Spongy Moth

A destructive pest threatening forests

What is it?

Spongy moth (EGM; Lymantria dispar dispar) is an invasive and destructive pest that poses a risk to deciduous and coniferous tree species.

Trees at risk

Spongy moth has over 300 known plant hosts, including many hardwood and some softwood tree species. Favoured tree species include oak (Quercus spp.), maple (Acer spp.), birch (Betula spp.), white pine (Pinus strobus), and white spruce (Picea glauca).

Impacts

A single spongy moth caterpillar can eat one square metre of leaves in a season
- Repeated defoliation makes trees susceptible to other pests and diseases, and can eventually lead to tree death

Defoliation in orchards can increase vulnerability to agricultural pests and diseases and can negatively impact farm stock

Loss of species in natural areas can affect biodiversity and forest wildlife

Life-Cycle

Eggs: Tan-coloured and can be found on tree trunks, bark, or other hard surfaces. Egg masses are about 4 cm and contain 100- 1,000 eggs.

Larvae: Charcoal grey with a double row of five blue and six red dots on its back. This is the life stage that causes defoliation.

Adult females: Larger than males with white colouring and dark zig-zag markings. Adult females are flightless.

Adult males: Greyish-brown with dark markings and can fly and survive about one week, mating with several different females.

How to manage Spongy Moth

For private homeowners, Btk (Bacillus thuringiensis kurstaki) is available for purchase from local hardware stores to use against EGM. This biopesticide can be applied by a registered pesticide application company or by homeowners who have carefully read application instructions. Btk is a product that affects the digestive system of caterpillars and should only be applied between May and early June, when EGM are still in the larval (caterpillar) stage. Two spray applications are usually required for effective control. Application of Btk after mid-June is not an effective way to manage EGM.

Spongy moth populations are also affected by a number of pests, including mice, birds, wasps, and a specific fungus and virus. The fungus and virus are believed to be the reasons gypsy moth populations crash for ten or more years.

CAUTION: Spongy moth caterpillars have long hairs that can cause skin irritation or allergic reactions for some people. For safety, use gloves while handling caterpillars.