Moth Madness: Managing Gypsy Moth Caterpillars

LDD moths on a tree trunk

We received a lot of great questions about Gypsy Moth caterpillars, which seemed to be everywhere in late spring. Gypsy Moths are an introduced species that go through three- to four-year population booms, and we are currently in year two of a boom. We asked CVC ecologist Laura Timms for more information on Gypsy Moths. Here are her top seven things to know about this species:

Male Gyspy Moth . [Picture: Flickr Creative Commons, Roger Wasley]
  1. Gypsy Moth caterpillars were introduced to the Boston area in 1869, by a man named Étienne Léopold Trouvelot. He thought that he would be able to use them to start a North American silk industry. He kept them in cages in his backyard and unfortunately, they escaped. Since then, Gypsy Moths have spread across the northeastern United States and eastern Canada.
  2. They eat the leaves of many different types of plants, but prefer hardwood trees like maple, spruce, elm, birch and poplar. They love oak the best. They also feed on garden shrubs and flowering plants.
  3. One year of Gypsy Moth feeding won’t kill a healthy, mature tree. Healthy hardwood trees will regrow their leaves. Small, diseased or stressed trees due to pests, pollution, drought or root compaction are more vulnerable. Back-to-back years of Gypsy Moth feeding can weaken a tree, making it susceptible to disease and damage from other insects. After two or more years of feeding, Gypsy Moths can kill a tree.
  4. Some people find exposure to Gypsy Moth caterpillars irritates their skin or throat. This is because caterpillars have small hairs on their bodies that can be dislodged into the air. If you find that you’re sensitive to these hairs, wear gloves if handling Gypsy Moths or avoid touching them altogether.
  5. As part of their ongoing Gypsy Moth control programs, the cities  of Brampton and Mississauga are carrying out a combination of ground sprays, tree injections, scrapping egg masses off trees and using pheromone traps, which are milk cartons that have female Gypsy Moth sex hormones inside the carton to attract males. The males get stuck to the carton, giving researchers a rough estimate of population density.
  6. CVC does not currently manage Gypsy Moth infestations in our conservation areas. Unlike Emerald Ash Borer (another introduced forest pest), Gypsy Moths rarely cause large-scale damage and management programs are very expensive. In addition, insect outbreaks play an important role in forest ecology. They create habitat for wildlife that use tree cavities and eat decaying trees, such as woodpeckers and the insects they feed on. Small gaps in the forest caused by a few dead trees can also make room for new plants and trees to grow.
  7. There are a few things you can do to reduce the number of Gypsy Moth caterpillars on your property. You can hand-pick caterpillars off of leaves, wrap burlap bands around tree trunks to collect caterpillars, and scrape egg masses off trees and destroy them. Check out the City of Mississauga’s resources for managing Gypsy Moth caterpillars on your property.
Female gypsy moths on top of egg masses. [Picture: Forestry Images, John Ghent]

Learn more about insects of the Credit River Watershed here.

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*Header image credit to Melissa Esposito

By CVC’s Kimberley Laird

Comments (28)

  1. They also, on my managed forest farm, like black cherry trees. I pull their tents apart in the evening and stamp or scrape them into the ground.

  2. We are relatively new to the South Mississauga area and worried the moths can destroy our new trees. Please advise where I can purchase the burlap to wrap around the base of my oak trees. Thank you.

  3. We live on St. Andrew’s Rd, Caledon East, close to the Devil’s Paintbrush golf course. This is the second year of gypsy moth infestation on our property.
    They are stripping the trees planted by the CVCC 4 years ago, also our willows, oaks, apple trees, and maples. We have squashed hundreds of them, and scraped off last year’s egg masses, but this year is especially devastating. My husband, Kevin Harper has emailed you with details, and copied the town of Caledon, our counselor etc. , with no response. We definitely need to have the spraying programme extended to Caledon. The invasion continues on township properties, ie. The Caledon Trailway and along St. Andrew’s Rd. are just 2 more examples.

    Thank you for your attention to this damaging invasive species.

    Vicki Clare and Kevin Harper

  4. I concur with the comments above by Vicki and Kevin – we need a spray program as well. I am in the Erin area. Other resources I have looked into have said gypsy moths can destroy vast amount of hectares in a forest at a time – the crown damage done to my red maples, magnolias (practically decimated now), and even blue spruce is horrible. I understand hard wood trees may re-leaf, (albeit smaller foliage, so less fantastic fall colours, and assuming tree is healthy enough), but what about the evergreen trees? Will my blue spruce re-needle where they have been chewed off? My smaller blue spruce used as decorative trees in my garden are almost denuded! I already lost a large mugo pine topiary to them last year.

    There must be something that can be done?? Are we climb on tall ladders and scrape these nuisances down and risk falling off the ladder? I suppose spraying them out with a pressure hose is one way… however with their nests forming now, need more force to break them apart, hence ladder climbing and physically knocking them off.
    Is there a homemade spray remedy? The organic spray recommended for them seems to be sold out everywhere.

    Many thanks,

    Elly Campioni

  5. I agree with the above resident. We live in the south west part of Caledon and we are inundated with Gypsy Moth. Too little too late we now have the information we require on how to control on our own property. The Town of Caledon needs to step up its information to residents on practical methods we can do but also begin to also run programs across Caledon similar to those mentioned in Mississauga. We are supposedly a ‘green” community but soon will not be due to unchecked gypsy moth infestations. Might I suggest the CVC be our advocate to the town???

  6. I concur with Victoria Clare. These things are everywhere and are ruining my trees and gardens. I am also on St. Andrews near the golf course. How can I manage my forest with this pest present?

  7. I read with interest your email about gypsy moth catepillars.I followed the link and also read with interest some of the comments left by residents.Living on a 25acre property really makes some of the control measures unrealistic … wrapping burlap on tree trunks and drowning caterpillars in soapy water????  I could have started wrapping in March and I still wouldn’t be finished today, let alone picking caterpillars.Only option I see is spraying in rural areas. I tried looking for pheromone traps for the adult males … my order status since 2 weeks has been ‘Awaiting Fulfillment’ . Calling the store I am told, that product hasn’t arrived yet.  Why I ask myself? Most likely, because gov’t agencies and private contractors have purchased all of it … none to be had.Really not much we can do … it is very discouraging.Susanne

  8. We need help!!! Our huge maples and young Pine Oak on our property are so infected with the Gypsy moths. The white females are laying huge masses of eggs all over the bark and crotch of the branches. We are in the hamlet of Brimstone at the Forks of the Credit (272 Dominion st). There are way too many for us seniors to scrape off. Please advice. Thanks muchly

  9. Maybe you all need learn to live with the damage. The harm from spraying your property has to be weighed against the harm from the moths. Are you in favour of killing lots of other insects at the same time just to kill the moths? What about the damage to our health and our children’s health. Spraying isn’t some guided missile that only kills these caterpillars. The genie is out of the bottle and we have to live with it.

    1. Hi Tom. The pesticide used to treat Gypsy Moths caterpillars is a bio pesticide. The active ingredient is a naturally occurring bacteria found in soil (Bacillus thuringiensis var kurstaki or Btk). It’s highly specific to certain species of moth and butterfly larvae. It’s only effective when applied in the correct time frame – when the caterpillars are very small but are actively feeding. The spray works on Gypsy Moth larvae by coating the leaves that the caterpillars eat. Once ingested, the bacteria release a chemical inside the caterpillar’s stomach that acts as a poison and kills the caterpillar.

      The spray is considered non-toxic to all other life forms. However, it can kill other moth and butterfly larvae if they happened to be in the same age range as the Gypsy Moth caterpillars and feeding on the same trees at the same time. This is why sprays are used as a last resort and only when the Gypsy Moth populations are very high and the risk to tree health and subsequent food for other animals and insects is also high. Otherwise, treatments such as egg mass scraping, tree banding, and pheromone traps are used as the sole means of control.

  10. Hello, I live in Caledon East on Innis Lake Road. We have been inundated with swarms of Gypsy Moths. We have wrapped our tree trunks with plastic wrap, sprayed with soapy water. Driving up or down our street, it appears that multiple trees are effected. Back in May, my arms had very bad rashes. Only after doing research, I found out that the rashes came from caterpillar hairs. It swelling and itching lasted about 4 weeks. It was so painful. We had caterpillars all over our backyard. The town needs to go something about this regardless if on town property or not.

  11. Hi, My wife and I live in Inglewood and the gypsy caterpillars, moths and now egg nests on our trees are out of control. We have a number of trees with large clumps of white moths leaving nests. There are too many for us to scrap off, let alone risk breaking our necks on ladders. Please advise where we can get help before these hatch next Spring.

  12. We are infested with these horrible moths. We are looking to get spraying done from helicopter. We live in the Ganbrook area and had them sprayed years ago but not sure who we used. Can you send me the info please. Thanks

  13. Hello! My husband and I moved into the area recently and have been appalled by the number of Gypsy moth caterpillars and now moths that have over run our 25 acre property. We have been picking them off, wrapping trees and deploying pheromones but the sheer volume has been overwhelming. The moths are now declining but there are gazillions of egg masses every where. I learnt from your site that we are in year 2 of a 4 year cycle, and I realize more needs to be done to try to turn the tide for next year. I would be very grateful for a referral to someone who could help me. Thanks in advance.

  14. My husband and I live in Terra Cotta and have been inundated with these Gypsy moth caterpillars this year. Seemed like thousands of them on our trees. Pooping all over. Our neighbors have experienced the same. I haven’t been able to even sit on my front porch. I’m all for spraying them. I think ridding the area of them far outweighs any potential to kill other bugs. I say save our trees before we don’t have any left. The CVC should give more information about how to fight these pests and earlier in the year. I hear you can wrap your trees in March before the eggs hatch and spread tree tanglefoot. We only have a few trees to wrap. Others have many more and it definitely wouldn’t be feasible to do or even realistic.

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