Navigating Nature: Identifying 9 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), which means that every region has 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.

1. Top 9 Invasive Species in Ontario

1.1 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 the ballast water of transoceanic ships.

Quagga Mussels have spread beyond the southern Great Lakes and can be found in various parts of the United States, including Texas, Colorado, Utah, Nevada, and California.


  1. These invasive mussels remove plankton from the water, and native species can no longer access 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, lowering the water quality and adversely impacting native fish and aquatic wildlife.

1.2 Phragmites

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 neighboring plants from growing.

Invasive phragmites typically grow up to 5 meters tall.


  1. They lower plant biodiversity due to natural plants being crowded out, as they can grow so densely that they crowd 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 many dead stalks.
  5. They can adversely influence agriculture, risk traffic safety, and affect leisure activities like swimming, boating, and fishing.

1.3 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 they float to the surface during the summer. This puts summertime pastimes like swimming, boating, and fishing in danger.
  2. They create stagnant waterways by forming dense floating vegetation mats, reducing 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 come across them.

1.4 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 has 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.

1.5 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 recently.


  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 wind quickly disperses the seeds, 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. Leaves and roots may poison livestock. Deer and other animals also avoid it, 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.

1.6 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 various 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 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.

1.7 Giant Hogweed

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


  1. When exposed to light, giant hogweed possesses a toxic sap that can severely burn human skin. 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 can be done, but it carries a high risk due to the plant’s sap, which can cause severe burns when exposed to sunlight. Therefore, using herbicides and seeking professional help to control giant hogweed is recommended.

Garden gigantic hogweed should not be planted, and sightings should be reported.

1.8 Emerald Ash Borer

An invasive wood-boring beetle native to areas of Asia is called the Emerald Ash Borer (EAB). It has been found in Detroit, Michigan, and Windsor, Ontario.


  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 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. Some known natural enemies, such as wasps and bark-foraging birds, may limit population growth or spread and cause 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 classified as Infested Places Orders due to the significant economic and environmental damage they pose.

1.9 Beech Bark Disease

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

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

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


  1. Beech bark disease causes older beech trees to die, potentially harming Ontario’s wildlife, biodiversity, and sustainable forestry.
  2. It reduces the number of trees that provide food to wildlife. Beechnuts are a crucial food source for wildlife, particularly for black bears.
  3. It seriously weakens trees, putting them at risk of additional challenges.

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

In Pursuit of Invasive Species: Ontario Forests

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 cause harm to the environment, the economy, or human health.

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

Ontario has the most invasive species in Canada – more than 180 aquatic invasive species, approximately 500 non-native plants, 39 known forest insects, and ten tree diseases.

2.3 What Is the Most Invasive Species in Ontario?

Depending on the region, the answer will differ, making it a very subjective question.

2.4 How Can These Invasive Species Be Managed?

Managing invasive species that have already established themselves is difficult, but some steps can be taken. To help stop the spread of aquatic invaders, remove any vegetation, animals, and dirt 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 governs the prevention and management of invasive species in Ontario, was introduced by Ontario’s provincial government 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 traveled 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 check and clean your pets’ fur.

Identifying this species so you can report it to the authorities will make all the difference.

Last Updated on by Ananya Sreen

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