Canada is being overrun by invasive ‘alien’ earthworms

While earthworms are generally praised for their beneficial roles in ecosystem functioning and agriculture, the invasion of non-native earthworms across Canada is starting to pose a significant threat to the country’s habitats. 

A new Stanford University study reveals that the proportion of alien earthworms in Canada is three times greater than native earthworms, with at least 70 different species of “alien” earthworms found in North America. 

Research also found alien earthworm species in 97 per cent of studied soils across North America, with the intruders accounting for 23 per cent of the continent’s 308 earthworm species. Not to mention, the pesky invasive species are also at an advantage, all thanks to their female’s ability to reproduce without fertilization from a male.

“These ratios are likely to increase because human activities facilitate the development of alien species that threaten native earthworm species, a phenomenon still largely overlooked,” said the study’s lead author, Jérôme Mathieu. 

According to, the introduction of invasive earthworms to the continent dates back to the late 1800s, with the practice aiming to exploit the species’ contributions to soil health. 

The squirmy creatures aerate the soil, promote drainage, facilitate water and nutrition penetration, and draw organic material into their burrow, accelerating the decomposition of organic matter and producing nutritive materials for growing plants. 

However, “alien” earthworms have now begun to stress native plants in Canada by altering the soil and encouraging the spread of invasive plant species. In North America, the species have stressed trees like sugar maples, triggering a series of impacts on the continent’s food web. 

Native species also face substantial threats from human activities, through the use of pesticides and habitat destruction. 

“It is a story of global homogenization of biodiversity by humans, which often leads to the decline of unique local species and the disruption of native ecosystem processes,” said study author professor Elizabeth Hadly. 

Unfortunately, these “alien” species aren’t the only worms causing issues in Canada. Another species, known as Bipalium adventitium, is similarly threatening havoc on local garden ecosystems, and has been spotted throughout the GTA over the past few years. 

Once the species finds its prey — which are usually unsuspecting earthworms, slugs, or insect larvae — it wraps its body around the victim and stabs it with an everted pharynx. 

Asian pheretimoid worms, or Amynthas, are also a relatively new species on the invasive list for Ontario. The creatures often cluster together in masses that include as many as 100 worms per square metre, posing a significant risk of causing ecological damage. 

Canada is being overrun by invasive ‘alien’ earthworms

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