Scientists warn that 2021 will be bumper crop year for gypsy moth caterpillars in areas like the Island

Scientists are warning that 2021 will be a bumper year for European gypsy moth caterpillars.

SAULT STE. MARIE – Scientists have been warning that 2021 appears to be looking like it will provide a bumper year for the invasive gypsy moth caterpillar in areas like Sudbury and Manitoulin Island. And while they may only grow to be about four to six centimetres long, these invasive species are a large threat to Ontario’s forest cover.

“European gypsy moth caterpillars and other varieties of them have been in Northern Ontario for quite some time,” said David Dutkiewicz, an entomology technical with the Invasive Species Centre in Sault Ste. Marie, last week. “They first arrived in Ontario in the late 1960s in the Kemptville area, and were first brought to North America around 1860 by a French entomologist who hoped to cross-breed them with silkworms. However, these two species are not compatible to breed. It ended up a couple of gypsy moths got away in Massachusetts and things progressed from there.”

The European gypsy moth (Lymantrai dispar dispar L.) is native to Europe and is currently established in the Northeastern United States and Eastern Canada. You may find the insect in not only portions of Ontario, but in Quebec, New Brunswick, Prince Edward Island, and Nova Scotia. 

This year in Ontario, reports are pouring in of unusually high numbers of European gypsy moth. The larva (caterpillars) feed on foliage of a wide range of hardwood and some softwood trees. The gypsy moth has over 300 known host plant species, 150 of which are preferred hosts, he said. Some of these include oak, maple, birch, alder, hawthorne, poplar and spruce.

“People will definitely see them this year,” said Mr. Dutkiewicz. “The biggest area they have been found is Sudbury in the Northeast region area, and they have scattered populations on the Highway 17 corridor and Manitoulin Island. He noted, “last year was one of the largest defoliation events in Ontario,” with defoliation of trees caused by European gypsy moths in Ontario having increased from 47,203 hectares in 2019 to 586,385 hectares in 2020. This includes both light and moderate to severe defoliation mapped in the southern region (561,469 hectares) and 24,916 hectares mapped in the Northeast region.

All selected districts reported an increase in area defoliated from 2019. Defoliation caused by gypsy moth was most severe in forest stands containing species of oak, maple, poplar, willow and other broadleaf trees. In some areas, gypsy moth defoliated conifer species including eastern white pine.

In the Northeast region, the Sudbury District had the largest area of moderate to severe defoliation of 25,262 hectares.

“They are just starting up for this year,” said Mr. Dutkiewicz. “Lots of people have seen the furry caterpillar basically everywhere this spring. Unfortunately, they lay eggs everywhere: your shed, house, porch, wherever.”
“Each caterpillar eats about one square metre of foliage a day,” stated Mr. Dutkiewicz. 

Landowners can help battle the bugs using as little as burlap and soapy water. He suggested you can wrap a band of burlap around a tree. As the caterpillars come down from the canopy of the tree during the day, they will take shelter under the burlap. Then the landowner can visit the tree later that evening For a full list of ways to control European gypsy moths go online to (×3305-2021-04-09.png.

Mr. Dutkiewicz pointed out a good power washer can be used to get rid of the eggs in an area.

He noted that the insect is not a benefit in any way. “No, really they don’t do anything that is good. The provide a food source for mice and birds, but for the most part they are not good for the environment, or anything else for that matter.”

In May, gypsy moth caterpillars are only about one centimetre in length, clumping together on a tree near where their mother laid the egg mass the previous year. Once they start to grow, they develop a distinct pattern of blue and red dots down their back and grow, “really big tufty hairs all over their body.”