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Lake Simcoe Region Conservation Authority

Skip Navigation LinksLake Simcoe Region Conservation Authority > How to Deal with the Invasive Spongy Moth

​​close up of spongy moth catepillar on a leafUnwelcome Visitors in Your Yard: How to Deal with the Invasive Spongy Moth

Summer is here and Nature is getting ready to reveal her season's new looks. But underneath the warming temperatures, chirping birds and bursts of colour lurks something not quite so attractive: invasive species that can threaten the health of our local ecosystems.

Whether you're new to the topic of invasive species or have dealt with one yourself, it's important to get to know the current culprits in the Lake Simcoe watershed, and one in particular that's been of concern in the past few years.

What Are Invasive Species?

Invasive species are exactly what they sound like: they're non-native (alien) species of plants, insects or animals that invade a new area and cause ecological and economic harm to their new environment. Invasives can cause a number of issues, from reducing biodiversity to permanently altering habitats, and can even trigger the extinction of other species.

Invasive species vary widely, from seemingly-innocent insects to beautiful plants that people plant in their gardens without realizing. And with hundreds of different invasives in Ontario alone, there's no shortage of threats to our natural environment.

Introducing the Spongy Moth

Lymantria dispar dispar, now known as the Spongy Moth (and formerly known as the European Gypsy Moth), is a moth species native to Europe that was introduced to North America in the late 1800s.

Southern Ontario, from Sarnia to Ottawa and including the Lake Simcoe watershed, is currently experiencing an outbreak of this hardy moth species, which has been around long enough that it's considered naturalized in this area. Naturalized species are alien species that have established stable self-sustaining populations such that control/eradication efforts are not feasible. Recent monitoring by several agencies including the Ministry of Northern Development, Mines, Natural Resources and Forestry, indicates the current outbreak is in decline.

The Spongy Moth goes through a number of stages in its lifecycle, with the caterpillar stage being the time when most people take notice: these furry caterpillars devour leaves and create quite a mess. A few years of an outbreak and consequent defoliation can weaken trees, leaving them more susceptible to secondary pests, drought, and sometimes even death.

Dealing with the Spongy Moth Outbreak

There are a few steps you can take to reduce the impact of the Spongy Moth if you find them on your property:

  • First off you need to identify them. They are up to approximately 5 centimetres long with a row of five pairs of blue dots then a double row of six pairs of red dots.
  • The species lays dormant over winter, in light beige, spongy egg sacs that can be found on tree trunks and limbs, lawn furniture and even buildings. By scraping off and disposing of these sacs before they hatch in spring, you can help prevent a large number of Spongy Moths on your trees.
  • For the caterpillars that hatch, you can place burlap bands (with folds) around tree trunks to lure the caterpillars during warm days. Once the caterpillars collect in the burlap folds, scrape them into a bucket of hot, soapy water (ideally once a day).
  • Be sure to always wear gloves to avoid touching the caterpillars, as contact can result in a rash or skin irritation.
  • If you want to help a particular tree you think is under stress from defoliation, you can take other actions to help it. For instance, if it's been really hot and dry, you can water it.
  • The use of insecticides to try and control invasive species is problematic. It can end up contaminating the environment or harming other beneficial species if not used correctly. We recommend leaving this option to the professionals.

The Best Defence is Prevention

While the following advice can't stop species like the Spongy Moth that have already invaded, it can prevent their spread or the invasion of new species that haven't yet made it here. These steps should become part of your regular routine:

  • Make sure to research any plant before introducing it to your garden/property.
  • Never throw bait fish back in the water.
  • Always clean your boat before going to another body of water.
  • Never transport firewood out of your local area.
  • Clean your boots before hiking in different areas.

As you can see from the below graph showing the recent history of Spongy Moth outbreaks, this outbreak will eventually come to an end. For more information, visit our the ​spongy moth page on our website.​

a graph displaying the moderate to severe defoliation in ontario from 1980 to 2020 with 2020 peaking at 600,000 hectares

Will Climate Change Affect Invasive Species?

It's expected that climate change has the potential to make invasive species more problematic in the future. This is a very complex topic that we will discuss more in an upcoming issue. In the meantime, if you have specific questions about climate change and invasive species, please send them to us via email: communications@LSRCA.on.ca​

a side by side photo of trees defoliated July 2021 beside an August 2021 where the same trees have grown back with new leaves

​​This picture, taken from the York Region website, provides an example of how forests bounce back the same year, even after severe defoliation.