Property, Gardens & Trees

Gypsy Moth

The City of Hamilton is not currently spraying for Gypsy Moths.


The European Gypsy Moth (Lymantria dispar dispar) is an invasive forest pest that was introduced accidentally in the United States in 1869. Since then, the Gypsy Moth has expanded its range over much of the eastern United States and Canada. It was first detected in Ontario in 1969 and has quickly spread across southern Ontario over the next decade. It is now well established throughout southern Ontario and as far north as Sault Ste. Marie.

How we are controlling Gypsy Moth

Gypsy Moth surveying has been underway since the winter of 2016 with the completion of egg mass surveys. An increase in egg masses suggests a coming season of increased pest activity. The monitoring initiated in late 2018 identified approximately 580 hectares that have exceeded an action threshold of 2,500 egg masses per hectare, and require treatment.

Marking trees

The City of Hamilton has marked trees that are monitored as part of the Gypsy Moth aerial spray program. These trees have a yellow spray painted dot. Please do not disturb these trees. The data being collected is very important for determining when the aerial spray program will be most successful at targeting Gypsy Moths.

Tree marked for the Gyspy Moth Aerial Spray Program

Gypsy Moth Treatment Area

The 2019 Spray Program took place between May 1 to June 30, 2019. To find out if you live in the treatment area, enter an address or intersection into the search box. If your search result appears in the pink highlighted boundary, you are located in the aerial spray zone.

Once the spray program has been completed this year, the Forestry Section will be conducting follow up surveys of the spray area, as well as areas outside of the spray area to verify that the gypsy moth population has decreased below threshold levels. If it has been determined that action thresholds have been reached in other areas, the Forestry Section will address it the following year.

Find more Gypsy Moth data in our Open Data Portal

Gypsy moth larvae or caterpillars will feed on tree leaves. If the larvae population is high, they can defoliate whole trees and forests in a short amount of time. Gypsy moth prefer oak trees, but will feed on a variety of hardwood tree species. Under normal circumstances, defoliation caused by gypsy moth 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 like Spring or Fall Cankerworm.

Bacillus thuringiensis ‘kurstaki’ (Btk) is a soil-borne bacteria that is applied to the leaves of affected trees while caterpillars are in their early instar stage (immature). Once ingested, the bacterium disrupts the caterpillars’ digestive system with cessation of eating within 24-48 hours. Within days, caterpillars that have ingested Btk will succumb to its effects. Btk has very low residual qualities in the natural environment. Sunlight and fungi deteriorate the bio-pesticide within 1 to 4 days. Because Btk requires an alkaline environment in the gut in order to be effective, it does not have any detrimental effects to humans, birds, or bees. Btk will affect other caterpillar species (known as non-target species). Due to its low residual and the narrow spray window due to larval development, the non-target impact is expected to be low. Conservative and measured application will be undertaken with the goal of reducing the population below the 2,500 egg masses per hectare. This program is not intended to eradicate the pest entirely.

Members of the public are unlikely to experience any symptoms if inadvertently exposed to Btk spray, and no special precautions are necessary or required. However, individuals who have concerns should take reasonable precautions to avoid exposure during a spray program in the same way they would avoid pollen or other airborne materials during days when air quality advisories are issued. They can also reduce exposure by staying indoors with windows and doors shut during the spray period if spraying is taking place in their area, although this is not required by health officials. (Health Canada, 2009)

Close up of Gypsy Moth Larva

Figure 1: Late instar gypsy moth larva

Close up of 3 Gypsy Moths

Figure 2: Female gypsy moths laying eggs

Gypsy moths spend the winter as partially developed larvae in eggs. The eggs hatch in the spring and the young larvae begin feeding by cutting small holes in the surface of leaves. As the larvae develop, they feed on the edge of leaves. Larvae have five pairs of blue and six pairs of red spots along their backs. Feeding is normally completed by early to mid-July.

Pupation occurs in a cocoon which can be found on a variety of surfaces including trees, rocks, houses, boats, trailers, fences, picnic tables, and firewood. In 13 to 17 days, the moths emerge. Both sexes have wings, but only the males can fly. The male moth is dark brown to beige, medium-sized, and is a very erratic flyer. The female is mostly white and has a wingspan between 60 to 70 mm. The female lays eggs in masses of 100 to 1000 on tree trunks, branches, houses, fences, etc. as well as under rocks and forest floor debris. The eggs are covered with fine brown hairs from the female’s abdomen. The egg masses will remain all winter and caterpillars will hatch in the spring, from late April to mid-May.

Homeowners are encouraged to monitor their hardwood trees like oaks, maples, beech and walnut for the presence of Gypsy Moth larvae. You can help manage Gypsy Moths by follow these techniques:

May to July: Hand Pick Caterpillars

Handpicking caterpillars is still one of the most effective ways to help control Gypsy moths 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.

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. Residents should have their trees sprayed with BTK by a qualified pesticide applicator if choosing this method.  

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

May to September: Burlap Banding 

Once European Gypsy 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.

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 a few days to destroy them
July to August: Gypsy 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 gypsy moth pheromone for attracting males.

August to May: 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 a day or two, 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.