Record Rain Fuels Mosquito Surge Across Canada

Experts point to the record rainfall that fell across southern Ontario this summer as a likely cause of the unusually large mosquito numbers that are still being reported in September. Fiona Hunter, a medical and veterinary entomology professor at Brock University, noted that the flood‑water mosquito Ochlerotatus trivittatus has been especially abundant.

Ochlerotatus trivittatus is a flood‑water species that deposits its eggs in low‑lying, water‑filled spots such as soggy fields, lawn depressions and roadside ditches. The recent rain created exactly those habitats, allowing the species to lay more eggs.

In Edmonton, the city’s monitoring showed mosquito counts in July were about 15 times higher than at the same time last year. Peter Daly, a biological sciences technologist at the City of Edmonton, said the figures represent a stark contrast to the previous two summers, even if they are not a regional record.

Cities in the Prairies – including locations in Manitoba, Saskatchewan and Alberta – also reported an early‑season surge. Stores that sell insect repellent ran out of stock as residents scrambled for protection.

Rosalind Murray, an assistant professor of biology at the University of Toronto, explained that the heavy downpours may have triggered the hatching of dormant mosquito eggs, creating a temporary “boom” in areas that experienced major flooding, such as Toronto.

The combination of more breeding sites and the possible hatching of dormant eggs means mosquitoes can stay active longer and bite more often, which may be part of the reason people feel they are being bitten more this summer.

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