Some ant species that can only survive indoors in cooler regions could begin to move outdoors due to climate change, according to a new U of T Scarborough study.
The study, published in the journal Diversity and Distributions , is among the first to show how global warming may increase the risk of invasive species by enabling indoor-dwelling insects to expand into outdoor environments.
Researchers warn that some of these indoor-only ant species have the potential to cause significant damage if they become established outdoors.
"We tend to think of non-native species invading outdoor environments only," says Toby Tsang, a postdoc 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 look at how climate conditions affect whether ants remain indoors or can spread outdoors. His model found that with 2ºC to 4ºC 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 indoor environments can act as a "stepping stone" for ant invasions, giving them a warm, safe place to live until outdoor conditions become more favourable. Tsang says the majority are introduced indoors unintentionally, hiding in shipping crates, plant pots, soil, and just about any crack or crevice, then are accidentally transported between regions alongside consumer goods.
Once the ants arrive inside a building or greenhouse, they can be hard to detect due to their small size and can easily survive indoors in colder regions. Indoor environments also have fewer ant predators and can provide more sources of food, further improving their chances at survival.
"Many ants have a broad diet, so food isn't a problem. Indoor environments also lack large predators of ants. Once a nest is established, indoor environments provide a safe place where ants can thrive," says Tsang.
There are already documented cases of non-native ants escaping from indoor environments. In Ontario, where there are currently five species of non-native ants that can only be found living indoors, one of them has the 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 ant 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 are living inside greenhouses in various parts of Canada.
This bug is listed as one of the world's top 100 worst invasive species by the International Union for Conservation of Nature, due to its ability to outcompete native ant species 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. The ants also contribute to crop damage by protecting pests such as aphids from predators in exchange for honeydew, an important food source for the ants.
Despite the risk ants like Wasmannia auropunctata pose, Tsang says invasion monitoring programs tend to 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."
