Butterfly sightings in Metro Vancouver plummet

Fewer butterflies are flying around Metro Vancouver this year, and their scarcity is leaving scientists and community members with more questions than answers.

Stephen Deedes-Vincke says he has seen almost none of the insects in North Vancouver's hub, known as Butterflyway Lane.

As a "butterfly way ranger" with the David Suzuki Foundation's Butterflyway Project, his job is to help butterflies and bees thrive, but this year has been challenging.

"This year, I have seen about two or three, and normally, we'd see about 100, just in this little area. Anecdotally, this year has been really bad," Deedes-Vincke said.

On the iNaturalist website, which is dedicated to observing species, people can upload their photos of butterfly sightings. As of Friday, only 671 butterfly sightings have been recorded in Metro Vancouver since March. In 2023, the number was over 1,500 over the same period.

The Butterflyway Project helps butterflies thrive by encouraging people to grow native and pollinator plants. In Butterflyway Lane, located in the east of North Vancouver, 21 neighbours have collaborated to help butterflies survive.

A butterfly will land on a plant and continue its way down the "lane" to pollinate the others. They will also lay eggs on what Deedes-Vincke calls "host plants."

Over the six years he has been part of the project, Deedes-Vincke has seen butterfly numbers grow — until this year.

He thinks sudden changes in weather could be to blame because they can hurt caterpillars and butterflies, and also plants. Deedes-Vincke says many of his plants didn't survive after the spring.

"I think it's really the speed of change in temperature. One day, it could be freezing, and the next, it's so quick to suddenly change to heat, and then it might flip back to freezing," he said.

UBC botany and zoology professor Michelle Tseng thinks January's extreme cold snap could be one reason why butterfly sightings are low this year.

Temperatures dropped lower than -20 C on Jan. 11-15 in some areas of B.C. In Vancouver, it got as low as -12 C, but the Arctic wind chill made it feel much colder.

Metro Vancouver also experienced a wet, cool spring.

"We don't know for sure if the cold snap was absolutely due to climate change, but we do know that extreme weather events are more likely to happen with climate change," Tseng said.

Unpredictable weather can confuse caterpillars and butterflies when it comes to their time to hibernate and reproduce.

Tseng says the butterfly sighting numbers are concerning. She recently released a peer-reviewed study in the Canadian Journal of Zoology with other researchers that indicated planting more native trees in Vancouver could help.

They found native trees were associated with five times more native butterfly species than non-native trees.

Paper birch, Douglas fir and apple trees were some examples that carry most native B.C. butterflies and moths, according to the study.

"Native species of butterflies and moths really do need native species of plants in order to survive. What we're hoping to get people thinking about more is … the actual geographic origin of the tree we're planting in our cities," Tseng says.

She says as well as planting native trees, residents can help boost butterfly populations in other ways, like limiting the use of insecticides.

In the meantime, Tseng says she and others are completing further research on why butterfly numbers are down this year.

Deedes-Vincke hopes the butterflies return soon, noting their importance to local ecosystems through their work pollinating flowers and other plants.

"If the butterflies disappear, I think we've got a bigger problem," he said.