Alien species are plants or animals that don't originate from an area where they are now established. Usually, these uninvited visitors arrive in Canada as a direct or indirect result of human activities. Some come aboard freighters, mixed up in livestock feed or in ships' ballast tanks. Others hitch rides on trucks and freight trains, or are deliberately introduced by humans for profit or pleasure. Many aliens quietly take up residence and cause no problems. A few, however, spread rapidly and crowd out native species.
The European starling, which came to North America 100 years ago, has taken over many of the nesting sites of native species like the eastern bluebird. The European earwig is another example of an unwelcome guest in Canadian gardens. The gypsy moth was brought to the United States in 1869 by a French entrepreneur who planned to start a silkworm industry. The plan failed, but the gypsy moth flourished. Within two decades, the moths and their larvae were serious pests. The species arrived in Ontario in the 1970s, and by 1985 they had spread throughout the province.
Another less typical example of an exotic invasion has occurred on British Columbia's Queen Charlotte Islands. Here, the sea birds are disappearing at an alarming rate. The culprits, as it happens, are raccoons. Over 50 years ago, eight were released here for the benefit of local trappers. Unfortunately, these furry bandits are exceedingly fond of gobbling up the eggs and chicks of ground-nesting birds. Currently, there are so many raccoons that they could wipe out the entire bird population of the islands.
Among the most recent exotic troublemakers in Canada are zebra mussels and purple loosestrife. Both probably came to North America from Europe. For advice on dealing with these intruders, see "Curb the Spread of Zebra Mussels" and "Root out Purple Loosestrife".
Are unwanted visitors making life difficult for native species in your area? If so you may be able to curb the invasion, or help bring ousted wildlife back home again. Take the case of one exiled songbird: when the European starling elbowed out the eastern bluebird in the battle for nesting cavities, bluebird numbers dropped sharply. However, a campaign to erect artificial bluebird boxes has eased the housing crisis, and the species is making an encouraging comeback.
For more information on exotic invaders and how to combat them, contact your provincial or territorial branch of Natural Resources Canada.