Mourningcloak butterfly or spiny elm caterpillar

Distribution

Canada

Micro-habitat(s)

Leaf

Damage, symptoms and biology

The observation of colonies of black larvae with red dots and spines on their backs provides evidence of the mourningcloak butterfly's presence. These larvae can defoliate the leaves right to the midrib. Other signs of the insect's presence include rings of eggs around defoliated twigs and chrysalids suspended from small branches or leaves. The defoliation caused by the larvae does not pose a serious threat to damaged trees.

The female lays her eggs in a ring around twigs. After hatching, the larvae migrate to the leaves and feed on them in small colonies, beginning with the blade portions between the veins and eventually consuming the entire leaf, except the midrib. They strip each branch of all its foliage before moving to the next one.

After the caterpillars cease feeding, they hang themselves from the lower part of a small branch or other objects and change into a chrysalid. The insect usually overwinters as an adult, but can also overwinter as a pupa.

Life cycle (East of the Rockies)

Other information

Native to Canada and recorded in surveys since 1936, the mourningcloak butterfly causes little damage to forests since it mainly attacks isolated trees and ornamental trees. Infestations are uncommon and of short duration.

To prevent an infestation on small ornamental trees, it is advisable to crush egg rings that have not yet hatched and to pick off and destroy any larvae found on the foliage.

Main host(s)

Balsam poplar, balsam willow, Bebb willow, black willow, feltleaf willow, golden weeping willow, heartleaf willow, hooker willow, hybrid white willow, laurel willow, littletree willow, Mackenzie willow, meadow willow, Pacific willow, peachleaf willow, pussy willow, sandbar willow, satiny willow, Scouler willow, shining willow, Sitka willow, trembling aspen, violet willow, white elm, willow