It is known as the plant that ate the South.
Now kudzu, a rapidly growing invasive vine that blankets the landscape in parts of the southern United States, is heading north toward Canada.
"It is on the move," said Rowan Sage, a professor of ecology and evolutionary biology at the University of Toronto. "It will grow over your house if you don't keep it under control."
Also known as the cancer of the vegetative world, kudzu suppresses and kills other plants, including tree seedlings and native plants. It can grow two metres a week in all directions, quickly covering abandoned cars, tractors, houses and even traffic tunnels.
It is not just ugly. It affects both air and water quality, contributing to the formation of ground-level ozone, which is a component of smog, Dr. Sage said. It also contributes to the buildup of nitrogen in rivers and lakes.
And it is hardly the only creepy organism on the prowl. Dr. Sage assessed the threat posed by "bioinvasives," species that have the potential to wreak havoc, even destroy ecosystems, should they move into Canada. He said global-warming heightens the chances of unwelcome invaders - everything from fire ants to Japanese honeysuckle - spreading north.
Dr. Sage said he wants to figure out how big a risk some of these potential immigrants pose. His work is funded by the Natural Sciences and Engineering Research Council, which recently awarded him an "accelerator" grant, an extra $120,000 over three years given to scientists deemed to be on the verge of a breakthrough.
At the moment, one of his prime targets is kudzu, which was imported to the southern United States from Japan and China in the late 1800s, promoted as a way to fight erosion. Since then, it has proliferated so much that, in Chattanooga, Tenn., municipal officials have hired goats to keep a traffic tunnel clear for cars.
And now it's crawling north - spotted in Illinois, Pennsylvania, Connecticut, Massachusetts and Oregon.
Dr. Sage even has a carefully monitored kudzu plantation on the roof of his building in downtown Toronto. It requires constant trimming; any clippings or leaves are killed in an autoclave.
"Everything that leaves our hands is dead," he said. "We don't want to be the source of the first Canadian kudzu."
Theoretically, the plant could arrive here in debris on a truck. But what would happen then? Would it thrive, start to take over?
He and his colleague, Heather Coiner, have determined kudzu will die in the winter only if temperatures dip below -16 Celsius.
They plugged that information into climate models and found that in 15 years, Canadians could be looking at their own "kudzuscapes."
Imports that bite and clog
At least kudzu doesn't bite.
Imported fire ants, carried from South America to Alabama on cargo ships in the 1930s, are in North Carolina and moving north. And Dr. Sage knows how much they can hurt - he was bitten by them many times when he was a professor at the University of Georgia in the early 1990s.
He is considering studying imported fire ants, but said he is worried about the logistics of breeding them here, not to mention the possibility of personal injury.
"If you want to know the feeling, go get a needle and heat it up red hot and jam it into your skin," he said. "That's what it is like. When you get a whole bunch of them, your leg feels like you accidentally stepped into a pile of hot coals, and it gets all swollen.
"The fun part begins the next day, when the pain subsides and you begin to itch. It is worse than a mosquito bite - about three times itchier."
While most Canadians can only imagine the torment of fire ants, we are all too familiar with the damage invasive species can cause.
Zebra mussels have damaged harbours, boats and power plants since they moved into the Great Lakes in the late 1980s.
Eurasian watermilfoil, an aggressive water weed, is clogging lakes in Ontario, Quebec and British Columbia, and can make it difficult to boat or swim. Once milfoil arrives - usually on the propeller of a visiting boat - there is no getting rid of it.
