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Aliens Among Us

ConservationIssue 1NatureNature Issue 1

Contrary to popular belief, worms are not from Canada. They  are actually an invasive species. The worm was imported to Canada inadvertently and released into the natural environment.  Until recently, we thought we understood the role of  worms in the environment.Recent studies have shown that worms directly impact the environment in more ways than imagined, including which plant seeds will germinate and thrive.

But, in elementary school, we learnt that earthworms benefit the soil. Worms chew up decaying organics, and mix and fertilize the soil. Worms serve an important ecological function for healthy gardens and agriculture. So how can it be that worms could injure the environment? Is everything we learnt in second grade a lie?


It is hard to believe, but earthworms are not Canadian species.  In Southern Ontario, our forests, prairies, soils and ecosystems evolved and developed without the presence and processes of earthworms.  For thousands of years, the forests in Halton Region flourished without earthworm company.  It is presumed that when European settlers arrived on the shores of the St. Lawrence River, in the mid-1800s, they brought earthworms with them. Ships traveling to North America filled their ballast with European rock and soil. Upon arrival the soil was dumped on the shore to adjust the ballast weight of the ship. Plants for crops and gardens were also floated over. Stowed away in these soils were earthworms and worm eggs.  Their release into the environment was also the release of new ecological processes in the feedback loop of nature. Over time, 19 different types of earthworms have been introduced to Ontario. These worms are scientifically described as Annelida, Clitellata and Oligochaeta.

From the location that earthworms are introduced into the environment, they expand their territorial range at a relatively slow rate. It is estimated that earthworms expand their territory by one kilometre every hundred years. This is likely part of the reason that it has taken us so long to discover  earthworms are having some negative effects on the environment. Most noteworthy in the earthworm’s negative impact is its effect on some forest plants that grow on the forest floor.  Anyone who walks in the forest regularly knows the sudden burst of yellow trout lilies or marsh marigolds, or the white explosion of Trilliums and Bloodroot. The earthworm is eating the layer of soil that these plants grow in. Have you ever noticed how some forest floors are covered in plants, while others have very few? As earthworms expand their range into the soils of forests, scientists have observed a decline in the number and variety of plants that grow on the forest floor. Yet, there’s evidence that some forest species benefit from fraternizing with earthworms. Jack-in-the-pulpit for example, grows just fine in forests where earthworms have mixed the soil layers.  Large-flowering trillium on the other hand, grows better when the thick layer of leaves is left to slowly decompose. Earthworms are impacting and changing the ecosystem right underneath our feet.

Keep Your Enemies Close

Conservation Halton is monitoring the presence of earthworms in our parks and conservation lands. Understanding how prolific earthworms are in Halton region will help inform decisions to keep our local forests healthy.

Monitoring earthworms

Additionally, Conservation Halton partners with researchers from the University of Waterloo to further our understanding of earthworms’ impacts on the health of our ecosystems. Researchers Heather Cray and Michael McTavish, from the University of Waterloo, assembled research plots in Conservation Halton’s Glenorchy Conservation Area. Cray and McTavish are studying the effects of earthworms’ behaviour on seeds. Earthworms (granivores, that is, seed eaters) eat seeds broadcasted onto the soil. It is hypothesized that the intestinal gut of worms and their digestion processes could affect the germination rates of seeds. Depending on the plant species, the time spent in the earthworm’s gut can increase or decrease the germination rates of those seeds and the growth of subsequent seedlings. Earthworms also move seeds from the soil surface to underground for future consumption. Depending on the seed and its germination requirements, this action could benefit the seed by protecting it from being eaten by birds or rodents or stop it from germinating if the seed is buried too deep. Cray and McTavish are studying earthworm’s effects on both native and non-native plant seeds. Preliminary studies show that common grass seed (non-native) spread onto soil containing worms has a lower germination rate than grass seed spread onto soil without worms. This is likely due to worms burying seed and/or eating it.  Out of the yard and into nature; a portion of the Glenorchy Conservation Area is being re-established as a prairie. Cray is using the research plots at Glenorchy to study the impacts of worm presence on commonly used methods to re-establish prairie ecosystems.

Strengthen your Troops  

Most Canadians think of Saskatchewan when they hear the word prairie. Blue skies and endless horizon. Most have never heard of prairies in Ontario. That’s because only 3% of the land that was originally prairie remains.  A significant part of Southern Ontario was once covered with “Tallgrass Prairie,” the unique variety of prairie that grows in Ontario. Tallgrass Prairies are beautiful ecosystems that are home to brightly coloured flowering plants, tall swaying grasses, fluttering butterflies and the buzz of pollinators. Unfortunately they are one of the most endangered ecosystem types in Canada. The research Cray is doing will help to protect and re-establish prairies in Ontario. By studying worms? Yes. Understanding which prairie seeds’ germination rates are negatively affected by earthworms will inform and alter the methods used to re-establish prairie plants. For example if is determined that the seeds of Black-eyed Susan (a meadow & prairie plant with beautiful yellow flowers) has a low germination rate after traveling through the gut of an earthworm, then restoration ecologists will change the method used to restore Black-eyed Susan in prairies. It is common practice to apply prairie seeds directly onto the soil to re-establish prairie plants. If a site has earthworms present in the soil, plugs of Black-eyed Susan, started in a nursery may be planted instead of applying seeds.

Drive them out!

This is a lot of research, couldn’t we just evict them? Worms can be collected and killed, however controlling this species on a large scale is very difficult, costly and time consuming. There are literally thousands upon millions of worms living in the soils. Researching their effects on our ecosystems will inform how imperative it is to control earthworms or remove them from the environment. The issue is complex, and the impacts are mixed. There are positive impacts, like soil fertilization; and there are negative impacts, like on plant growth.

“The Only Constant is Change -”― Heraclitus

So, do we work to terminate earthworms or do we  accept their presence, and work with them? In the case of prairies Cray suggests the latter.  We should learn, understand, adapt. All of our environments; work places, homes, schools, societal norms and culture is in a state of rapid change. To conserve smart, we need to learn more about the intricacies of this tangled ecological knot. If we flex our brains to see things differently, we could understand the earthworm and its role in ecosystem health in an informed light. Are there ways to embrace the earthworm without losing biodiversity? In the face of climate change could the worm provide ecosystem functions that make nature more resilient? The answers to these questions, are ours, to figure out.

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Last modified: July 14, 2016

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