LDD Moth (European Gypsy Moth)*

*PLEASE NOTE: In its ongoing effort to lead an inclusive organization, Toronto and Region Conservation Authority (TRCA) is transitioning away from the use of “gypsy moth” and will be using the term “LDD moth” moving forward.

TRCA Actions

June 2021: The LDD moth infestation is at its peak for 2021 and TRCA is starting to observe evidence of the naturally occurring NPV virus in caterpillars. This virus will kill LDD moth caterpillars and cause them to hang in an upside down V. Caterpillars that are not infected by the virus or killed by other natural factors will start to pupate over the next few weeks.

For more information on the LDD moth, please see below and view our webinar


The LDD moth (Lymantria dispar dispar) is a non-native moth species that can cause defoliation of trees in Ontario and Eastern North America.

The caterpillars will eat the leaves of more than 400 species of plants. They prefer oak, but will also eat other hardwood trees such as sugar maple, spruce, elm, birch and poplar.

They also feed on garden shrubs, flowering plants, and coniferous trees.

LDD moth caterpillar
LDD moth adult male
LDD moth adult female

IMAGES: LDD moth larval caterpillar stage; adult male (Photo by Ryan Hodnett – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=50965794); and adult female (Photo courtesy of City of London)

LDD moth outbreaks in Ontario are cyclical, occurring every five to ten years.

During severe population outbreaks, caterpillars can devastate trees and forests. A single LDD moth caterpillar can consume one square meter of leaves in a season.

Several years of defoliation can cause tree mortality, especially when it occurs alongside other stressors such as droughts, forest tent caterpillar (Malacosoma disstria) outbreaks, and fungal pathogens, although most hardwood trees are able to survive up to three years of defoliation.

LDD moths do not typically eat the leaves (or needles) of coniferous trees such as white spruce unless they have run out of other leaves to eat. Unfortunately, coniferous trees may not survive a single bad year of LDD moth infestation.

In addition to ecological impacts, such as compromised health of trees and changes to forest composition over time, there are also economic and social impacts of an outbreak, including the temporary loss of beautiful forest canopies and the cost of removing and replacing dead trees from areas and parks. Some people even have allergies to LDD moth caterpillar hair.

TRCA is taking an Integrated Pest Management approach. This means that we are monitoring certain areas and evaluating management options, which may involve using a combination of techniques.

Given that LDD moths are behaving like a native pest, and many other invasive species require management, TRCA is unlikely to undertake widespread management.

Instead, management actions will focus on the protection of important individual trees or groups of trees (such as shade trees within a manicured area of a conservation park).

TRCA will support its neighbours through information and education about management techniques, as described below. Please note that TRCA will not visit private properties to assess or treat pest infestations. Property owners should contact tree service companies for assessment and other control options.

If you have a property at least 2 acres in size, you may qualify for subsidized tree planting under TRCA’s Private Land Planting Program, or if you have a forest at least 4 hectares in size, you may qualify for Forestry and MFTIP planning services. If you have a rural property you may qualify for the Rural Clean Water Program.

Contact us for more information: trees@trca.ca.

  • Learn to identify the LDD moth during its various life stages (see next section).
  • Keep your trees healthy to minimize the impact of LDD moth defoliation stress by ensuring your trees get enough water, and for individual trees or a woodlot conduct good forestry practices minimizing detriments to other forest values such as impacts to root zones and overall water quality.
  • Report sightings to the toll-free Invading Species Hotline at 1-800-563-7711 or email info@invadingspecies.com. You can also submit information about your sighting at EDDMaps.org
  • Practice the management techniques below.


Activity Timing Notes
Hand Picking Caterpillars May to July Scrape off caterpillars into water/soap mixture, leave for a few days and then dispose in the garbage. Do not scrape caterpillars onto the ground. NOTE: Wear gloves since caterpillar hairs can cause skin irritation or allergies.
Burlap Banding June to August Place burlap band around truck where caterpillars will hide during the heat of the day. Check bands regularly and scrape caterpillars into a container with soapy water for a few days and dispose of in garbage. NOTE: Wear gloves since caterpillar hairs can cause skin irritation or allergies.

Pheromone Traps July to August Pheromone traps are intended to attract and trap male adult LDD moths, to prevent them from mating with females. Generally, this is used as a monitoring technique but may reduce egg mass loading in small areas. Traps should be disposed of in the garbage.
Scraping Egg Masses August to early May Scrape off egg masses into soapy water, leave for a few days and dispose of in the garbage. Do not scrape egg masses onto the ground, this does not kill the eggs and may actually improve survival. NOTE: Wear gloves since caterpillar hairs can cause skin irritation or allergies.

*These techniques are for protecting individual trees, and are not intended for large-scale management.

1. How to Identify the LDD Moth

  • The LDD moth has four life stages: egg, caterpillar, pupa, and moth.
  • Caterpillars start off very small (about 2mm) and molt three to four times, growing larger each time. By the time they reach their last molt, caterpillars can be 5-6cm long. They are dark and hairy, with five blue and red dot pairs on the back.
  • As adults, female moths are white with dark markings and cannot fly.
  • Adult male moths are brown with dark markings and large feathery antennae, and can fly.
  • Egg masses (shown below) are tan in colour, between the size of a dime and toonie and can be found on tree trunks, under bark, the outsides of buildings and cars, on patio furniture, on tents and trailers, etc.
LDD moth egg mass on tree trunk
LDD moth egg mass on tree trunk
LDD moth egg masses on tree trunk

IMAGES: LDD moth egg masses (TRCA photos)

2. LDD Moth Life Cycle

  • Egg masses hatch into caterpillars in the spring just as tree leaves begin to flush out. The caterpillars are tiny at this time and may not even be noticed. They can be carried by the wind for distances of up to 1km.
  • Caterpillars are most active in May and June and their appetite grows as they get larger. Caterpillars typically eat at night and seek shelter during the heat of the day.
  • Caterpillars become pupae in late June-early July and remain in this stage for 1-2 weeks.
  • Adult moths emerge from the end of June through to August and live for about 2 weeks. They exist solely to reproduce; they do not eat. Only male moths can fly and during this time they pursue females by following the pheromone scent females produce.
  • Females produce only one egg mass in their lifetime which can contain 100-1,000 eggs.
  • Egg masses persist through the winter and ones that are buried by snow typically have higher survival as the snow protects them from temperature extremes.

Select life cycle image below to view a full-sized version of the chart.

LDD Moth Life Cycle

3. What Makes This Invasive Species More Like a Native Pest?

The LDD moth arrived in North America as a result of a misguided attempt to create a domestic silk industry. Its presence was met with alarm as the impact of defoliation became apparent.

Recent evidence, however, indicates that LDD moths are behaving more like a native pest than an invasive species. This is due, in part, to the presence of several natural factors that help to regulate the population:

  • The fungus Entomophaga maimaiga overwinters in soil and infects LDD moths, resulting in their death. It needs cool, wet weather to persist and be effective.
  • The nuclear polyhedrosis virus (NPV) infects caterpillars, causing them to climb to the top of the tree and die. The dead larvae become liquified, helping the virus to spread and infect other caterpillars. (It can also be spread through the feces of birds that eat dead or dying caterpillars.) The effectiveness of the virus is dependent on high caterpillar density — the more caterpillars there are per tree, the more likely that NPV can spread and effectively control populations.
  • Prolonged extreme cold (below negative 26 degrees Celsius) coupled with a lack of snow can kill LDD moth eggs.
  • Natural predators including other insects, spiders, and several birds will eat LDD moths in their various life stages — although this factor alone is unlikely to have significant population effects.
  • Parasitoids (species that use others as hosts for their young) kill LDD moths by feeding on their tissue. These species may play an important role in population control; however, this is not yet well understood.
  • Host tree natural defences: as host trees are eaten by LDD moths, they respond by growing tougher, less nutritious leaves making it more difficult for caterpillars to be successful.
  • Competition between LDD moths and ultimately starvation due to a lack of food will cause a collapse of LDD moth populations, which is reflected by their typical cyclical outbreaks.

Lymantria dispar dispar (LDD moth or European gypsy moth) is a non-native insect that defoliates trees in North America. Outbreaks occur every five to 10 years.

Because the LDD moth behaves like a native pest, TRCA is not overly concerned about its long-term effects on our forests. However, the 2021 infestation is predicted to be moderate to severe. Therefore, TRCA is proceeding with the aerial treatment of areas within some Conservation Parks to mitigate damage.

What is Integrated Pest Management (IPM)?
TRCA is currently taking an Integrated Pest Management (IPM) approach to the LDD moth outbreak. IPM focuses on the long-term prevention and mitigation of pests or their damage through techniques such as monitoring, biological control, and manual control.

A major component of this program consists of egg mass surveys in the fall and winter to predict defoliation levels for the following year. Following that, prescription and implementation of various control strategies can be undertaken.

Given that the LDD moth is behaving like a native pest, and that many other invasive species also require management, TRCA will not undertake widespread management. Instead, management actions will focus on the protection of high public use areas.

TRCA has determined that an aerial spray of a biological insecticide is prudent for certain areas of our jurisdiction.

Why is the TRCA planning an aerial spray?
TRCA’s monitoring indicates that 2021 will be a moderate to severe year for LDD moth infestation. While we are not overly concerned about the long-term effect this may have on our forests, the infestation is likely to impact significant trees in high public use areas within TRCA’s Conservation Parks.

To address this concern, TRCA will undertake the aerial application of Btk, a biological insecticide, in specific areas of several Conservation Parks:

Aerial spraying has proven in the past to be very effective in lowering LDD moth populations. Although the aerial spray will not eradicate all traces of the insect, it will lower populations to help mitigate tree damage.

Two applications of Btk are required for maximum effectiveness.

Which specific areas will be sprayed?
Please refer to the figures below.

What type of pesticide is being used?
The TRCA will be using a product that contains Bacillus thuringiensis subspecies kurstaki (Btk). The product is registered under the trade name Foray® 48B.

Btk is a naturally occurring bacteria found in soil. Btk is not a chemical. It is a rod-shaped bacterium that occurs naturally on dead or decaying matter in the soil. It is grown from soil bacteria that occur naturally worldwide.

When Btk is ingested by a susceptible caterpillar, the highly alkaline environment of the caterpillar’s gut triggers the Btk bacterium to release a crystalline protein called an “endotoxin” that poisons the insect’s digestive system. The caterpillars must ingest the Btk bacterium to be affected.

Btk was successfully used by the City of Toronto in 2007, 2008, 2013, and 2017 to control LDD moth populations. The cities of Mississauga, Oakville and Hamilton have also completed similar spray programs in the past.

What organisms does Btk pesticide affect?
Btk only works against organisms that go from egg to larvae to pupae to moth (Lepidopterans or caterpillars).

Btk does not affect adult moths and butterflies, including the Monarch butterfly, as these are not in the caterpillar stage and feeding on plant material at this time of the year.

Btk does not affect other insects, honeybees, fish, birds, or mammals.

How does Btk work?
Btk produces a protein that is toxic only to the caterpillars (larvae) of specific insect species.

When ingested by susceptible insects, the toxic protein molecules break down the walls of the insect’s stomach causing the insect to stop feeding. The insect usually dies within two to five days.

For Btk toxins to be activated, the alkaline conditions that exist only in certain insects’ digestive systems must be present. The alkaline conditions that activate Btk toxins are not present in the stomachs of humans and animals, rendering the insecticide non-toxic to them.

Btk has been used in many countries without health impacts to individuals on medications or other vulnerable people.

When should Btk be used?
The best time to apply Btk is early to late May, when the caterpillars are small. Btk is less effective in older, more mature caterpillars, and is highly ineffective during the non-feeding life stages of the LDD moth: eggs, pupa, and adult moths.

What is the formulation of the Btk product?
The registered name of the pesticide that will be used by TRCA is Foray® 48B Biological Insecticide Aqueous Suspension. It is registered under the Pest Control Products Act (PCP # 24977).

It consists of 3% Btk bacteria, 75% water and 22% food grade inerts. The term “food grade inerts” refers to a special blend of additives that give the formulation protection against ultraviolet light and help make it stick to foliage. Food grade inerts do not pose any health risks.

Btk remains effective for approximately one to four days before it breaks down in the presence of sunlight.

What is the concentration of Btk?
A small amount of liquid covers a large area: four litres will cover one hectare (2.5 acres). Comprehensive spray drift modelling has been done to ensure accurate and effective application.

Who regulates Btk use in Canada?
Btk has been approved by the Pest Management Regulatory Agency, an agency of Health Canada, for aerial use.

Is Btk safe?
Btk is an effective pesticide that has been shown to successfully manage many lepidopteran species such as the LDD moth. It has been extensively studied by Health Canada and the US Environmental Protection Agency (EPA). Research shows that Btk poses minimal risk to human health when used as directed.

Btk is approved by Health Canada for aerial use over urban areas. It has been used by many countries over the last 30 years, including Canada and the United States. The City of Toronto has used Btk in multiple aerial spray programs in the past 10 years. Its use did not result in any reported health impacts to the general population.

The public is unlikely to experience any symptoms and no special precautions are necessary.

Btk aerial spraying is also not expected to have adverse effects on vulnerable populations including children with asthma, people with weakened immune systems, pregnant women, or the elderly. However, there may infrequently be some residents who are more sensitive and who may experience skin, eye, or respiratory irritation.

In addition to the Btk active ingredient, other ingredients called formulants have also been studied broadly and do not have any significant health risks. Formulants normally include water and other ingredients to make the product stick to leaves and needles of trees.

While the aerial spray will not eradicate the LDD moth populations currently present, it will reduce populations to more manageable levels to protect tree canopies.

Another subspecies of Bacillus thuringeiensis bacterium, called Bti, has been used to control mosquitos in surface water in the GTA for over a decade, as part of the effort to protect against West Nile Virus.

Aerial application of Btk has not been shown to have any negative environmental effects. Once applied, Btk biodegrades quickly, (in approximately one to four days), through exposure to sunlight and micro-organisms.

What personal precautions can be taken in preparation for aerial spraying?
Members of the public are unlikely to experience any health effects, and no special precautions are necessary or required.

Individuals who have concerns should take reasonable precautions to avoid exposure during an application period of the program. While no special precautions need to be taken, the following measures may be considered by residents living in treatment areas (Please note, however, that no residential properties will be treated):

  • Whenever possible, remain indoors for 30 minutes after spraying to allow for the droplets to deposit onto the tree leaves.
  • Bring laundry, toys and pets indoors before spraying begins.
  • Practice good personal and food hygiene (e.g., hand washing after outdoor activities, especially gardening, leaving outdoor shoes at the door, washing all fruits and vegetables before eating or cooking).
  • Cover lawn furniture, outdoor tables, pools, BBQs, play equipment, and sandboxes and/or rinse them off with water after spraying is finished.
  • Minimize opening and closing windows and doors during the spraying.
  • Shut off the heating/cooling vents or select the recirculate setting.
  • Contact your family physician if you are concerned that a personal medical condition may be aggravated by the spraying.

Does Btk spraying pose a risk to residents who might have sensitivities?
Members of the public are unlikely to experience any symptoms and no special precautions are necessary or required.

However, there may infrequently be some residents who are more sensitive and may experience skin, eye, or respiratory irritation. Btk aerial spraying is not expected to have adverse effects on vulnerable populations including children with asthma, people with weakened immune systems, pregnant women, or the elderly.

What should I do if I experience an adverse reaction?
If you experience an adverse reaction or worsening medical condition, speak to your physician or, in an emergency, call 911.

Can the LDD moth affect my health directly?
Extreme LDD moth outbreaks have been associated with skin rashes and upper respiratory tract irritation in some people exposed to airborne LDD hairs, silken threads, or shed skins.

There is a potential for some people to develop minor skin irritations or rashes when they come in contact with these insects. If this is a concern, it is recommended that you try and avoid contact whenever possible.

Is Btk safe for animals?
According to Health Canada, Btk is only effective during the caterpillar (larval) stage of the LDD moth life cycle. Btk does not affect adult moths and butterflies, including the Monarch butterfly, as these are not in the caterpillar stage at the time of the spray.

Btk does not affect other insects, honeybees, fish, birds, or mammals. There is no impact on animals or pets if they are exposed to or ingest Btk.

Where does Btk go in the environment?
Research shows that Btk used in aerial spray programs has not been found to have any negative environmental effects.

Once applied, Btk biodegrades quickly, in approximately one to four days, through exposure to sunlight and micro-organisms.There are no groundwater contamination concerns, as Btk does not travel through the soil beyond 25 cm.

How long does Btk remain effective?
Btk is applied to leaves when caterpillars are feeding. It breaks down quickly (in approximately one to four days) when exposed to sunlight and micro-organisms.

Is there a certain season or window of time the spray has to happen within?
The best time to first apply Btk is mid-May, when caterpillars are small, hungry, and feeding.

The first spray window is set for May 10 to 15, 2021. The follow-up treatment will occur five to seven days after that.

On the day of the sprays, the spraying will begin the very early morning hours and should be complete by approximately 9:30 a.m.

Applications can occur any day of the week, but will not occur on weekends.

The Btk application is weather-dependent. Ideal application conditions consist of:

  • Calm winds (1-16 km/h)
  • High humidity (40% or greater)
  • Temperatures between 2 and 25 degrees Celsius
  • No precipitation within the spray window, and ideally not for 24 to 48 hours after application

What type of aircraft will conduct the spray?
For this program, a single-engine aircraft with spray systems will fly approximately 30 metres above the treetops.

Why are only certain areas of TRCA’s jurisdiction getting sprayed?
TRCA undertook LDD moth egg mass monitoring in late fall/winter 2020, which determined that infestations are expected to be moderate to severe in 2021.

Based on this data, TRCA identified high public use areas within several of our Conservation Parks that are vulnerable to infestation.

TRCA is not spraying large areas of our forests because the LDD moth behaves like a native pest and forests are likely to recover after the infestation.

Furthermore, since Btk affects all lepidoptera species, and because caterpillars form an essential part of the natural food web and are especially important to migrating and nesting birds, TRCA is taking a conservative approach to Btk application.

How will I know the spray is happening? What happens if the spray is cancelled?
TRCA will post signs at treatment locations 24 hours before each treatment, and will provide up-to-date information both on this webpage and through Facebook and Twitter.

Bad weather or wind may cause the aerial spray to be postponed with little advance notice. The spray may be rescheduled or cancelled up to 24 hours in advance without public notification if the weather conditions change.

If the weather doesn’t co-operate and spraying can’t be done, what are TRCA’s next steps?
TRCA will continue to monitor pest population levels and consider appropriate treatment methods.

How is TRCA going to measure the success of the spray program?
Success will be measured by evaluating tree health through the months following the spray: are the trees green and covered with leaves, or are they completely defoliated?

As well, egg mass counts will be conducted in the late fall/winter.

Will spraying become an annual occurrence?
While insect infestations are notoriously difficult to predict, TRCA and other experts believe we are at the peak of the LDD moth cycle, and that the population will significantly decrease after this summer.

It is nearly impossible to determine if population levels of the LDD moth will require an aerial spray a year in advance. Decisions regarding whether to treat with an aerial spray will be taken after extensive egg mass surveying has been completed to determine if treatment is warranted or not.

What measures can I take to help keep the LDD moth population in check on my property?
Residents can help by:

  • Removing egg masses from trees and other hard surfaces. Soak them in soapy water for 48 hours and put them in the garbage.
  • Installing burlap skirts around tree trunks at beginning of June. Caterpillars will find shelter under the burlap, making it easy for residents to collect and dispose of them in the garbage.
  • Destroying pupae/cocoons.
  • Consulting with a private arborist when larger trees require attention for control of the LDD moth.

Though effective, these control options are time-sensitive: they must be implemented at the appropriate time to be effective. TRCA recommends the following timing:

  • September to beginning of May: Scrape LDD moth egg masses from trees and other hard surfaces, leaves, tree trunks, and branches. Soak them in soapy water for 48 hours to destroy them.
  • May to mid-August: Burlapping — install burlap wraps around tree trunks and then collect and destroy the caterpillars, pupae, adults, and egg masses.
  • End of June to mid-August: Collect, crush, or otherwise destroy pupae/cocoons when you see them.
  • Beginning of May to mid-June: Consider chemical treatments such as Btk-based products or TreeAzin; be aware, however, that the effectiveness of these treatments is extremely time-sensitive.

It is highly recommended that you consult with a private arborist no later than the end of April if you are looking at having your trees treated/sprayed, to properly schedule the work. Once the caterpillars grow too large (in approximately mid-June), pesticide treatments are no longer effective at controlling the LDD moth.

Some private arborists will conduct egg mass removal for your trees during the winter months.

Btk Treatment Areas on TRCA Properties

The maps below show the areas where TRCA will be conducting aerial application of Btk at its Conservation Parks. Select each thumbnail image to view a full-sized map.


View Our Webinar

LDD Moth (Gypsy Moth) Management: Protecting Our Forests

TRCA is pleased to provide, in partnership with Credit Valley Conservation (CVC), an information webinar on the LDD moth. We discuss the LDD moth life cycle, how to identify them, and what actions you can take to minimize their impact to trees. TRCA and CVC experts also answer questions from participants.

Contact Us

For more information on TRCA’s LDD Moth Strategic Approach, please contact:
Karen McDonald
Senior Manager, Restoration and Resource Management