Spongy moth

The caterpillars tend to only eat leaves for a short period of time throughout June and July. Most trees will put out new leaves when the weather is favourable (with periodic rain).

While forested areas may be affected by spongy moth, trees in urban areas including street trees on local and regional roads and trees on private property are most at risk; soil compaction, air pollution and other pests and diseases make trees in urban areas more susceptible.

While most healthy trees can withstand several years of severe defoliation, trees that are already in poor health may have a harder time recovering. Additional stressors such as other pest/diseases or hot, dry weather may result in tree decline or mortality.

At high numbers, caterpillars can be a nuisance; caterpillar droppings and bits of foliage dropped by feeding caterpillars can create messes on decks and walkways near infested trees, on York Regional Forest trails and in local parks and greenspaces.

Although York Region experienced an infestation of spongy moth last year, trees across the Region showed resilience and most put out new leaves ending the summer with full canopies.

Did you know?

York Region was not the only area to experience an infestation of spongy moth last year. Many areas across southern and central Ontario were also affected.

Note: This map does not reflect defoliation in the Greater Toronto Area because of the no-fly zone issued for this area.
Credit: Ministry of Northern Development, Mines, Natural Resources and Forestry

Learn more:

• Watch Invasive Species Centre’s webinars - ​​​​Forests Under Attack: The History, Dispersal and Management of Gypsy Moth and​​​​​ LDD Moth: Taking Stock of Current Management Options in Ongoing Outbreaks
• Watch Toronto Region Conservation Authority's webinar - LDD Moth Ecology and Management Options

There are several pest management options you can consider to control the impact of spongy moth. Always wear gloves when handling caterpillars, egg masses and pupa to avoid an allergic reaction.

Control Options 

August to April

• Egg masses can be scraped off trees into a bucket of soapy water, stirred then left for a day or two before disposing of them
• Egg masses can be found in tree bark crevices or other out of the way places like garbage cans, firewood piles and children’s toys
• Leave burlap bands up until the end of August and then remove; moths may lay eggs under the burlap making them easier to find
• Burlap and twine/rope can be reused next year if spongy moth populations reach high numbers, or put it in the garbage so it doesn’t become litter

Watch the City of Markham video - Lymantria dispar dispar (LDD) in the City of Markham

April to June

• If trees are severely infested (many egg masses are visible), an insecticide may be a viable option
• Homeowners should contact a licensed tree care company to discuss the best options
• Some products have very tight timing windows for application to be successful and may require more than one treatment; if an opportunity to treat trees is missed this year, homeowners may want to reserve a spot the following spring

May to August

• To trap caterpillars (making them easier to collect), wrap a piece of burlap around the tree’s trunk at chest height, tie twine/rope around the middle or slightly below the centre of the burlap
• Drape the burlap over the twine/rope so there is an overhang where the caterpillars can crawl under to seek shelter during the day
• While burlap bands DO NOT stop spongy moth caterpillars from climbing trees and eating the leaves, they are a safe and effective collection method
• Leave burlap bands up until the end of August and then remove; moths may lay eggs under the burlap making them easier to find
• Burlap and twine/rope can be reused next year if spongy moth populations reach high numbers, or put it in the garbage so it doesn’t become litter

Watch the City of Markham video –  Lymantria dispar dispar (LDD) Burlap Banding Traps
Read the York Region Burlap Band Information Sheet – Protect Your Trees

June to July

• In the spring and into the summer, caterpillars can be handpicked
• By mid-June, caterpillars will grow to about 2.5 centimetres in length and begin moving down trees during the day to seek refuge from the mid-day sun and will climb back up at night to eat leaves
• Each afternoon, check burlap bands for caterpillars by lifting the overhanging burlap 
• Remove caterpillars and place in a bucket of soapy water, stir then dispose of them after a day or two
• In late June through to July, caterpillars will enter the pupa stage; remove pupa and place in a bucket of soapy water, stir then dispose of them after a day or two
• Always wear gloves when handling caterpillars, egg masses and pupa to avoid an allergic reaction
• Note: check your burlap bands daily to ensure birds or any other wildlife don’t get unintentionally caught. If you come across injured wildlife, contact your local Animal Control Services or Wildlife Rescue:​​​​​
  • Toronto Wildlife Centre
  • Shades of Hope
  • Procyon Wildlife

York Region and local cities and towns are focusing their efforts on high-risk and high-value street and park trees and implementing the following integrated pest management strategies as necessary:

• Egg mass scraping
• Treating high-risk newly-planted trees with ground-based treatment of Bacillus Thuringiensis Subspecies Kurstaki (Btk)
• Treating select high-value street trees with a biological insecticide called TreeAzin™

When used as directed TreeAzin™ and Btk pose minimal, if any, risk to people, pets, wildlife, soil and water.

Many local cities and towns are offering a variety of educational tools and resources including burlap band kits and demonstrations. Check your local city or town website for more information.

As a preventative measure and part of our ongoing practice, staff continue to monitor street, forest and park tree plots at greatest risk.

In July, the Region will conduct defoliation surveys on previously-surveyed plots to look at the actual defoliation levels (which the egg mass surveys in 2021 attempted to predict), and look for signs of the nucleopolyhedrosis virus (NPV). Actual defoliation versus predicted defoliation helps confirm the accuracy of the egg mass surveys and signs of NPV can be an indicator that the spongy moth population is declining.

In late fall/early winter, staff will be resurveying the plots for egg masses to help with 2023 spongy moth predictions.

Spongy Moth FAQs

Why is the Region using the term ‘spongy moth’? Isn’t it also known as Lymantria dispar dispar (LDD) and European gypsy moth?
While this pest may be referred to by different names, the Entomological Society of Canada (ESC) recently adopted the new common name of ‘spongy moth’ to replace Lymantria dispar dispar (LDD) and European gypsy moth.

Lymantria dispar dispar (LDD) was previously known as ‘gypsy moth’ (and more recently in media reports as ‘LDD moth’). The previous common name was removed from the list of accepted common names in 2021 for its use as a derogatory term for the Romani people.

The new common name was selected to acknowledge the spongy egg masses that the insect produces.

Are the web nests that I’m seeing in the trees made by spongy moth caterpillars? And are they harmful?
Spongy moth caterpillars don’t make web nests. There are several other types of caterpillars that make nests at different times throughout the growing season. If you’re concerned about other caterpillars affecting your tree(s) consider contacting a licensed tree care company to discuss the best options.

Does the spongy moth have any natural enemies?
Squirrels, chipmunks, raccoons, skunks, over 15 species of birds, and several native insects will all help reduce numbers, as will a naturally occurring fungus (Entomophaga maimaiga) and virus (nucleopolyhedrosis). The fungus and virus are harmless to people. These will all contribute to cause an eventual collapse in numbers if the population builds to high levels in a particular area. 

I heard that the cold temperatures we experienced this winter may have killed some of the spongy moth egg masses. Is that true?
Historical evidence suggests that during prolonged periods of extreme cold weather (i.e. temperatures that stay below -20 degrees Celsius for more than two days), exposed egg masses (like those laid on the outside of tree bark or other objects) may die. Egg masses laid at the base of a tree or under an object, however, will be insulated by the snow. We will only know if the extreme cold negatively impacted the egg masses if they don’t hatch this spring.  

Is this the last year of the spongy moth outbreak or will it happen again next year?
In 2021, York Region experienced a significant spongy moth outbreak which is part of a typical 7 to 10-year cycle with peak infestations lasting 1 to 3 years.

Based on spongy moth egg mass surveys conducted in fall 2021, it appears 2022 may be the start of a declining spongy moth population. While defoliation levels overall may be lower in 2022, trees are still at risk as spongy moth populations are predicted to reach high numbers in 2022 and heavy-to-severe defoliation is still anticipated in many parts of the Region.

To predict spongy moth populations for next year, egg mass surveys will be conducted in the fall of 2022. The number and size of egg masses in sample plots will give an indication of whether the population is increasing, decreasing or staying the same for the following spring/summer.

Resident SPONGY MOTH FAQs

What can residents do to protect the trees on their property?
Similar to other tree/forest pests (Emerald ash borer, Forest tent caterpillars, etc.), it is generally the responsibility of the tree owner to maintain the health of their trees and to seek control/removal of the undesirable tree pest if required. 

There are a number of ways homeowners can manage the impacts including treating trees with insecticide, hand picking caterpillars or removing egg masses and pupa. Always wear gloves when handling caterpillars, egg masses and pupa to avoid an allergic reaction.

Homeowners may also consider contacting a licensed tree care company to discuss best options for dealing with privately-owned trees including hiring a licensed contractor to apply pesticide sprays or tree injections. 

Why should I stir the egg masses and caterpillars when I put them in a bucket of soapy water?
To ensure egg masses and caterpillars are destroyed, it is important to make sure they are completely covered with soapy water. If the egg masses or caterpillars are not in contact with the soap, caterpillars may still hatch from egg masses and caterpillars will survive and make their way up a tree.

Can I apply sticky tape around the tree trunk to prevent caterpillars from climbing the tree?
This method is not recommended due to the potential for injury/death to unintended insects as well as small animals including mice or chipmunks getting stuck on the sticky tape. Burlap bands, when checked regularly, are a safer way to collect and dispose of spongy moth caterpillars that would otherwise be high up in the branches eating the leaves of the trees.

Where can I purchase burlap?
Burlap can be purchased at your local hardware store. You may also want to check with your city or town as many are providing burlap band kits and live demonstrations on how to properly install burlap bands.

Can I install a pheromone traps to control spongy moth on my property?
Pheromone traps available in Ontario are meant to be used to detect the presence of spongy moth or to monitor the spread of the spongy moth as it moves through an area. They are not technically calibrated or registered to be used as a method of controlling spongy moth populations specifically and may not be effective in reducing population numbers when spongy moth populations are high.

I notice that my tree is starting to lose leaves but water restrictions are currently in place where I live. Am I allowed to water it?
If trees have been defoliated, it is recommended that they be watered during hot, dry periods to help them recover and put out new leaves. If water restrictions are in place in your area, contact your city/town to find out if you can water your tree as each city/town has their own Outdoor Water-Use Bylaw.

My family has been experiencing rashes that we think come from spongy moth caterpillars. Are the caterpillars biting us? What should we do about this?
Spongy moth caterpillars do not bite or sting. The bite-like reaction or rash being experienced by some is most likely the result of the little hairs on the spongy moth caterpillar coming into contact with the skin. You may not even notice the caterpillar landing on you but the little hairs can fly through the air and land on your clothes or your skin. Histamine found in the caterpillar’s hair can cause red, itchy bumps to form.

While the rash is not contagious, it can be quite uncomfortable. In severe cases it may last for up to a week or longer, depending on your sensitivity. Wearing a hat, gloves, long sleeves and long pants can help protect your skin from coming into contact with the hairs. Consider washing clothes worn outside each day as the hairs might still be on your clothes the next day. When handling caterpillars, egg masses and pupa always wear gloves to avoid an allergic reaction.

Who offers spongy moth services in York Region?
There are many licensed tree care companies that service York Region who may provide spongy moth control services. Most companies will provide a free site visit and estimate. It is recommended that you get more than one quote and request proof of insurance before work begins. You may also want to inquire if arborists are certified by the International Society of Arboriculture. This professional certification program ensures members have specific knowledge and competencies and requires continued learning in order to maintain certification. 

York Region Spongy moth FAQs

Will trees in the York Regional Forest be affected by spongy moth?
Based on spongy moth egg mass surveys conducted in fall 2021, it appears 2022 may be the start of a declining spongy moth population. While defoliation levels overall may be lower in 2022, trees in the York Regional Forest are still at risk as spongy moth populations are predicted to reach high numbers in 2022 and heavy-to-severe defoliation is still anticipated in a number of Forest tracts. In areas with a lot of spongy moth caterpillars, visitors may be able to hear the caterpillars eating the leaves and their droppings and bits of leaves may be visible on the trails.

I noticed some street trees in my area have a lot of spongy moth egg masses/caterpillars. Is there a number I can call to report it?
If you suspect an infestation of spongy moth egg masses/caterpillars on urban street trees found on a regional road, please report it through Access York by email at @email or by telephone at 1-877-464-9675. Every effort by York Region staff will be made to assess the urban street tree/area of concern.

If warranted, staff may remove egg masses from select smaller high-risk street trees and/or consider applying treatment on high-value street trees. With such a large inventory of urban street trees, it is not feasible to assess and address every tree. Priority will be given to smaller high-risk, and larger high-value urban street trees that have already been identified by staff.

If the trees are on a local road (your neighbourhood roads), please contact your local city or town.

What does the Region consider to be a high-value street tree versus a smaller high-risk street tree?
Large, esthetically pleasing and in some cases really old trees, are considered high-value. These trees warrant insecticide treatment because of their significance on the landscape. Younger trees identified as having the most egg masses per individual tree, are classified as smaller high-risk trees. Egg mass scraping is more easily done on these trees.

Why are there still some egg masses on street trees, after the Region has treated them?
Regional staff are removing egg masses from select smaller high-risk street trees in an attempt to reduce the overall defoliation of those trees. It is not feasible to remove all egg masses from all trees and any remaining egg masses on trees that staff have visited mean they were not safely within reach of the equipment used to remove the egg masses. 

If the Region treats street trees on Regional roads, who treats street trees on local roads and in local parks?
York Region treats street trees on regional roads – main roadways that connect our nine local cities and towns to one another (i.e. Yonge Street, Dufferin Street, Highway 7 and Major Mackenzie). Your city or town treats street trees on local roads (your neighbourhood roads) and in local parks.

What is the difference between a Regional road and a local road?
Regional roads are typically main arterial roadways that connect our nine local municipalities to one another. They are operated and maintained by The Regional Municipality of York. Each is identified by a numbered Regional road sign. Local roads are operated and maintained by local cities and towns.

Will trees in the York Regional Forest be treated?
The Region will not be implementing integrated pest management strategies on trees in the York Regional Forest because those trees are at lower risk. Natural ecosystems, like those found in the York Regional Forest are often more resilient to pests and diseases than urban street trees.

SPONGY MOTH Treatment FAQs

What is the difference between a pesticide, an insecticide and a herbicide?
Pesticides are chemicals used to kill things like fungus, bacteria, insects, plant diseases, snails, slugs and weeds. Insecticides are a type of pesticide used specifically to target and kill insects. Herbicides are a type of pesticide used to control unwanted plants.

What is TreeAzin™ and Btk?
TreeAzin™ is a botanical injectable pesticide made from the seeds of a Neem tree. It provides a treated tree with protection from spongy moth feeding for one season. When a caterpillar eats the leaves of a treated tree, the pesticide kills the insect by preventing it from growing any larger. This limits the amount of defoliation to the tree. This treatment method is being applied to only a few high-value street trees where Btk ground sprays and egg mass scraping would not be feasible.

Btk ground sprays contain an active ingredient called Bacillus thuringiensis subspecies kurstaki (Btk). This is a naturally occurring bacteria found in soil that can be sprayed onto the foliage of individual trees. The best time to apply Btk is mid to late May when the caterpillars are small (less than 2.5 centimetres). As the caterpillars grow, they need to ingest greater amounts of Btk, and the larger caterpillars won’t ingest enough Btk for it to be effective.

Will the Region conduct an aerial spray this year to manage spongy moth?
The Region evaluated the possibility of an aerial spray for select parts of the York Regional Forest. After observing the level of defoliation and natural resiliency of the trees during the summer of 2021, Regional Council in fall 2021, determined that an aerial spray is not warranted and that focus should remain on individual high-risk and high-value street trees.

What are the issues associated with aerial sprays?
Aerial sprays do not reduce spongy moth populations over the landscape in the long term, especially when their presence is widespread and infestation levels are at their peak. They are also non-selective and can impact non-target caterpillars, who are an important source of food for many birds, pollinators and other wildlife.

Since aerial sprays require two applications within a very narrow time frame which need to occur right after the caterpillars emerge and requires specific weather conditions, they are logistically complex. Due to the negative public perception associated with aerial sprays of pesticides, some homeowners/landowners and environmental groups may oppose aerial spraying of Btk or the use of pesticides in general.