Quick and Comprehensive Guide to Gypsy Moths

Hi All,

A lot of information has been circulating about gyspy moths so I wanted to put together a quick info guide for our members. One of the remedy methods has a March 1 deadline, so I hope this information helps you make an informed decision.

Quick Information:

  • Gypsy moths typically have an outbreak every 7-10 years.
  • Their infestation can lead to growth loss and high mortality rates of trees.
  • Targeting the eggs or caterpillars is the most effective form of action. 
  • Remedies includes: homeowners killing egg masses, trapping female moths, spraying of bacteria either through a licensed arborist or by homeowners (some sprays are limited to use only by licensed arborists)

What are gypsy moths?

They are an invasive defoliator species (meaning they eat leaves) from Europe that feed on a variety of trees. The Ontario distribution has shown preference to oak trees, but they also have been targeting birch and aspen trees in northern Ontario, and hardwoods such as sugar maple, American beech, and softwoods such as eastern white pine, and Colorado blue spruce in Southern Ontario. This species typically has an ‘outbreak’ every 7-10 years.


What is their life cycle like?

Gypsy moths follow a typical moth life cycle. In spring, eggs hatch and larvae ascend the trees to feed on the new foliage. Feeding is commonly done during the day early in this stage, but as the larvae mature the feeding shifts to overnight. Feeding is done by the end of July, (by now the pupa have turned into moths) and eggs are laid in the bark of trees to overwinter. 


What damage do they do?

While feeding, larvae chew holes in tree leaves or eat them entirely. Despite the tree’s ability to produce new leaves, in large outbreaks foliage can be completely eaten leaving a tree defoliated. Damage can be survived once or twice by healthy trees, but older trees may be more susceptible to defoliation, which causes stress. Further, one has to consider implications of drought, attack of other organisms, lack of energy reserves for winter dormancy, and then lack of energy for spring growth – all inhibited by defoliation. This damage can cause severe growth loss and high mortality of trees.

Caterpillars can also be a nuisance from their crawling and thus the droppings they leave on patios, outdoor furniture, cars, driveways and so on. Exposure to gypsy moth hairs, silken threads, and shed skins can cause skin rashes and upper respiratory tract irritation in some people. 

Once eggs are laid, they can be seen covering the trunk and branches of trees, affecting natural processes. At this stage, they can be easily spread to areas where the moth is not yet established.


What are some challenges to preventing/dealing with infestation?

  • Feeding in the mature larvae stage occurs overnight so it is difficult to spot infestation.
  • Difficulty to reach the height of affected trunks/branches of trees to apply control measures.
  • Young caterpillars may be blown in from adjacent infested properties in the spring.


What are some remedies?

Preventative action is preferable to reactive action. There are a few things we can do before we get into spraying insecticides or bacteria. Below are some actions that we can take immediately:

  • November through to Late April: 
    • Homeowners can scrape the egg masses off of the trees (can be seen from mid-summer through to the next spring) and throw them in soapy water (insecticidal soap, mineral oil, or a soybean oil product) for a minimum of 48hours, burn them or destroy them. Simply scrapping them onto the ground will not destroy them. The destruction of each egg mass prevents the hatching of up to 1000 caterpillars.


  • Late April to Late May:
    • “Tanglefoot Pest Barrier” can be placed around tree trunks to help curtail the caterpillars movement into and out of the tree canopy.
    • Placing sticky barriers (ex. inverted duct tape) on the tree trunks to prevent young caterpillars from crawling up the tree. 
    • Plant herbs, flowers and shrubs to attract birds that eat caterpillars and moths.
  • Late May until Late August: 
    • One can wrap a piece of burlap around an infected tree, leaving a lip hanging over to trap female moths when they crawl into the burlap. Once trapped, squish or submerge in soapy water to reduce caterpillar numbers. It is important to note that applications against the adult stage are much less effective than targeting the eggs or caterpillars.
  • Beginning of May- Mid June: Consider bacteria treatments such as Bacillus thuringiensis kurstaki-based products. 
    • Bacillus thuringiensis kurstaki (Btk) is is a naturally occurring bacteria found in the soil, not a chemical, and it works by producing proteins that are toxic to larvae. It must be ingested by feeding caterpillars for the endotoxin to work; it is not effective against the pupa and adult of the gypsy moth. Generally, two applications are made, one during late April or early to mid- May, followed by second treatment about 1 to 2 weeks later. This bacteria is:
      • currently the most widely used insecticide in forestry in Canada*
      • safe for the environment and its various components*
      • since its introduction in the 1960s, no human health problems have been proven to be attributable to its application*
      • is considered by most people to be the safest bioinsecticide available at present*
      • does not affect adult moths and butterflies, including the monarch butterfly, nor does affect other insects, honey-bees, fish, birds, or mammals

*The above information is taken from a study done on the safety of the subject bacteria by the Pacific Forestry Centre for the Government of Canada, 2007.

  • Natural predators:
    • Proliferation of the fungus Entomophaga maimaiga (a Japanese fungus that targets only gypsy moths);
    • a virus (Nucelopolyhedrosis) and;
    • a small wasp (Encyrtidae family)


  • March 1, 2021 deadline: ZimmerAir Services is offering Btk services via aerial application. Due to the overwhelming response of applicants for this year, they have moved their deadline to March 1. As Pat mentioned, please contact Daniel Haught (dhaupt@zimmerair.com), call 905-512-0538 for information, or visit their website at https://zimmerair.com/services/aerial-application-services/forest-pest-control/

Please note, as of now, from my own research I do not see any other companies or arborists in the area that offer similar services. There may be arborists that can be hired to apply Btk treatment to trees on your property that are inaccessible. Btk is also available for purchase at retailers, some products include:

Hope this helps you make an informed decision!


Maria Kaczmarek                                                                                          Lake Steward                                          lakestewardship@steenburglake.com

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