nun moth

Lymantria monacha (Linnaeus)

Synonym(s): black arches, black-arched tussock

Nun moth is a native of Europe. It is not known to be established in North America. Egg masses on crates, pallets of other packing materials are the most likely route of entry. Hosts include Scots pine (Pinus sylvestris) and Norway spruce (Picea abies); however, the majority of conifers and broad-leaved tree species may also be hosts. Mated females deposit eggs in bark crevices under scales or lichens. The round eggs have a diameter of about 1/16 of an inch and are grayish brown. In late April or early May (at a temperature of about 50 – 60 °F) young caterpillars hatch, climb to the crown, and feed on young needles and male flowers. The newly hatched caterpillars are 1/8 of an inch long and have long hair that disappears after the first molt. Caterpillars molt 5-6 times. After the third molt, caterpillars gain their characteristic color. Caterpillars, characteristically, have a grayish-yellow head with black and brown spots, and bodies dark with light spots on the third, seventh, and eighth segments. There are tufts of hair of various lengths on the sides of the body. One caterpillar can damage about 300 Scots pine needles or 1,000 Norway spruce needles during its development. If a spruce tree is defoliated more than 50% it usually dies, however the Scots pine is more resistant than most conifer species. Pupae are 1/2 to 3/4 of an inch long. They change from green to dark brown/metallic black and develop tufts of white hair. Adults emerge and swarm from July through August and sometimes into mid- September. During the day the moths usually stay on lower parts of tree trunks, and at night males fly up to a third of a mile to find females. Females are 1/2 to 3/4 of an inch long with a 1 3/4 to 2 1/4 inch wingspan, and males are about 1/2 of an inch long with a 1 1/3 to 1 3/4 inch wingspan. Female antennae are thread-like, while male antennae are comb-shaped. The forewings of both sexes are white with wavy, dark bands. The hindwings are brownish-gray. However, color varies from white to dark forms.

Identification, Biology, Control and Management Resources

The Atlas of Forest Insect Pests - The Polish Forest Research Institute