10 Most Dangerous Invasive Species in Ontario

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Nature is a wonderful thing. Our planet’s biodiversity is unparalleled in the universe (at least, as far as our knowledge goes), and this means that every region has its own unique plants and animals.

However, due to human movement, whether intentional or otherwise, invasive species end up in another region’s environment and cause harm to that region’s native species.

Let’s take a look at the invasive species in Ontario, Canada.

1. Ten Invasive Species in Ontario

1.1 Asian Carp

The term “Asian Carp” describes four species of carp that are indigenous to the lakes, rivers, and reservoirs of southern Russia and China.

Due to their unique diets, they were brought to the Southern United States for use as biological controls in aquaculture facilities.

1.2 Zebra Mussels and Quagga Mussels

invasive species in ontario
Photo by CHUTTERSNAP on Unsplash/Copyright 2018

Zebra and Quagga Mussels are freshwater mollusks, indigenous to the Black Sea region of Eurasia. Both species were thought to have arrived through transoceanic ships’ ballast water.

Quagga Mussels are only found in the southern Great Lakes, specifically Lakes Ontario, Michigan, Huron, and Erie.


  1. These invasive mussels remove plankton from the water, and native species no longer have access to it as a food source.
  2. Large colonies may encroach on beaches and fish-hatching grounds, slashing swimmers’ feet.
  3. Due to their large colonies, they also obstruct water intake lines.
  4. They can increase toxic algal blooms, which lowers the quality of the water and adversely impacts native fish and aquatic wildlife.
  5. They are easily transferred throughout bodies of water and latch onto boats.

1.3 Phragmites

by huggy1/DepositPhotos

Also called the European Common Reed, these aggressive phragmites outcompete native species for water and nutrients and spread swiftly. Its roots exude biochemicals into the soil, preventing neighbouring plants from growing.

Invasive phragmites typically grow up to 5 meters tall.


  1. They lower plant biodiversity as a result of natural plants being crowded out, as they can grow so densely that it crowds out other species.
  2. It offers limited habitat and food resources to the general wildlife, thus causing issues within the region’s food chain.
  3. They cause lower water levels resulting from rapid growth because they shed moisture more quickly than native plants would.
  4. It increases fire risks since the reed stands contain a large number of dead stalks.
  5. They can adversely influence agriculture, provide a risk to traffic safety, and have an effect on leisure activities like swimming, boating, and fishing.

1.4 Water Soldier

This is a submerged, perennial, invasive aquatic plant, and it is believed that vegetative reproduction is the main method of dissemination in North America.


  1. Water soldiers can be underwater up to 5 meters, but during the summer they float to the surface. Summertime pastimes like swimming, boating, and fishing are put in danger by this.
  2. They create stagnant waterways by forming dense floating vegetation mats, which also reduced biodiversity by displacing indigenous aquatic species.
  3. They also can change the chemical of the nearby water, which could hurt phytoplankton and other significant aquatic creatures.
  4. Swimmers and anybody who touches these plants risk getting hurt by the plants’ sharp, serrated leaf edges. So, be careful handling them if you do happen to come across them.

1.5 Purple Loosestrife

invasive species in ontario
Photo by Liana Mikah on Unsplash/Copyright 2018

Nearly every province of Canada and practically every state in the United States now have Purple Loosestrife, which has spread quickly throughout the continent.


  1. It can produce up to two million seeds in a single growing season, resulting in dense stands that outcompete natural plants for habitat.
  2. Due to these populations, ecosystem services are altered, which includes fewer places for birds to nest, shelter, and food, as well as a general reduction in biodiversity.
  3. Large patches of this plant can ruin farmland, obstruct irrigation channels, and lower the fodder value of pastures.

1.6 Dog Strangling Vine

Black Swallow-Wort and Pale Swallow-Wort, two invasive plants that are native to Eurasia, are both referred to as “Dog-Strangling Vines.” These perennial vines have been aggressively colonizing central and southern Ontario in recent years.


  1. This vine aggressively spreads by draping itself along the ground or wrapping itself around other plants and trees causing them to become “strangled” by dense vine patches.
  2. It grows into dense stands that suffocate and choke out new trees and other plants, hindering the regeneration of forests.
  3. It is challenging to eradicate because the seeds are quickly dispersed by the wind and new plants can arise from root pieces.
  4. Colonies create mats of intertwined vines that are difficult to navigate and obstruct recreational activities in the forest.
  5. Livestock may be poisoned by leaves and roots. Deer and other animals avoid it as well, putting less desirable native plants under increased grazing strain.
  6. The monarch butterfly, a species in danger in Ontario, is in danger from the vine. The butterflies lay their eggs on it, but the larvae cannot finish their life cycle and die.

1.7 European Buckthorn

invasive species in ontario
Photo by Yulia Khlebnikova on Unsplash/Copyright 2020

European Buckthorn, also known as Common Buckthorn, is a native of Europe. It was frequently planted for fencerows and windbreaks in agricultural areas after being brought to North America as an ornamental shrub.

Since then it has spread rapidly. It can be found throughout Canada, from Saskatchewan to Nova Scotia.


  1. It outcompetes native plants, lowers biodiversity, degrades the quality of wildlife habitats, and negatively impacts a variety of industries and the environment.
  2. It grows in thickets that push out native species.
  3. It can change the amount of nitrogen in the soil, improving circumstances for its own growth and inhibiting the growth of native species.
  4. It produces a lot of seeds, many of which germinate quickly and stop the growth of local trees and plants.

1.8 Giant Hogweed

A member of the carrot family, the Giant Hogweed is grown for decorative purposes in gardens. It can grow in ditches, streams, and roadside edges and is spreading across North America and is becoming more prevalent in southern and central Ontario.


  1. Giant hogweed possesses a toxic sap that can severely burn human skin when exposed to light. Blisters that hurt appear within 48 hours as symptoms. Purple scars can develop and remain for years.
  2. Because of this, removal can be risky; therefore, it shouldn’t be composted or burned.

Pulling giant hogweed when it is still very young and small and storing all plant parts in sealed black rubbish bags until the plant is dried and the seeds are no longer viable are the simplest ways to get rid of it. Garden gigantic hogweed should not be planted, and sightings should be reported.

1.9 Emerald Ash Borer

Emerald Ash Borer
by yod67/DepositPhotos

An invasive wood-boring beetle that is native to areas of Asia is called the emerald ash borer (EAB). It has been found in the Detroit, Michigan, and Windsor, Ontario, regions.


  1. Millions of Ash trees in southwest Ontario and the Great Lakes States have been devastated by this forest pest, causing the loss of expensive wood that is used to make furniture, buildings, and leisure products.
  2. When its larvae burrow through a tree’s vascular system, which distributes water, nutrients, and sugars throughout the tree, it kills Ash trees.
  3. There are no known natural enemies that limit population growth or spread, and it causes loss of food sources and habitat for other animals.

The Canadian Food Inspection Agency has declared it illegal to move firewood and any other items made from Ash trees outside of the areas that have been classified as Infested Places Orders due to the significant economic and environmental damage they pose.

1.10 Beech Bark Disease

A new hazard to beech (Fagus grandifolia) trees in Canada’s hardwood and mixed forests is beech bark disease or the beech leaf disease which was first identified in North America.

Since then, it has rapidly spread and is currently present in several American states as well as Ontario.

An imported European beech scale insect and the nectria fungus work together to create this illness.


  1. Beech bark disease causes older beech trees to severely die back, potentially posing a serious danger to Ontario’s wildlife, biodiversity, and sustainable forestry.
  2. It reduces the number of trees that provide food to wildlife. Beechnuts are a crucial source of food for wildlife, particularly for black bears.
  3. It seriously weakens trees, putting them at risk of additional challenges.
  4. It decreases the use or marketability of wood products.

While the majestic beech stands of Ontario are seriously threatened by this new disease, not all beech are affected, and individual beech tree prevention is achievable.

2. Frequently Asked Questions (FAQs)

2.1 What are Invasive Species?

Invasive species refers to any plants, animals, or other organisms that are not native to an ecosystem and that cause harm to the environment, the economy, or human health.

2.2 How Many Types of Invasive Species in Ontario Are There?

Invasive species in Ontario can be broadly divided into 5 categories.

2.3 What Is the Most Invasive Species in Ontario?

Depending on the region, the answer to this will differ, making it a very subjective question. Overall, the Asian Carp can be considered the most aquatic invasive species in Ontario, and the Emerald ash borer is one of the most invasive species in Ontario, forest pests.

2.4 How Can These Invasive Species in Ontario Be Managed?

Managing invasive species in Ontario that have already established themselves is difficult, but some steps can be taken. To help stop the spread of aquatic invaders, make sure that any vegetation, animals, and dirt are removed from boats and trailers before leaving a location.

Avoid boating through infected areas, clean any sporting goods, and never release or compost unwanted aquarium plants to stop the spread of this disease. Find out more here.

2.5 What Steps Is the Government Taking to Control Invasive Species in Ontario?

The Invasive Species Act, which clearly governs the prevention and management of invasive species in Ontario, was introduced by the provincial government of Ontario in 2015. This Act created two categories – prohibited and restricted. Initially, there were 22 prohibited and 11 restricted invasive species. In January 2022, 13 new invasive species were added.

3. Closing Notes

Invasive species in Ontario have travelled here from great distances, and are causing huge amounts of damage to the native wildlife habitats and the ecosystems of this region.

It is important to be careful during outdoor activities, to prevent spreading them through human action, especially during water activities, and hiking. Clean and dry boats and shoes, and make sure to check and clean the fur of your pets.

Learning to identify this species so that you can report it to the authorities will make all the difference.

Muskaan grew up with her nose always buried in a book, and that love of reading has now spilled over into a love of writing. She also has a passion for traveling and enjoys sharing her experiences. Her research skills as a law student have come in handy when planning adventures. Muskaan is dedicated to delivering high-quality content that informs and entertains and is always looking for new and exciting writing opportunities.