A species of enormous rodent that looks somewhere between a beaver and a capybara has been declared the latest mammalian menace to Ontario — even though it hasn't arrived yet.

The Nutria, or Myocastor coypus (myocastor literally translates to 'mouse beaver'), is a large semi-aquatic rodent that has already wrought destruction across much of the southeastern United States, spread to the north, and is now looming just outside Ontario's doorstep.

These rodents are definitely on the larger side, typically growing from 4 to 9 kg in weight and as long as 60 cm.

They are easily distinguished from native large rodents like groundhogs and beavers by their distinctive yellow-orange teeth protruding from the mouth, and their hairless, rat-like tails. Nutria most closely resemble muskrats, though the former can be distinguished by their colourful incisors, larger size, and round tail.

While native to South America, a combination of human introduction through fur trading and farming and the animals' ability to quickly reproduce, the nutria's range now extends as far north as the Great Lakes.

There are no known established populations in Canada, but the nutria's proximity to Ontario's doorstep led to the province prohibiting and restricting the species under the Invasive Species Act as of Jan. 1.

The nutria, along with nine other species of fish and plants, are now illegal to import, possess, deposit, release, transport, propagate (breed/grow), buy, sell, lease or trade anywhere in the province.

"Invasive species damage our ecosystems, impact our ability to enjoy outdoor activities and harm our economy by threatening the forestry and agriculture sectors," said Graydon Smith, Minister of Natural Resources and Forestry. "That's why we are taking action to restrict these invasive species to protect Ontario's economy and ecosystems."

The province warns of potential impacts, noting the species' "burrowing and foraging behaviour impacts agricultural areas and increases flooding risks, spread parasites and disease to humans, pets and livestock, and can destroy coastal wetlands."

"Invasive species are one of the most significant threats to biodiversity and a major concern to Ontario's natural ecosystems," says Kyle Borrowman, the Nature Conservancy of Canada's Director of Habitat Restoration in Ontario.

"The NCC is pleased to see the designation of these additional species under the Invasive Species Act," said Borrowman, adding that the newly designated species include "several that are not known to currently exist in Canada but are a considerable risk to our natural ecosystems if introduced."

Sarah Rang, Executive Director of the Invasive Species Centre, applauds the new additions to the Act, saying, "This action will help protect Ontario's lakes, lands and forests from these species and avoid future ecological and economic costs."

Managing nutria populations has proven challenging in areas where their numbers are well-established. Multiple U.S. states have offered bounties for each nutria killed as a means of outsourcing population control to the public. States like Louisiana, where nutria have ravaged local ecosystems, even have widely available dog treats made with nutria meat on the market as the corpses of these rodents pour in.

A total of 42 species are now listed under Ontario's Invasive Species Act, more than any other province in Canada.