There's a tent caterpillar outbreak on Vancouver Island — but no need to panic, zoologist says

Tent caterpillars appear to be out in full force on Vancouver Island this year, spinning their silk on tree branches to form a white web wrapped around the leaves.

Walk along the Harbourfront Walkway in Nanaimo, for example, and you'll see these fuzzy creatures dangling from trees and even falling down on passersby. 

According to Judy Myers, a zoologist who has been studying tent caterpillars on and around Vancouver Island for 48 years, they were due for an outbreak. She says tent caterpillar outbreaks happen every eight to 11 years, and the last one was in 2012. 

"This one took a little bit longer to develop, but it is a normal thing," she told On The Island host Gregor Craigie, adding that this year's outbreak is one of the largest she's seen. 

Tent caterpillars are colourful and fuzzy, and about 2.5 centimetres long. 

They begin producing silk as soon as they hatch, and because they live in groups, that silk builds up to form tents. Tents are used for caterpillars to bask in the sun and warm up their body temperature, which helps them mature, Myers said.

If temperatures soar like they have done recently in B.C., they also build silk tents in shady spots to help cool them off. 

As they moult, they go inside the tent to protect themselves from parasites, Myers added. 

While it might be a little unsettling to see them grouped together, building a tent and wiggling around, Myers said the caterpillars are harmless. The trees will typically survive, although fruit trees may not yield a crop in the summer tent caterpillars have been around. 

"In general … trees will come back out into leaf later in the summer and you tend to forget there even were caterpillars,' she said. 

Last week, the City of Nanaimo posted on social media that it won't typically do anything to stop an infestation of tent caterpillars unless it's harming a fruit tree or causing problems in a busy area. 

Myers said it's best to treat trees before an infestation happens, but if it's already happening and you want to get rid of the caterpillars, clipping off branches where they've built tents and destroying them is a good place to start. 

Additionally, trees can be sprayed with a bacillus thuringiensis (B.t.) spray. According to the province, B.t. is a bacterium found naturally in soil and water that can cause illness in many insect larvae, including caterpillars.

But if Myers sees tent caterpillars near her Vancouver-area home, she leaves them alone.