*Note we are transitioning to the term Spongy moth following the announcement officially dropping the name “gypsy moth”.

What is the Spongy moth

The Spongy moth is an invasive and destructive pest that severely defoliates deciduous and coniferous trees and poses a risk to tree health. Caterpillars, which hatch in April to June, pose the largest threat to our tree population since they eat leaves. During severe outbreaks, large populations can completely defoliate trees and shrubs. While some trees can produce new leaves over the summer, the damage caused by losing their leaves can reduce their growth. Repeated defoliation causes affected trees to lose their strength and can eventually lead to tree death.

The Spongy moth goes through various life stages. Spongy moth egg masses overwinter on the bark of trees and other hard surfaces. In the spring, eggs hatch and caterpillars feed on leaves. By the time the caterpillars are mature in July, feeding is complete. Mature caterpillars transition to short-lived moths in July and August to reproduce and lay their soft egg masses. Up to 1,000 Spongy moth caterpillars can hatch from a single egg mass.

What can you do

Depending on the time of year and life stage there are several options to control the Spongy moth. Always wear gloves when handling the caterpillars because their hairs can cause skin irritation.

Destroy egg masses

From August to mid-April, you can destroy egg masses to prevent Spongy moth damage on your property. Egg masses can be found on tree trunks, branches, rocks, fences, and other hard surfaces. Scrape the egg masses into a container of soapy water and soak for one week before disposing.

Burlap band

From mid-May to June, use twine to loosely tie the burlap to the tree so that the top of the band hangs over the bottom. The burlap band acts as a hiding spot for caterpillars during the day. Check the bands daily and dispose of any caterpillars in a bucket of soapy water.

Hand pick

From July to August, pick pupae by hand with gloves and dispose into a bucket of soapy water. Soak the pupae for one week before disposing.

Biological control

From mid-April to mid-May, you can apply the biopesticide BTK (Bascillus thuringiensis) on leaves. BTK is a bacterium found naturally in the soil that is poisonous to the larvae once ingested. Use BTK under your own discretion and call a licensed contractor for application. Private landowners may arrange an aerial spray application of BTK by a licensed applicator.

Natural population control

Over the next several years we can expect the current Spongy moth outbreak to naturally collapse thanks to predators and pathogens. For example, NPV (nuclear polyhedrosis virus) is a viral infection that spreads quickly through large populations. The larger the population of Spongy moths, the easier it is for NPV to spread and cause a population to collapse. There is also a fungus (Entomophaga maimaigi) that has been introduced to control populations of Spongy moths. Infections are more likely to spread in a wet spring.

Spongy moths in Lanark County

We are providing education and awareness about the Spongy moth and how to reduce infestations on your property through Facebook (@LCClimateAction), factsheets, outreach, and more.

We are not actively managing Spongy moth populations. Not managing pest populations is a common, practical approach because pest outbreaks come and go naturally. This is largely due to predators, parasites, and pathogens that decrease Spongy moth populations and leads to their eventual collapse.

Additional resources

Spongy Moth Factsheet


Invasive Species Centre

Eastern Ontario Model Forest

Government of Ontario

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