TORONTO -- Picture a hairy five-centimetre-long caterpillar that can drop from tree branches onto unsuspecting passersby, has few natural predators, and can coat a tree trunk so thick you can knock them off by the hundreds with a broom. This is the gypsy moth caterpillar, and it is your creepy-crawly nightmare of the summer.

The gypsy moth caterpillar is no joke. The invasive species arrived in Ontario about 50 years ago and has been a periodic menace to both people and trees since the early 1980s. There are outbreaks every seven to 10 years, according to an Ontario government website, although this year’s outbreak follows one last year which caused nearly 590,000 hectares of defoliation, up from about 47,000 in 2019.

“They're kind of creepy to see and the other problem is that they eat a lot. They’re hungry, hungry caterpillars and they can take out huge areas of trees and bushes,” CTV science and technology specialist Dan Riskin told CTV’s Your Morning on Friday.

“Last year… the area of trees that lost all their leaves in Ontario was about the size of Prince Edward Island, so they do a significant dose of damage and it looks like their numbers are very high this year as well.”

To make matters worse, the hairs on their legs can also cause an allergic reaction in some people.

Their eggs will often live in the winter on the bark of trees, but it is in the spring and early summer when the larvae climb the trees to eat on foliage.

Like many successful invasive species, the gypsy moth caterpillar is adept at transporting itself to new feeding areas. One way it does this is by ‘ballooning’, or hanging off the end of a branch on a tiny thread and allowing the wind to carry it to a new area. They also use ground transportation, says Ruskin.

“These egg masses really are the trick. They leave those on trees but they also leave them on sometimes patio furniture sometimes under the bumper of a car and so it's pretty easy for them to move around,” he said.

In a summer where getting outside and into nature seems to be a victory, the arrival of the caterpillars instead now has many worrying how to deal with the infestation.

One option that many have tried is to wrap tree trunks in burlap bands, which can catch caterpillars as they move up and down the tree. Others have wrapped trees in sticky substances such as duct tape to trap the caterpillars.

Then again, there’s also the time-tested approach of chemical warfare.

“There are some interesting pesticides that are based on bacteria that make this species sick, but don't affect other species and are not harmful to humans that are quite exciting and so it may come down to spraying with these biological control methods, but that hasn't been effective yet and so that needs to ramp up,” said Riskin.