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Gypsy Moth

Gypsy Moth (Lymantria dispar) is a non – native invasive insect from Europe that was brought to North America in the 1860's.  First established in Massachusetts, it had spread to Ontario by 1969.

The gypsy moth larvae (caterpillar) feed on the leaves of many deciduous tree species, including red oak, white oak, poplar and white birch.  The caterpillars can consume a significant amount of leaves. 

An increase in European Gypsy Moth feeding within the County of Simcoe has been observed in 2019.  Partial defoliation of trees have been noted within parts of the following local municipalities:

  • Midland
  • Penetanguishene
  • Tiny Township
  • Adjala-Tosorontio Township

The Ministry of Natural Resources and Forestry (MNRF) monitor overall forest health annually throughout the province using aerial and ground surveillance.  2018 European Gypsy Moth surveys showed minimal impacts to Simcoe County.   Updated mapping will be available in fall 2019.2018 EGM Map.JPG

 (Source: MNRF,

To further monitor the impacts from European Gypsy Moth, Simcoe County will be completing sampling in fall 2019 within affected County Forest Tracts to assess the current population level of this insect. 

Although a few areas within the County are seeing some moderate defoliation in 2019, the current level of impact is not considered a major concern to forest health within the region at this time.  Defoliation levels of 50-60% and repeated annual defoliation are usually required to cause mortality of healthy trees.  As such, the County Forestry Department will not be considering any control operations in 2020.    Population monitoring will continue to evaluate the insect population to forecast potential future impacts.  This will ensure the use of appropriate management practices.  Maintaining healthy trees and forests is an important defense against Gypsy Moth.

European Gypsy Moth impacts are cyclical with high impacts occurring approximately every 7-10 years.  The most recent outbreak in 2008 was much less severe than previous outbreaks recorded in 1985, 1991 and 2002.  When populations rapidly rise, they are typically followed shortly after by a crash due to competition for food or mortality from a host specific virus or fungus.  Extended periods of extreme cold weather also reduce survival of above ground egg masses. 

Gypsy Moth Population Chart.png 

(Source: MNRF,

For further information, please visit:

Homeowners Management Guide to European Gypsy Moth

Landowners Management Guide to European Gypsy Moth 

Ministry of Natural Resources and Forestry - European Gypsy Moth

To contact a Certified Arborist or Professional Forster, please visit: