Caterpillar army on march in Whistler 

Whistler is under attack by an army of tenacious, voracious tent caterpillars.

"This is the worst year we have ever had," said the municipality’s landscape supervisor Paul Beswetherick.

"It is one of those boom and bust things where the population in my estimation has been growing since 1994.

"Each year it has got progressively worse."

Although the invasion may feel like something out of B movie it is in fact just part of a natural cycle.

No one really knows what triggers the boom in bugs, but boom they do.

Beswetherick hopes Whistler is hitting the peak of its boom cycle now. "Hopefully it will be better next year," he said.

One reason for the reprise will be a corresponding boom in predators thanks to an abundance of food.

Birds do eat the caterpillars. But, said Beswetherick, they are not our feathered friends’ favourite meal.

"The birds eat the caterpillars but they have the coloration of things that are not too good to eat so most birds generally stay away," he said.

However, when the caterpillars pupate into moths it’s a feeding frenzy for fowl.

"The birds love the moths and so do the bats but that is a bit late for us as we have to deal with the defoliation and the crawling around on the roads and trails," said Beswetherick.

There is even a microscopic fly, which lays its eggs on the caterpillar. The maggots burrow into the caterpillar and kill it.

The municipality does not spray agents to kill the pests for the most part. But accessible tent nests are removed inside park areas.

While they are considered harmless to people, pedestrians are plagued by the creepy crawly caterpillars as they walk sections of the Valley Trail. The hairy hoards hitchhike on hair, clothing, strollers and anything else they can find their way onto.

It is almost impossible to avoid stepping on them, running over them, or squashing them there are so many around.

And they are devastating acres of trees.

Look up and you will see their nests which resemble large cobweb tents at the joining of several branches. There can by half a dozen or more tent-nests in each tree.

There is no easy way to get rid of the ravenous crawlers, which prefer to munch on aspen trees but will also eat willow birch alder and cottonwood.

For the most part trees are not harmed by the infestation. But if a tree is already stressed, said Beswetherick, a caterpillar invasion will kill it.

"To an unhealthy tree it poses a significant risk," he said.

"But to a healthy tree no, there is no risk. It is just one of those natural things that will cycle through and hopefully next year we will see a decline."

The main impact of tent caterpillar feeding on deciduous trees is a reduction in the rate of growth.

Vigorously growing trees can tolerate up to two or even three consecutive years of heavy defoliation without suffering serious damage or mortality. If a prolonged defoliation cycle occurs, (four or more years), moderate to heavily defoliated trees may experience a reduction in growth, suffer branch dieback and could eventually be killed.

In 1990 an army of forest tent caterpillars marched on vegetation around Prince George and stripped bare 108,290 hectares of deciduous trees. That was more than double the amount the pests had consumed just two years before.

The best way to deal with them in your backyard is to pinch off larvae-infested buds and dispose of them in plastic bag. After the caterpillars have hatched they can be fought with insecticides.

You can also prune and burn the tree branches supporting their nests.

There is little point spraying when the caterpillars are inside the tent, as the chemicals cannot penetrate the cobweb-like enclosure.

Once the caterpillars turn into moths look for their eggs, which are laid as three centimetre clusters on young branches and resemble brown Styrofoam. Scrape them off and destroy them.


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