Invasive ants currently found only indoors in cooler regions such as Canada could soon begin to spread outdoors as global temperatures rise, according to a new study from the University of Toronto.
These ants typically enter Canadian buildings after hitching rides in shipping crates, plant pots, soil and nearly any crack or crevice - and then are transported between regions along with consumer goods.
Researchers, whose findings were published in the journal Diversity and Distributions , warn that some invasive ant species could cause significant damage if they become established outdoors.
"We tend to think of non-native species invading outdoor environments only," says Toby Tsang, a postdoctoral researcher in the department of biological sciences at U of T Scarborough and lead author of the study.
"But indoor environments - like homes, buildings and greenhouses - can act as safe havens for non-native ants, especially in colder regions where they wouldn't normally be able to survive outside."
Tsang analyzed global data on 323 non-native ant species across 477 distinct geographical regions to examine how climate conditions affect whether ants remain indoors or can spread outdoors. His model found that with 2 C to 4 C of global warming, ants currently confined to indoor environments are more likely to establish themselves outside, particularly in the colder parts of the Northern Hemisphere.
He says that indoor environments can serve as a "stepping stone" for ant invasions, offering a warm, safe place to live until outdoor conditions become more favourable.
Invasive ants introduced into buildings or greenhouses can be difficult to detect due to their small size, allowing populations to grow unnoticed.
"Many ants have a broad diet, so food isn't a problem," says Tsang. "Indoor environments also lack large predators of ants. Once a nest is established, indoor environments provide a safe place where ants can thrive."
In Ontario, there are currently five species of non-native ants that can only be found living indoors - and one of them poses a potential to cause significant damage if it spreads outdoors.
Wasmannia auropunctata, commonly known as the electric ant or little fire ant, is a small golden brown species native to Central and South America that derives its name from a painful sting relative to its size. It has spread outdoors in five continents, including North America, and is currently living inside greenhouses in various parts of Canada.
Listed as one of the world's top 100 worst invasive species by the International Union for Conservation of Nature , Wasmannia auropunctata can outcompete native ants and prey on other insects and even small animals. It's also an agricultural pest, known to attack farm workers and animals - its sting can cause blindness in severe cases. These ants also contribute to crop damage by protecting pests such as aphids from predators in exchange for honeydew, a key food source.
Despite the risks posed by ants like Wasmannia auropunctata, Tsang says invasion monitoring programs often overlook indoor populations of non-native species.
"Some of the ants that are most likely to spread can be very harmful, such as the Argentine ant and Wasmannia," says Tsang, whose research focuses on how climate change might contribute to ant invasions.
"These species can outcompete and prey on native species, cause ecological and agricultural damage, and even pose health risks to humans. We need to pay better attention to them."
