Key Takeaways
- Health Canada advises keeping ant baits available for at least two weeks.Source: Health Canada, Ants (Pest control tips) (June 2017)
- Where European fire ants had moved in, they made up more than 99.99% of all ants caught in traps in a British Columbia study.Source: The Canadian Entomologist (Naumann and Higgins), The European fire ant (Hymenoptera: Formicidae) as an invasive species: impact on local ant species and other epigaeic arthropods (December 2014)
- Odorous house ant supercolonies in cities can hold millions of workers and thousands of queens, a 2023 study reports.Source: Scientific Reports (Buczkowski et al.), Behavioral assays reveal mechanisms of supercolony formation in odorous house ants (June 2023)
- A 2010 review of pharaoh ant records from more than 1,200 sites says the species is particularly notorious as a pest in hospitals.Source: Myrmecological News (Wetterer JK), Worldwide spread of the pharaoh ant, Monomorium pharaonis (Hymenoptera: Formicidae) (March 2010)
- The earliest known Ontario record of the pharaoh ant dates to 1880, according to a 2010 worldwide review.Source: Myrmecological News (Wetterer JK), Worldwide spread of the pharaoh ant, Monomorium pharaonis (Hymenoptera: Formicidae) (March 2010)
Are new ant species moving into Ontario?
Some are: the European fire ant, an invasive species, has become increasingly abundant in eastern North America, including southern Ontario, according to the University of Toronto. The ants in Ontario are changing, and homeowners and pest control techs both need to be able to tell them apart, since some of them need a different treatment.
What is an odorous house ant and why is it hard to get rid of?
It's a widespread ant (Tapinoma sessile) native to North America whose city supercolonies can hold millions of workers and thousands of queens, so control takes bait and patience. Health Canada lists it among the ants known to invade homes in Canada. It gets its name from the odour it gives off when crushed, most often described as rotten coconut.
Researchers in a 2023 study describe the species as a challenging urban pest. Bait has to go directly in the path of foraging ants, and Health Canada advises keeping baits available for at least two weeks and says repeat applications may be needed.
Are European fire ants in Ontario, and do they sting?
Yes: the European fire ant (Myrmica rubra) is invading southern Ontario gardens, yards, parks and forests, and its colonies can deliver a painful sting, according to the University of Toronto. European fire ant colonies can be aggressive, and in a British Columbia study their populations were linked to fewer other ant species, so where they show up, they need to be dealt with first.
Pavement ants are a different case: Health Canada says they can become a nuisance in lawns, gardens and pathways, as well as indoors.
Why can spraying pharaoh ants indoors make things worse?
Because spraying can split the colony: Health Canada warns that, with any indoor ant nest, spraying where trails are seen may cut off the nest's food and water and encourage the colony to split into multiple new colonies. Pharaoh ants appear to have originated in tropical Asia; in temperate places like Ontario they are found almost only indoors, and they are particularly notorious as a pest in hospitals. They need a specific treatment.
Why do you need to identify ants before treating them?
Because the few ants you see are often the edge of a big colony, and you have to know which ant it is and how that colony is set up before you can deal with it. If ants keep coming back and the usual treatment isn't working, start by having a professional identify them.
Sources
- Health Canada: Ants (Pest control tips)
- University of Toronto: European fire ants team up with invasive plant species
- The Canadian Entomologist (Naumann and Higgins): The European fire ant (Hymenoptera: Formicidae) as an invasive species: impact on local ant species and other epigaeic arthropods
- Scientific Reports (Buczkowski et al.): Behavioral assays reveal mechanisms of supercolony formation in odorous house ants
- American Entomologist (Penick and Smith): The True Odor of the Odorous House Ant
- Myrmecological News (Wetterer JK): Worldwide spread of the pharaoh ant, Monomorium pharaonis (Hymenoptera: Formicidae)
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Sting Out Pest Control. (2026, October 17). New Ant Species Moving Into Ontario. https://www.stingoutpestcontrol.com/blog/new-ant-species-ontario
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