Blame it on the rain: Record downpour in Edmonton will bring monsoon of mosquitoes

Already itchy? Recent heavy rains in Edmonton have triggered a monsoon of mosquitoes that will soon be out for blood.

After a month of record rain in the capital region, freshly-hatched hordes will soon be taking wing across the capital region.

Mike Jenkins, a senior scientist and pest management coordinator with the City of Edmonton, said local populations of mosquitoes during this spring were already the highest the city has seen in several years.

Heavy rains in early June, paired with a severe deluge over the past weekend, means their numbers are expected to explode, he said.

“The ground is pretty saturated and that water is not going to go anywhere very quickly,” Jenkins said. “It's going to form those temporary habitats the mosquitoes can use to develop large numbers.

“We could end up with a couple of different generations of mosquitoes overlapping each other.”

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In Edmonton, years of drought means many years-worth of eggs that have lain dormant during summer dry spells are now springing to life, Jenkins said.

Female mosquitoes lay their eggs in moist soil or standing water. Depending on the species, they will hatch within days or lay in wait for the perfect flooding conditions before they are “activated” and begin to hatch, Jenkins said.

Within a week or so, the females who have hatched will be ready to draw blood. That means more rain will bring more mosquitoes, and the bugs are in for a banner, blood-sucking summer.

“They can lay dormant in some cases for up to a decade until they're actually activated by that precipitation,” he said. “And so they've been waiting, they've been inundated and now have been activated.”

The good news? It could have been a lot worse.

Dry weather in recent years and a particularly parched early spring had kept mosquito numbers relatively low compared to what would be expected, Jenkins said.

The number of viable dormant eggs is relatively low due years of dry summers that have left mosquito egg banks depleted, meaning the resulting hatch has remained relatively small for the amount of standing water on the ground.

The trend won’t hold though, Jenkins said. Within a week or so after the rains, the city’s cup will be running over with mosquitoes.

“But now, those mosquitoes that have been activated by the rainfalls, they're collecting blood meals, and using the protein to lay more eggs,” Jenkins said.

“Going forward, that can ramp up really, really quickly. And the dry years that we've had for a long period aren't going to be a benefit to us much longer.”

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City crews are out attempting to keep the population to a low buzz with targeted treatments in known hatching habitats, Jenkins said

These priority areas include roadside ditches along city freeways and swampy areas near busy parks and trails where mosquitoes prove to be a particular nuisance.

He said the treatments used by the city only last so long and with “continual inundations” of new eggs and fresh hatchlings that have developed into larvae, the timing of the city's attacks is critical.

The city’s CO2-baited mosquito traps indicate that their numbers have already begun to climb.

In the week of June 8, each trap captured an average of 289 mosquitoes. Over the course of last week, that number exploded by over 1,200 per cent, to an average of 3,753 mosquitoes per trap.

Jenkins encourages Edmontonians eager to avoid the itch to cover up and remove any standing water from their properties.

This advice has become particularly important due to the arrival of a relatively new species in the Edmonton region, Jenkins said. Known as Culex pipiens, it’s a known carrier of the West Nile virus, which can cause a fatal neurological disease in birds and other animals, including humans.

It was first identified in Edmonton in 2018, and has subsequently migrated to Calgary and across southern Alberta.

Unlike many floodwater mosquitoes native to the region, this species prefers to lay its eggs in standing water, Jenkins said. Forgotten watering cans or neglected bird baths can quickly become a breeding ground.

Ilan Domnich, an Alberta-based entomologist, said the city's program aims to kill larvae before they hatch, but only targets certain species known to carry diseases. The program relies on biological larvicides rather than spraying for adult bugs.

"Not only can they bite us and cause these, you know, itchy, annoying welts, but of course some mosquitoes can also transmit diseases," Domnich said in a recent interview.

"That is actually the main reason that we control our mosquito population."

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Jenkins said the risk of disease transmission is a concern but notes research has shown that the bugs prefer to bite birds, not humans.

Of Edmonton’s roughly 30 mosquito species, the Aedes vexans remains Edmonton’s most notorious and common summertime pest and is expected to keep that mantle this summer.

Jenkins has the bites to prove it.

“The mosquitoes that are developing now are going to be almost entirely Aedes vexans,” he said.

“It's our typical summer dawn and dusk biter, a little stealthy ankle-biter.”