Where invasive alien species are found


According to the World Conservation Union, invasive alien species are the second most significant threat to biodiversity, after habitat destruction. No single region of Canada is immune from the potential for invasive alien species and many, if not all ecosystems are already experiencing some impact.

In their new ecosystems, invasive alien species become predators, competitors, parasites, hybridizers, and diseases of our native and domesticated plants and animals. The impact of invasive alien species on native ecosystems, habitats and species is severe and often irreversible.

Dog-strangling vine
Golden star tunicate © Fisheries and Oceans Canada
Sirex wasp © David R. Lance, USDA APHIS PPQ, bugwood.org
Purple loosestrife © John D. Byrd, Mississippi State University, bugwood.org

In 2002, it was estimated that 24 percent of the species listed as “at risk” by the Committee on the Status of Endangered Wildlife could be threatened with extinction by invasive alien species. Some of the 90 native species on this list that are considered threatened by invasive alien species include ancient murrelets, island blue butterfly, golden paintbrush, tiger salamander, northern prairie skink, American chestnut, eastern flying squirrel and ginseng.

Similarly, in the Great Lakes, now home to more than 160 alien species, sea lamprey have been implicated in the extinction of the deepwater cisco, and zebra mussels have extirpated native mussels from some areas.

Clearly, invasive alien species are an increasingly important factor in the decline of native species in both aquatic and terrestrial ecosystems.

Invasive alien species in terrestrial environments

Many of Canada’s diverse terrestrial environments have been impacted by invasive alien species of plants, animals, insects and disease. Invasive alien species are most often found in or near urban areas, as well as throughout the settled landscape. Invasive alien species can also be found in many of Canada’s more remote regions including the arctic.

Here are just a few invasive alien species found in Canada’s terrestrial environments.

Asian long-horned beetle © Michael Bohne, USDA Forest Service, bugwood.org
Table 1: Invasive alien species in terrestrial environments
Name of species: Description:
Japanese Knotweed
  • Large perennial plant native to China, Japan and Korea
  • Fast growing - can grow 2 or more meters in one growing season
  • This plant spreads primarily from discarded plant material or soil containing plant material
  • Found in many urban centres across Canada, and along some roadsides in Nova Scotia
  • Dense thickets will exclude other vegetation
Norway Rat
  • A mammal species originally native to central Asia
  • A species that has followed human settlement patterns across all continents of the world
  • Prolific breeders
  • Can cause significant damage to crops, buildings, food stores
  • Poses a significant human health risk
  • Norway rats are found in every province except Alberta which has been waging an active campaign to keep them out for over 50 years
European Earwig
  • First noted in Newfoundland 1827 to 1835
  • Have since spread to all urban centres across Canada
  • Not directly harmful to humans
  • Nocturnal scavengers of decaying plant material, as well as leaves, flowers and fruit
  • Can become a significant pest of urban properties and may enter dwellings if populations are high enough
Butternut Canker
  • This disease is a serious threat to Butternut trees across its native range
  • Scientists are currently unsure of the origins of this fungus but hypothesize it was originally introduced from outside North America
  • Butternut is now a species at risk in Ontario
  • Cankers formed on stems and branches can cut off the movement of water and nutrients within the tree
  • Cankers on the main stem will most often kill the tree

Invasive alien species in aquatic environments

Many aquatic environments like rivers, lakes and oceans have been seriously impacted by invasive species. Whether these invaders were first released in ballast water discharged from a ship, or from fisherman emptying bait buckets containing non-native species, or even from people discarding unwanted aquarium plants and animals, the end result is the same: a new aquatic alien species that can upset the natural balance of the ecosystem in which they were released.

Zebra mussel © Randy Westbrooks, U.S. Geological Survey, bugwood.org

Here are just a few species currently found within Canadian waters:

Table 1: Aquatic invasive species in saltwater environments
Name of species: Description:
Green Crab
  • Also known as the "cockroach of the sea"
  • Was first introduced to the waters off Cape Cod over 100 years ago
  • It had spread to the waters of New Brunswick by the 1950’s and British Columbia in 1998
  • Occupies the same habitat as native crabs, clams, oysters, and mussels
  • Invasive tunicates or ‘sea squirts’ are a type of filter-feeding animal that grow on submerged stationary objects
  • There are five know invasive tunicate species affecting the aquaculture and fisheries of Canada’s east and west coasts
Table 2: Aquatic invasive species in freshwater environments
Name of species: Description:
Chinese mitten crab
  • This crab spends much of its lifecycle in fresh water environments
  • Canada has no native freshwater crab species
  • Although first discovered in Lake Erie in 1965, it has not been able to become established in the Great Lakes, probably due to its need for both fresh and saltwater environments when completing its lifecycle
  • This species does represent a significant threat to St. Lawrence River and its many tributaries
Zebra Mussel
  • First discovered in the Great Lakes around 1986
  • Have significantly change the nature of the lake bottom, affecting fish habitat and spawning
  • Mussel populations often dominate near shore zones changing natural process such as nutrient flow into deeper waters
  • Mussels also excrete nutrients creating an environment that may be linked to water quality problems, such as algal fouling on rocky shorelines, off-tastes in drinking water and lethal outbreaks of botulism in wildlife, especially during warm water periods

Round goby


  • Introduced to the St. Clair River in 1990 probably through ballast water from ships originating from southern Europe
  • Have since colonized all five Great Lakes
  • Have impacted native fish populations
  • In Ontario, it is illegal to possess living round goby or to use them as bait 
  • Can spawn more then once per year

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