Learning to live with invasive earthworms

When restoration is impossible, how do we move forward?

Earthworms are usually a welcome addition to any garden or field. They can increase the amount of air and water in the soil and help break down dead organic matter. But 19 of Canada’s 27 earthworm species are European imports. When they enter a new ecosystem, things start to change, literally from the ground up.

“Wherever they go, they introduce change. They’re quite influential organisms ecologically. Earthworms can dramatically change various soil properties. This in turn can impact anything living or growing in that soil.”

MICHAEL MCTAVISH, PhD candidate in Environment and Resource Studies at the University of Waterloo

Waterloo researcher wins prestigious award

McTavish is the recent winner of the prestigious Natural Sciences and Engineering Research Council of Canada (NSERC) André Hamer Postgraduate Prize for the most outstanding candidate in their doctoral scholarship competition.

“Even in a research group with so many excellent and award-winning scholars, Michael's achievement is unprecedented," says Stephen Murphy, McTavish’s supervisor and Chair of Environment and Resource Studies.

Michael McTavish

But why, of all invasive species, would a gifted researcher like McTavish focus on worms? “One of the things about the earthworm invasion is that we don’t have a great way to control it,” McTavish explains. “We can try and stop them from being introduced, but once earthworms are in the soil, they’re rather hard to get rid of.”

Climate change affects how we manage invasive species

As such, worms pose some challenging questions for how we think about ecological conservation and restoration. With a rapidly expanding human footprint, on-going climate change impacts, and ecologically-impactful invaders like earthworms, is fighting to preserve a forest exactly as it was 200 years ago still meaningful or even possible?

McTavish isn’t sure. And that’s exactly what his work is trying to answer. “Restoration can be very traditional, even dogmatic, pushing to get to something that is no longer attainable or desirable,” he says. “I’m asking, when and how should we be pursuing related but new targets?”

This pragmatic argument to accept and integrate some exotic species as opposed to always stopping them could be considered unethical and risky.

Invasive earthworms are difficult to control 

“The moment people start talking about ‘engineering’ ecosystems for a new feature or a function it didn’t do before, people worry that we are trying to wrest too much control from Mother Nature. With some invasions like earthworms, however, there sometimes is no other option than embracing some amount of novelty.”


This challenge raises the other tough question:  What exactly are our natural spaces for?

“How do we argue that this novelty can be pragmatically necessary, and also completely acceptable in some cases?” asks McTavish. “When earthworms get into a forest, it doesn’t fall down or disappear. It looks a little different, but it can still be an ecologically-functioning ecosystem that people love and care about. Ultimately, situations like this require us to think long and hard about why and for what we restore in the first place.”

Photo credit: afhunta/iStock/Thinkstock