Quirks and Quarks

Have species from Canada invaded other places?

Canada experiences problems with invasive species but some native Canadian species are causing problems in other countries.
A woman feeds a grey squirrel in London, England where they have become an invasive species driving the native red squirrel to extinction through competition and disease. (Dan Kitwood/Getty Images)

This week's question comes from Alex Martin from Greensville, Ont. He asks:

We hear a lot about invasive species to Canada, my question is whether it's reciprocal, that is, do we tend to export as many invasive species as we seem to import? If not, why is there a disparity?

Anthony Ricciardi, a professor at the School of Environment at McGill University in Montreal, Que., says that though a huge number of species that have invaded other countries, very few have come from Canada.

One example is the Pacific oyster, which was brought to Europe from B.C. to establish oyster farms but has now overgrown in some places and smothers native mussel beds. This species, however, didn't originate in Canada, it was originally brought from Japan to B.C. in the early 1900's.

There are a number of species native to North America that have caused invasive species problems abroad, but it's not clear if the invading populations came from Canada or the United States. Some examples are the bullfrog, the grey squirrel, the beaver, several fresh water fish and various plants, including goldenrod. The grey squirrel was introduced for sport hunting in the United Kingdom but it's now driving the native red squirrel to extinction through competition and disease.