Now is the time for homeowners to strike back against gypsy moths

They're invasive, they defoliate trees and they need to be destroyed. The best time to prevent gypsy moths from coming back in the spring is to remove their egg sacs from trees this fall.

The invasive insects defoliate trees and can take over your yard

Jill-Anne Spence, the manager of urban forestry for the City of London, removes gypsy moth egg masses from trees in Fairmont Park in London, Ont. (Travis Dolynny/CBC)

They're invasive, they eat the leaves off trees, and if you ask anyone who's had to deal with them, they're disgusting.

Gypsy moths were brought to North America more than 150 years ago by French artist and amateur entomologist Étienne Léopold Trouvelot, who had high hopes for the insects.

"[Trouvelot] was trying to breed the North American silkworm with gypsy moths to create a silk industry," said Jill-Anne Spence, London's manager of urban forestry. "The moth escaped and became established in the eastern borders of Canada and the U.S."

Since escaping the well-intentioned but unfortunate plans of Trouvelot back in 1869, the gypsy moth has spread west across North America, with varying degrees of infestation.

"What's so problematic about the gypsy moth is because it is non-native, there's not a lot of natural predators that can impact it," said Spence. "It really enjoys our structural trees, the bones of our urban forests, such as oaks, but they'll pretty much impact anything."

Gypsy moths in London, Ont.

2 years ago
Duration 2:19
Gypsy moths were back in a big way in London, Ont. this year. Jill-Anne Spence is the manager of urban forestry for the City of London.

According to Spence, one gypsy moth caterpillar can defoliate up to one square metre of a tree's canopy, severely threatening the tree's health. The caterpillars are black with a series of red and blue dots on their backs.

"They're cyclical in nature, and they go through peaks and boons. About every ten years, they will have a population increase."

2020 is one of those years, where London's Byron neighbourhood, which is home to a wide array of broadleaf trees, has been hit incredibly hard by the gypsy moth. In some areas of the community, caterpillars take over the trees, sidewalks, backyards and swimming pools. Frass, or caterpillar droppings, rain down from the trees.

Gypsy moth caterpillars crawl on a tree outside London, Ont, in 2020. (Travis Dolynny/CBC)

The City of London tries to combat the moth, treating some 6,000 trees along residential streets in Byron this year alone. Fairmont Park in east London has also been taken over by the gypsy moth.

There is a natural gypsy moth virus disease, often called wilt, that contributes to slowing the spread of the moths following a population peak, but it does not eliminate them.

So what else can be done to stop them?

The gypsy moth's lifecycle is the same as any paraphyletic insect that starts with an egg, hatches into larvae in spring, cocoons into a pupa and then emerges as an adult moth in mid-summer.

Female gypsy moths are white with a brown streak across their back and cannot fly. Male moths are smaller, brown and can fly. (Michael Charles Cole/CBC)

Females can lay a group of 100 to 1,000 eggs on a tree that are covered in a tan-coloured sac. That's when they need to be scraped from the tree and destroyed in the fall or winter.

How to scrape and destroy the eggs

If you spot gypsy moth egg sacs, you'll need these five things:

  • Gloves.
  • A small flexible scraper (plastic is best as to not damage the tree).
  • A spray bottle with water.
  • A container to catch the egg sacs.
  • A bucket of soapy water with a lid.

Then you'll want to spot the tan-coloured sacs.

A number of gypsy moth egg sacs on a tree in Fairmont Park in London, Ont. (Travis Dolynny/CBC)

"[The egg sacs] are going to be in places where they're somewhat sheltered so they'll be protected throughout the seasons," said Spence. "They'll be on the undersides of branches ... in the leaf litter, and you can also find them in places like vertical surfaces along your garage, the mailbox, even in your woodpile."

Once you find an egg sac, spray it with water, position the container under the sac and then scrape upward, letting it fall into the container.

How to remove gypsy moth egg sacs

2 years ago
Duration 2:40
Jill-Anne Spence, the manager of urban forestry for the City of London, explains how to remove gypsy moth egg masses.

Once the sacs are removed, drop them into the bucket of soapy water and put a lid on for at least 48 hours. The soap will suffocate the eggs and kill them. A lid will keep the smell of the eggs at bay, and Spence says its a good idea to wash all of your equipment to prevent any loose eggs from surviving.

The City of London is working on expanding their gypsy moth response by implementing a multi-year monitoring program, which is expected to inform management options for 2021. They'll take into account data from sampling points, tree defoliation and egg mass counts. For more on the city's response to gypsy moths, visit its website.


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