Spongy Moth

Spongy moth* or Lymantria dispar dispar, formerly known as ‘gypsy moth', is an invasive insect first detected in Ontario in 1969. Spongy moth caterpillars feed on tree leaves and are present across southern Ontario, including in the City of Cambridge.

Figure 1: spongy moth caterpillar stage

When populations are high, they can defoliate whole trees and forests in a short amount of time. Spongy moth prefer oak trees, but will feed on a variety of hardwood tree species.

Typically, its populations peak every seven to ten years, and will reduce through natural causes. Under normal circumstances, defoliation caused by these insects won’t kill a tree. However, trees can decline to the point of death in some cases when defoliation is coupled with dry hot summers or impacted by other forest pests.

*The Entomological Society of Canada adopted the name of ‘spongy moth’  to acknowledge the spongy egg masses that the insect produces. The name was changed from its previous commonly known name because it contained a derogatory slur. As part of our commitment to diversity, equity and inclusion, the City of Cambridge uses the name ‘spongy moth.’

What you can do at home

Monitor your hardwood trees (like oaks, maples, beech and walnut), for the presence of larvae.

Spongy moth spend the winter in egg masses. Egg masses can be found on a variety of surfaces including trees, rocks, houses, boats, trailers, fences, picnic tables, and firewood.

Figure 2: Female spongy moth with egg mass

The eggs hatch in spring (April to mid-May) and young caterpillars begin feeding by cutting small holes in the surface of leaves. You can identify them by the five pairs of blue and six pairs of red spots along their backs. Feeding is normally completed by early to mid-July.


Help manage spongy moth by following these techniques:

April to August - Burlap Banding

Once Spongy Moth caterpillars grow to about an inch (2.5 cm) in length by mid-June, they will move down the trunk to seek shelter from predators and heat. Reduce the number of larvae on the trees in your yard by trapping them.

Figure 3: Burlap banded trees

 Step-by-Step Instructions

  1. Wrap and secure a piece of burlap cloth around the stem/trunk of your tree
  2. Tie twine or rope around the center or slightly below the center of the burlap
  3. Drape the burlap cloth over the twine or rope so there is an overhang where the caterpillars can crawl underneath to seek shelter during the day
  4. Check the trap by lifting the overhanging burlap cloth every afternoon and collect any hiding caterpillars
  5. Put them into a bucket of soapy water for 2-3 days to destroy them 

Late May to early June - BTK Application

You can apply a product that contains BTK (Bacillus Thuringiensis “kurstaki”) to foliage at the early stage of caterpillar development when caterpillars just begin feeding. This is usually around mid-May. The pesticide must be ingested by the caterpillar to be effective. 

For small trees and shrubs that you can reach, products like Safer® Brand Caterpillar Killer can be purchased at local garden supply stores.

June to July - Hand Pick Caterpillars

Handpicking caterpillars is still one of the most effective ways to help control Spongy Moth on small newly planted trees, shrubs, and plants. If possible, you can also gently shake the tree, so caterpillars fall from the leaves. Thoroughly inspect the remaining foliage, branches, and trunk for caterpillars, and using gloves, pick them off your tree. Fallen and collected caterpillars should be placed and left to soak in soapy water.

What to look for - The caterpillars of Spongy Moth are dark and hairy. They have five blue dot pairs and six red dot pairs on their back. They go through 4-5 "molting" events where they shed their skin and each time, they get bigger. 

July to August - Spongy Moth trap

Step-by-Step Instructions

  1. You can purchase the traps at various retail stores or online throughout your area
  2. Put the traps out when the moths are active after coming out of their pupa stage of growth. Only male moths are attracted to the traps.
  3. Homemade traps can be created with various designs found on websites. The traps have a bait inside their lid that smells like female Spongy Moth pheromone for attracting males.
  4. Once captured, put the moths in a container of soapy water and leave them for 2-3 days, then dispose of the contents.​

August to April - Egg Mass Removal

Survey your property for egg masses and scrape them off surfaces into soapy water to destroy them.

Step-by-Step Instructions

  1. Place your catchment container below the egg mass
  2. Use your scraper tool to remove the egg mass from the surface. Ensure that all eggs
  3. are scraped. Try not to leave any residual eggs in bark ridges or crevices.
  4. Empty the contents of your catchment container or bag into a bucket of soapy water
  5. Leave the eggs sitting in the bucket for 2-3 days, then dispose of the contents.

Egg masses can be located high up in trees. Care needs to be taken if trying to access anything aloft, especially if using ladders. Some private tree care companies can be hired to provide this service at heights.

Frequently Asked Questions

What kinds of trees are most affected by the Spongy Moth caterpillar?
Spongy Moth caterpillars prefer the leaves of deciduous hardwood trees like maple, elm and oak. It will also feed on apple, alder, birch, poplar and willow trees. As the caterpillar matures, and population levels increase, it will also begin to attack evergreens such as pine and spruce. Spongy Moth caterpillars don't appear to like ashes, sycamores, butternuts, black walnuts and dogwoods.
How much damage can Spongy Moth cause to trees?
Tree damage depends on the degree of infestation, past defoliations, the tree's vulnerability and the environment and can range from light to almost complete defoliation. If the tree has been weakened or stressed by other conditions, and attacked repeatedly in recent years, the defoliation can result in the death of the tree.
Does Spongy Moth have any natural enemies?

Yes. Predators include other insects like wasps, flies, beetles, ants and spiders as well as birds such as chickadees, blue jays, robins and nuthatches. Animals such as chipmunks, squirrels and raccoons will also prey on the caterpillar.

The wasp that targets the Spongy Moth is a parasite of the egg. It is now commonly found wherever Spongy Moth moths are and has become an important natural control.

Also, Spongy Moth is susceptible to several naturally occurring diseases caused by bacteria, fungi and a virus. The virus and bacteria escalate when populations peak. The Spongy Moth virus disease is often referred to as “wilt” because dead caterpillars hang in an inverted “V” from tree trunks or foliage.

These natural biological controls contribute the most to keeping levels within a normal range and tend to follow 2-3 years after the moth populations peak.

Is the City of Cambridge spraying for Spongy Moth?

Recent surveys of spongy moth activity in the City of Cambridge have shown a relatively low presence. Because of this, no aerial spray program to control the insect will be done. However, residents should contact our forestry department to report a city-owned tree affected by spongy moth – we will determine the appropriate course of action.

What can residents do?
Property owners are responsible for managing trees (and pests) on their property. You are encouraged to monitor trees on your property - look for egg masses in winter, caterpillars in spring, and moths in July and August - and take action to remove Spongy Moth as often as possible.
Should property owners consider a commercial insecticide to help control the Spongy Moth population?
During severe infestation an insecticide may be considered a viable option. Homeowners can consider consulting with, and hiring a licensed contractor to apply pesticide sprays or tree injections. Timing of the application and the treatment of the entire canopy is essential to the success of control. You should also be aware that pesticide applications do not produce an instant defense and will not completely eradicate the problem, but can be very effective in reducing the insect population when used appropriately.
Why are there still some egg masses on boulevard trees, after the City has been by?
Our arborists have worked to remove the egg masses from City trees to reduce the population. It is not possible to eliminate this pest completely as it is well established in our region.  Our overall objective is to reduce numbers. We continue to monitor numbers and will take further action if deemed necessary.
My family has been experiencing rashes that we think come from Spongy Moth caterpillars. What should we do about this?
The hairs of the Spongy Moth caterpillars contain histamine which some people are allergic to. Not everyone will have a reaction if coming in contact with the caterpillar, but it is possible and is a known adverse effect. If you are experiencing any sort of reaction, please contact your family care physician for medical advice.


Emerald Ash Borer (EAB)

What is an Emerald Ash Borer (EAB)?
The EAB is a species of beetle, which attacks and kills ash trees. Originally found in Asia, the EAB has killed millions of trees in North America.
Where are EAB infestations found in Cambridge?
This pest was originally detected in two woodlands on either side of Highway 401 at Homer Watson Boulevard within the cities of Cambridge and Kitchener. It is thought that this forest pest arrived at this location along the highway several years ago and since that time has become well established throughout Cambridge.
 How will Cambridge solve the EAB issue?

Out of about 55,000 street trees in the City of Cambridge, more than 4,000 are infested with EAB. Certified arborists inspect our ash trees and assign a rating based on several factors, including:

  • Infestation level
  • Structural condition

Using this rating system, we schedule tree removals in a priority sequence, beginning with the highest priority trees.

Learn more about the City's Emerald Ash Borer (EAB) Management Action Plan.
When will infected trees be removed?
The City of Cambridge Forestry department will continue to remove infested ash trees as needed.
Who can I contact for more information?
Contact the Service Cambridge Call Centre at 519-623-1340 for more information about EABs and our plan to solve this issue.