Gypsy Moth, also known as Spongy Moth and LD Moth (Lymantria dispar)

Impact – This moth is a non-native insect from Europe. Gypsy moth caterpillars feed on a large variety of trees including oak (preferred), maple, apple, hickory, basswood, birch. pine, spruce and more. In 2021, our region had a significant outbreak with major tree damage. Populations rise and fall in cycles, varying from very few to large numbers with noticeable leaf damage and tree defoliation. Populations can reach destructive levels – thousands of trees. Defoliation reduces the resistance of trees making them more susceptible to pests and diseases.

What it is – Gypsy moths were accidentally introduced in 1869 when they were brought to the US to potentially develop a silk industry. Caterpillars emerge from eggs in early spring when they begin feeding. Eggs are laid in mid-summer and overwinter. They will feed on the trees above but when limited they may attack evergreens which will not regrow leaves as easily as deciduous trees. Outbreaks are cyclical. Most healthy trees can withstand a year of leaf loss dependent on how much defoliation took place.

How to identify – The larval stage of the moth is a caterpillar. They grow to about 2 ½ in., have pairs of raised blue spots followed by six pairs of raised red spots along its back. The hairs on their backs can cause skin irritation in some people. Females (do not fly) are white with brown markings and males are brownish. They may spin long silken threads on which they drop from foliage. Buff color egg masses contain 75-700 eggs & can be found on tree trunks.

Control – Caterpillars are naturally controlled by birds, parasites and diseases. In large forested areas, manual removal in not practical. When populations are low, caterpillars can by killed by squishing them. Destroy egg masses by scraping them into a container of detergent for 2 days. Some publications have reported that eggs may survive if just scrapped on the ground. In April/June, sticky barrier bands or burlap folded over a cord may be placed around the tree trunk.

Various insecticides for gypsy moths are available at garden centers. Microbial insecticides made from naturally occurring bacteria, viruses, etc. The Bt subspecies kurstaki (Btk) is the most appropriate for control and must be applied to the leaves. Other chemical insecticides can have an adverse impact on beneficial insects such as bees and is not effective against moth pupae, egg masses or caterpillars. Horticultural oil insecticides (Neem), also non-selective but safer for humans and animals when saturating egg masses in late March – April before the caterpillars emerge and again in October to early November. Pheromone moth traps are not effective in controlling populations as they only attract males and benefit only the seller.