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Skip Navigation LinksSimcoe County > Departments > Forestry > Resources for Landowners > Gypsy Moth

Gypsy Moth

​​​​​​​​European 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 was observed in 2019.  Partial defoliation of trees has been noted within parts of the following local municipalities:

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

See link​ for a map of impacted areas​.

Simcoe County completed egg mass sampling in fall 2019 within affected County Forest Tracts to assess the population level of this insect and to forecast future impacts.  

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 overall 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.  Population monitoring will continue to evaluate the insect population to forecast potential future impacts.  This will ensure the use of appropriate management practices.  

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. 

Maintaining healthy trees and forests is an important defense against Gypsy Moth.

Gypsy Moth Population Chart.png 

(Source: MNRF, https://files.ontario.ca/mnrf-foresthealthconditionsontario2018.pdf)

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: