Stepping outside the confines of your home has become a blood sport. A late-summer scourge of mosquitoes has taken wing in Edmonton.
After a slow start to the season, city traps designed to capture trends in Edmonton’s mosquito population show they are now enjoying a late-season boom, with freshly-hatched hordes searching for their next blood meal.
At the city’s mosquito lab, Sarah McPike, a senior biological sciences technologist, opens plastic bins filled to the brim with so many specimens a distinctly foul stench wafts over the room.
It’s no surprise to her that some Edmontonians are feeling a bit itchy. McPike’s summer sampling has revealed a bumper crop.
Last year in the third week of August the city’s carbon dioxide-baited traps captured about 600 mosquitoes. This past week, more than 42,000 mosquitoes were caught.
“It’s quite a staggering increase,” McPike said. “There’s a lot of reasons why this might be happening but we did have the perfect storm.”
Sarah McPike with some water she collected, filled with hundreds of mosquito larvae and pupae. City traps have been inundated with species of the pesky insects. (Kory Siegers/CBC )
Heavy rains in recent weeks have made Edmonton an ideal breeding ground, with rainwater filling up ditches, potholes and stormwater sloughs, McPike said.
Most mosquitoes in the Edmonton area are floodwater species; females lay eggs in the vegetation around ditches and other temporary water bodies.
When heavy rain falls, the eggs become submerged and are “activated,” she said.
Within a week or so, newly hatched females are ready to bite.
The great tormentor
Among the roughly 30 mosquito species that pester Edmontonians, Aedes vexans remains the most common. Its name, vexans, comes from the Latin word for torment — and it lives up to its billing, with a reputation as an aggressive daytime biter.
There is, however, a new pest on the scene. Numbers of Culex pipiens have shot up, contributing to the overall population boom, McPike said.
The mosquito, unseen in Edmonton until 2019, is a known carrier of West Nile virus, which can cause a fatal neurological disease in birds and other animals, including humans.
Also known as the common house mosquito, Culex pipiens loves urban environments, often laying its eggs in the stagnant water of old rain barrels, discarded tires or neglected bird baths.
The city is monitoring its numbers, tracking any increases in West Nile cases, and exploring at expanded treatment options for breeding grounds, including the city’s more than 60,000 stormwater catch basins, McPike said.
“Culex pipiens, it has changed our game because they’re developing in the stormwater catch basins and they overwinter as adults,” she said. “Last year, we were dipping in our catch basins and finding larvae in them all the way through October.
“We haven’t seen an increase in West Nile activity in the Edmonton area so far. But we will be watching for that.”
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The first evidence of the virus in Alberta was confirmed in July 2003. Between 2003 and 2021, 541 human cases of West Nile virus were detected in the province, many of which were acquired in Alberta.
McPike says that as temperatures cool, daytime biters should become less aggressive before the frost eventually kills them off.
In the meantime, she encourages Edmontonians to cover up, wear bug spray and keep their yards clear of standing water.
It’s unclear why the house mosquito has moved into Edmonton but researchers suspect climate change has expanded its territory north, said John Swann, an entomologist with the University of Calgary.
He characterizes the changing weather patterns as a mixed bag for mosquitoes.
Milder temperatures, especially in winter, have given some species an edge, just as drought-like conditions can curtail the breeding season for others.
Swann described Edmonton as prime mosquito territory and said numbers in the capital are elevated compared to Calgary and other cities in southern Alberta.
As drought conditions persist across the West, he urges any Edmontonians bothered by mosquitoes this month to put their plight in context.
“It’s probably a small price to pay for some moisture.”
What lies beneath? Mosquito larvae float in a beaker at Edmonton’s monitoring lab. Most species in Edmonton rely on heavy rain to help hatch their young. (David Bajer/CBC)
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