When the wasp swarm attacked a climber on a trail north of Vancouver this week, her reaction was so severe she needed helicopter evacuation.
But Maria Masiar, search manager with Lions Bay Search and Rescue, said the wasps weren’t done, attacking rescuers, and then another group of hikers who were sent scrambling by the same stinging swarm when they came across the scene.
Pest control expert Mat Neale said he had seen a “dramatic increase” of wasp calls in British Columbia, as warm weather and abundant food contributed to a late summer surge in numbers of the stinging insects.
Backcountry and rescue groups have been warning against the unusual number of wasps on popular trails.
Neale, manager at Solutions Pest Control in Metro Vancouver, said wasp activity in the past few years had been quite low, but technicians were now dealing with eight to 10 calls a day.
He said warm and dry temperatures, and a recent boom in the population of hemlock looper moths — a prime food source for wasps — had contributed to the spike in wasp activity.
“Once it gets warm enough for their food sources to wake up, then so do they,” said Neale, “They follow the trend of most insects during the summer, and they like the heat and dry, and we’ve had an abundance of all of the above.”
Masiar said she spoke to the climber who was attacked on the Redoubt Wall trail and she was recovering after being stung up to 20 times.
A 911 call had suggested she was stung about 100 times on Tuesday, but Masiar said medical teams believed the initial number was “an overestimate” after assessing the climber, whose body was covered in hives as a result of a systemic reaction to the stings.
Masiar said the same swarm attacked the rescuers, as well as the second group of hikers who were stung about 20 times when they passed by an hour later, forcing them to flee.
The rescue group had earlier warned hikers that wasps across the province were getting “fierce.”
The group said nests of ground-nesting wasps in southwest B.C. are often hidden beneath rocks, logs or vegetation next to trails.
“By August and September, a single colony may contain hundreds to thousands of worker wasps, all protecting the nest and searching for food as natural food sources become scarce,” the online warning said.
Neale said yellowjacket wasps usually get “very aggressive” this time of the year. Nest locations can vary from “a mouse hole in the ground or they can build a nest in the soffit of your house, or in the attic somewhere, or even in a wall,” said Neale.
He said he had recently hiked on Gambier Island in Howe Sound, and his group passed about nine visible inbound wasp nests.
“Just because we’re passing through, someone kicks a log, and boom, they all come out,” said Neale.
Neale said he was the only hiker in a group of nine who didn’t get stung on the hike.
The Squamish Off-Road Cycling Association warned last month that riders should avoid ground nests by staying on established trails and keeping dogs close or leashed, and carry an EpiPen or allergy meds in case of an allergic reaction.
“Keep moving if you hear buzzing or notice activity near the ground; do not swat or linger,” it said.
An online “wasp watch” map based on data provided by hikers in the Sea to Sky area and the Fraser Valley marks the sites of dozens of recent encounters.
It includes a reference to a previous attack on the same trail where the climber was stung: “On the descent right beside the rope pull there is a big wasp nest. Was swarmed and stung a dozen times,” the Aug. 16 post says.
Other than ground-nesting wasps, Neale said bald-faced-hornets are second on his watch list.
Bald-faced hornets tend to built visible nests in trees, up to the size of a basketball, said Neale.
Unlike bees, wasps can sting an almost unlimited number of times, said Neale. Yellowjackets in particular can sting “to their heart’s content” or until their venom sacs are depleted, with one wasp’s sting inviting others to join in.
The only defence is to run.
“Twenty wasps in the area you could get stung 60 to 100 times if you don’t remove yourself,” he said.
This report by The Canadian Press was first published Aug. 27, 2026.
By Non Shen | Copyright 2026, The Canadian Press. All rights reserved.
