Have you noticed Mount Royal isn't as green as usual? Caterpillars are to blame

The adult male moths are brown and flighted, while the females are larger, white and flightless. But the adults aren’t really the problem. It’s the kids. Or, scientifically speaking, the larvae.

Gypsy moth caterpillars are hungry and they can strip a tree bare

Gypsy moth caterpillars chomping their way through Mount Royal canopy

2 years ago
Duration 3:16
Patches of the park are bare as the insatiable invasive species infests much of southern Quebec.

Mount Royal's usually dense tree canopy is quickly becoming a symbol of southern Quebec's infestation of gypsy moth caterpillars.

"It was always very, very green and now the top of it is completely dead," said McGill University student Leyla Bahmany, describing her view from home of Mount Royal.

Lymantria dispar dispar is the official name, or LDD for short, of the caterpillars doing the damage. LDD moth is the name preferred by Ontario's invading species program, which says the more common name, gypsy moth, is derived from a culturally offensive slur.

The LDD caterpillars grow up to six centimetres long. They're hairy and can be identified by the blue and red spots on their backs.

The adult male moths are brown and flighted, while the females are larger, white and flightless. But the adults aren't really the problem. It's the kids. Or, scientifically speaking, the larvae.

On Mount Royal, and in many forests in southern Quebec and Ontario, the furry larvae can be seen crawling on tree trunks, sometimes in enormous numbers.

They eat all the leaves

An entomologist at the Université de Montréal, Etienne Normandin, said they're easy to spot in Montreal parks as "they will be at the base of the trunk."

Gypsy moths lay their eggs on trees in masses that look like white bulges. 

The larvae hatch and eat the leaves — all the leaves. These are very hungry caterpillars.

The larvae have voracious appetites and they aren't picky eaters. They feed for about twice as long as many native caterpillars.

Gypsy moth caterpillars are stripping trees bare across southern Quebec and Ontario. While that doesn't kill the trees outright, it can leave them vulnerable. (Oliver Walters/CBC)

Trees can be stripped bare, and that has been noticeable on Mount Royal as of late. There are barren patches of leafless trees all over the park.

While this leaf feast doesn't necessarily kill the tree outright, the trees are left more vulnerable, Normandin said, and thousands of trees may be lost as this year's wave of LDD larvae is considered severe.

Normandin said the trees can be invaded by other pests, or be more fragile during a summer drought.

"During severe outbreaks, trees and shrubs are completely defoliated over large areas," says Natural Resources Canada on its website.

"Despite the trees' ability to produce a new crop of leaves over the summer, the damage causes significant growth loss."

The caterpillars are eaten by some birds and mammals, but there are too few predators to put a dent in the population.

'Exceptional situation,' Ministry of Forests says

A government spokesperson told CBC News that gypsy moth infestations don't generally threaten the survival of healthy trees and there are more dangerous insects out there, but officials are keeping an eye on the infestation.

"This is an exceptional situation," said Pierre Therrien, an entomologist with Quebec's Ministry of Forests, Wildlife and Parks. "Usually in Quebec, there aren't that many gypsy moths, but this year there are high populations all over."

WATCH | Gypsy moth caterpillars found all over Canada:

Climate change makes invasive moth caterpillars a bigger problem

2 years ago
Duration 2:02
LDD moth caterpillars, once known as gypsy moth caterpillars, have invaded forests and parks in Ontario and some parts of Quebec, and climate change is turning them into a bigger problem.

This caterpillar epidemic is due to a mild winter and hot, dry spring conditions that favoured the insect, the entomologist said.

In Ontario, hundreds of thousands of hectares have been affected by the caterpillars and now officials like Therrien are worried about what's happening in Quebec.

Caterpillar history and how to fight back

The spongy caterpillar was brought to Massachusetts, U.S., in 1869 by Étienne Léopold Trouvelot, a French entrepreneur who wanted to enter the silkworm business.

It took a few decades before it arrived in Canada, but its first appearance was in Quebec nearly 100 years ago in 1924, according to Natural Resources Canada's website.

There were massive eradication campaigns that targeted the eggs, but the gypsy moth proved relentless — showing up again in 1955 and spreading west to British Columbia and as far east as Nova Scotia, the website says.

"To protect isolated or ornamental trees, it is recommended that egg masses found in the fall on trees, stones or any other object be collected and destroyed," the website says

"In June, mature larvae can be collected when they congregate in shady areas by banding the base of the trunks with tar paper."

with files from Radio-Canada


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