Birch, Elm, Hackberry, Linden pine, Poplar and Willow
Appearance and Life Cycle
Adult mourningcloak butterflies emerge in early spring, just as most trees are breaking bud. Adults are dark, reddish-brown, with the outer edge of the wings bordered with a creamy yellow band enclosing a row of blue spots. The butterflies have a wingspan of 60-80 mm. Females deposit their eggs in masses of 300-450 on twigs and limbs of host trees. The eggs are ribbed, yellow to orange at first, changing to a dark brown or black later. Larvae emerge and feed as a group until almost full grown. Larvae, commonly known as the spiny elm caterpillar, are strikingly marked. They are black, marked with numerous, minute, white dots and a row of red spots down the centre of their back. They are covered with many spines which appear sharp and dangerous, but are harmless. Once full grown, approximately 50 mm long, the larva attaches itself to a twig and forms a chrysalis. Adults emerge soon after pupation and, depending on location, will either produce another generation or seek a hibernation site. In southern parts of the prairies, the mourningcloak butterfly is able to complete two generations per year, allowing the defoliating larvae to be present from May to September.
Damage occurs during the larval stage as caterpillars feed on the leaves. The spiny elm caterpillar is of minor importance in the forest, but is sometimes injurious to ornamental and shelterbelt trees.
Infestations can be controlled by removing and destroying infested twigs and branches. Populations are reduced by numerous parasites and several birds. Chemical control is rarely required, but carbaryl or malathion is effective.
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