearance. As an adult, the mourning cloak butterfly is notable for overwintering in bark crevices and emerging on warm winter days, extending its ecological activity well beyond the typical butterfly season.

Females lay eggs in tight clusters encircling a twig of the host plant. Larvae hatch together and feed communally through the early instars before becoming more solitary in later stages, developing through five instars over several weeks. The mature caterpillar forms a mottled gray-brown chrysalis, often hanging from a branch or nearby structure. The species typically produces one generation per year in cooler regions, with the resulting adult butterflies overwintering rather than the caterpillars, though warmer areas may see additional broods.