What are Gypsy Moths and what impacts do they have?

European Gypsy Moth (Lymantria dispar) is a non-native invasive insect that was brought to North America in the 1860s from Europe. It was first established in Massachusetts and spread to Ontario by 1969. It is now a well-established forest pest throughout much of the province.

Gypsy Moth larvae (caterpillars) feed on the leaves of over 300 host plant species, mainly hardwood trees. Some of their preferred hosts are oak, maple, birch and aspen, alder and pine, depending on the region. The larvae chew holes in vegetation or consume entire leaves, referred to as defoliation. A single Gypsy Moth caterpillar can eat an average of 1 m2 of leaves over its lifetime*. Typically, leaf loss of 50% or more of canopy cover is required for several years in a row to cause deciduous tree mortality* and some trees will regrow new leaves later in the summer. In addition to defoliation, Gypsy Moths are considered a pest for other reasons; Gypsy Moth caterpillars have irritating hairs which can cause discomfort to human skin and they produce a considerable amount of frass (poop) which is a nuisance to homeowners and forest users. 

Gypsy Moth populations follow a cyclical life cycle, experiencing population surges (outbreaks) approximately every 7-10 years. Historically during outbreaks, the population rises rapidly and is followed by a crash a few years later. Outbreaks are typically collapsed by naturally occurring factors including competition, pathogens, predators and parasites. Pathogens including the Nucleopolyhedrosis virus (NPV) and Entomophaga maimaiga (fungus) which attack the caterpillar stage and can cause increased mortality and a population collapse.

*Reference: Government of Canada (2013). Retrieved from https://www.canada.ca/en/health-canada/services/pest-control-tips/gypsy-moths.html


The Township of Georgian Bay is not currently spraying for the European Gypsy Moth.


 Understanding the lifecycle of the Gypsy Moth
  1. EGG
  • Laid in late summer and hatch in the following spring
  • Oval-shaped egg mass, 30-60 mm long
  • Covered in tan coloured hairs

2.  LARVA (Caterpillar)

  • Occur from April to July
  • Light gray to black with hairs
  • 6 pairs of red dots & 5 pairs of blue dots

3.  PUPA

  • Cocoons can occur from July to August
  • Dark brown shell


  • Moths emerge from July to September
  • Males are brown, females are white and cannot fly
  • Lack mouthparts and no longer feed on trees

Lifecycle of a Gypsy Moth

 How are Gypsy Moths affecting Georgian Bay?


As you can see by the mapping Georgian Bay Biosphere has provided, Gypsy Moths are prominent in our area. Populating exponentially in the last year. 


 What can you do to help?
  • From May to August hand-picking is an effective way to remove caterpillars, moths and pupae from smaller trees and shrubs. Place in a bucket of soapy water for 48+ hours. To attract natural predators of Gypsy Moth you can plant native shrubs and flowers.
  • From late June to August, large caterpillars may move down tree trunks during hot days. To target these, you can create a ‘skirt trap’ - wrap a large piece of burlap around the trunk fastened by twine or rope around the middle, fold the top half of the burlap over the twine so there is overhang that the caterpillars can crawl under. City of Toronto's instructional video. Check the trap every afternoon and place caterpillars and pupae in a bucket of soapy water for 48+ hours.
  • This method may also trap females in their moth stage (from July to August). The same steps can be applied.
  • During their egg stage, from September to April, egg masses can be scraped off surfaces (e.g. tree bark, sheds, lawn furniture, vehicles) into a container with soapy water for 48+ hours. SSEA's instructional video on removing egg masses. Egg masses that are on the ground are likely to survive through winter and hatch caterpillars in spring, so be sure to carefully collect egg masses in a container of soapy water.
  • If you notice dead caterpillars, it is best to leave them where they are. Dead caterpillars can be infected with the virus/fungus that are natural controls for the population. If left alone, the dead caterpillars can infect others and help spread these natural controls.
  • Please note: when handling or managing Gypsy Moth caterpillars, pupae, or eggs, use gloves. The long hairs can cause skin irritation or allergic reaction in some people


Additional Resources

Information from Georgian Bay Biosphere: https://www.gbbr.ca/ 

1. GBB Webinar on Gypsy Moths presented by Margaret Scott, Registered Professional Forester 

2. Gypsy Moth information package

3. Gypsy Moth Predators


Information provided by Severn Sound Environment Association: https://www.severnsound.ca/

  1. SSEA's Gypsy Moth Factsheet
  2. SSEA's YouTube Video on Gypsy Moth Life Cycle and Management Options.
  3. SSEA's instructional video on removing egg masses.
  4. SSEA and Township of Tiny Gypsy Moth webinar
  5. County of Simcoe’s Gypsy Moth page
    1. County of Simcoe EGM Survey Results 2020
    2. County of Simcoe – Gypsy Moth Infestation Status June 9, 2020
  6. Invasive Species Center – Forest Invasives Canada Gypsy Moth page
  7. Invasive Species Centre Webinar: Forests under attack: The history, dispersal, and management of gypsy moth
  8. Ontario Gypsy Moth page (including 2020 defoliation survey results)

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