An invasive forest defoliating insect found in Ontario that is now naturalized. Recent observations and surveys in the Ottawa area indicate its populations are increasing. The City of Ottawa is carefully monitoring the situation but does expect some defoliation to occur within the outbreak areas. The outbreak is expected to last two to three years.
Characteristics and Life Cycle
The European Gypsy moth is an invasive insect native to Europe. It is currently established in much of eastern Canada. The caterpillar stage of this insect feeds on the leaves and foliage of a large number of hardwood and softwood trees and can feed on over 300 plant species including landscape and garden plants.
Oak (Quercus) is the preferred species of the Gypsy moth with other hosts ranging from birch (Betula) and aspen (Populus), to various hardwoods such as sugar maple (Acer saccharum), American beech (Fagus grandifolia) and softwoods such as eastern white pine (Pinus strobus) and Colorado blue spruce (Picea pungens).
The Gypsy moth:
- Overwinters in the egg stage often on the bark of trees.
- In spring, eggs hatch and larvae ascend the trees to feed on the new foliage.
- Feeding occurs during the day, but as the caterpillars mature feeding occurs mainly at night — often this can delay the detection of infestations.
- Mature larvae are 50 mm long, dark coloured, hairy, with a double row of five pairs blue spots, followed by a double row of six pairs red spots, down the back.
- Feeding is completed in July-August.
- Male moths are light brown and slender-bodied, while females are white and heavy-bodied.
Tree impacts (signs/symptoms)
- Gypsy moth outbreaks can occur every seven to ten years.
- Larvae chew holes in leaves or devour entire leaves.
- In late July, spongy egg masses can be observed on the trunks and branches of infected trees and on items such as outdoor equipment, trailers and vehicles.
- During severe outbreaks, trees and shrubs are completely defoliated over large areas; despite the trees’ ability to produce a new crop of leaves over the summer, the damage causes significant growth loss.
- Understory shrubs and plants may also be affected.
What is the City doing about it?
The City of Ottawa is conducting Gypsy moth surveys which started in February 2021 throughout the urban and rural area to determine the extent of the outbreak. We have communicated with other partners such as the Ontario Ministry of Natural Resources and Forestry and they report to be monitoring the issue with increased populations of this insect in other areas of the province. City staff continue to monitor this issue and will communicate to residents about gypsy moth status in Ottawa and about best practices for residents to consider for control.
What might residents notice?
Residents may see large groups of caterpillars on tree trunks and branches and some loss of leaves (defoliation) on trees this spring as a result of this insect. Healthy trees are able to sustain loss of leaves and some trees will produce a second flush of leaves in the same season following leaf loss. It is only repeated years of caterpillar feeding that cause concern with tree health.
What residents can do?
On their properties, residents can consider the following to reduce tree damage:
- During spring and summer, inspect outdoor equipment, trailers, vehicles and firewood on a regular basis for egg masses and caterpillars.
- In spring, remove egg masses or larvae by scraping. Then destroy them immediately by crushing the eggs or by submerging the eggs into a bucket filled with water and household bleach or soap for at least two days. After two days, discard the solution and egg mixture.
- Between May and early June, Btk (Bacillus thuringiensis kurstaki) can be purchased at a local hardware store and applied. Always consult with knowledgeable professionals about pesticide use.
- In June and July, burlap can be attached to the trunk of trees using a string in a band around the trunk and folded in half. Often caterpillars will congregate in the burlap and this can be disposed of daily in compost etc. Caution: the caterpillars have long hairs that can cause skin irritation, so it is recommended to wear gloves.
For quick tips for insect removal or more information about this insect and where the above information was obtained, please visit the following links:
Frequently Asked Questions
About the European Gypsy Moth (LDD)
What is the European Gypsy Moth?
The European Gypsy Moth (Lymantria dispar dispar) or LDD is an introduced, defoliating insect that is considered to be a major pest in eastern North America. The caterpillar, or larva stage of the insect, eats the leaves of trees, making them more susceptible to disease and damage from other insects.
How much damage can the European Gypsy Moths cause to trees?
Tree damage depends on the degree of infestation, past defoliations, the tree's vulnerability. Defoliation can range in severity from light to almost complete defoliation. If the tree has been weakened or stressed by other conditions, and attacked repeatedly in recent years, severe defoliation can result in the death of the tree; however, most trees will recover from gypsy moth infestation.
What kinds of trees are most affected by the European Gypsy Moths caterpillar?
These 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 runs out of foliage of its preferred species, it will begin to feed on more than 300 vegetative species, like evergreens such as pine and spruce.
What is the lifecycle of the European Gypsy Moths?
The moths are seen only in mid-summer. They exist only to mate and after the female lays her eggs, moths of both sexes die. They lay their egg masses on the limbs and trunks of trees, on rocks, buildings, vehicles or in other sheltered areas. The masses remain in place all winter and will hatch the following spring from early to mid-May. Once hatched, the caterpillars begin to feed and continue for approximately seven weeks before pupating into moths.
Are there any natural enemies (control factors) to the European Gypsy Moths?
Yes. Predators include other insects like wasps, flies, beetles, ants and spiders as well as birds such as chickadees, blue jays, robins and nut hatches. Animals such as chipmunks, squirrels and raccoons will also prey on different life stages of gypsy moth. Diseases, caused by bacteria, fungi or viruses, and climate conditions contribute the most to keeping levels within a normal range.
Information for Residents
What can residents do?
Property owners are responsible for managing trees (and pests) on their property. Residents are encouraged to monitor trees on your property - look for egg masses in winter, caterpillars in spring, and pupae and moths in July and August - and take action to remove European Gypsy Moths as often as possible.
For City or private trees, residents can consider physical removal of caterpillars through various methods – burlap wrapping, spray with water, physically knocking caterpillars, etc. Pupae can easily be destroyed and disposed. Also, once the moths have laid egg masses these can be more easily removed and disposed. Some of these approaches are described on the City’s website.
Should property owners consider a commercial insecticide to help protect trees?
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. You should also be aware that pesticide applications do not produce an instant defence and will not completely eradicate the problem but can be very effective in protecting trees when used appropriately.
My family has been experiencing rashes that we think come from the European Gypsy Moth caterpillars. What should we do about this?
The hairs of the European Gypsy Moth 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. If handling Gypsy Moth, gloves should be used.
How can residents report specific areas/trees of concern?
The best approach for specific trees of concern is to call 3-1-1 or create a service request online. Staff will assess the health and condition of any City trees that are reported. It is important to note that most trees will be able to sustain themselves through the gypsy moth infestation; in most cases, they will produce a second flush of leaves once defoliation reaches more than 50%. Healthy trees are expected to be resilient to defoliation from the gypsy moth.
The City of Ottawa’s Role
What is the City doing to help manage this invasive pest?
The City of Ottawa is conducting Gypsy Moth surveys, which started in February 2021, throughout the urban and rural area to determine the extent of the outbreak. We have communicated with other stakeholders and partners such as the Ontario Ministry of Natural Resources and Forestry and they are monitoring the issue with increased populations of this insect in other areas of the province. City staff continue to monitor this issue and will communicate to residents about gypsy moth status in Ottawa and about best practices for residents to consider for control.
Why hasn’t the City done a broad aerial spray to manage European Gypsy Moths? Will it happen?
At this stage of the infestation, the City is not considering a spray program. City staff are monitoring defoliation and coordinating surveys to estimate insect populations. Based on the survey data and in consultation with experts and partners across Ontario, City staff are developing future response plans for gypsy moth that will include consideration of all available tools, including pesticide.
For More Information
Visit the City’s website to learn more about the European Gypsy Moth.
If you have questions about insects on City trees or questions about insect control, please call 3-1-1 or submit a service request online.