The Worm Turns

EarthwormThis morning when I was doing my regular news search online, I came across two stories that stopped me cold: we’re being invaded. By worms.

Yep. Worms. Not the slimy invertebrates who write scurrilous, defamatory self-aggrandizing blogs and whine about free speech when they are taken to court over their lies, but actual earthworms. Nightcrawlers.

The little invertebrates we have in our gardens and at the end of fishhooks. They’re invading Canada. And they’re doing it rather quickly. For worms, that is. They’re actually being aided and abetted by us. Humans are the reason they’re here, and the main reason they are spreading at something slower than even a snail’s languid pace:

D. octaedra populations currently expand about 16 meters (around 52 feet) per year. At that rate, a single worm and its descendants—they reproduce asexually, so one worm reproduces on its own—could expand to cover the length of an American football field in six to seven years.

They spread thanks to hitching rides with humans, on cars, tires, shoes – and of course in fishing tackle boxes. Worm eggs and cocoons also travel as hitchhikers. Anglers who release their unused earthworms after a day’s fishing have helped the spread even more, so much so that PR campaigns are in full swing to stop anglers releasing them in the woods.

Non-native earthworms have been identified as a major threat to our forests:

…the impact of earthworms on forest vegetation was listed in 2011 as one of the top 15 emerging global conservation issues by the scholarly journal Trends in Ecology and Evolution.

The common everyday garden earthworm isn’t a native to North America. It’s a European invader, brought by settlers. Asian species have also been brought ashore more recently, and may even be destructive in your garden.

I didn’t know any of this until I read about the invasion, this morning on eCanada:

None of the earthworm species found in Canada are native to North America… Earthworms were mostly wiped out during the last ice age some 11,000 years ago and were only reintroduced to North America during European settlement. Canada’s only native species are found in areas that were untouched by glaciers, such as Vancouver Island.

The earthworms’ northern migration is largely the result of human interference and activities such as fishing, boating and camping. Earthworms that don’t end up on a fishing hook often end up discarded in the wilderness or in the water. Worms and worm cocoons also hitchhike their way into the wild, sticking to tire treads or wheel wells before ending up in the forest.

Who knew? I always thought earthworms were good for the soil. Suddenly they are villainous little creatures, seditiously undermining the very soil under our feet. Just like the bloggers.

The Great Lakes Worm Watch site says:

Ask anyone on the street if earthworms are good for ecosystems and you will undoubtedly receive a resounding “YES!”. When asked why, they may say something like “earthworms mix and aerate the soil”. It is a basic ecological concept that we may have learned as early as kindergarten. However, recent research on invasion of these seemingly benevolent creatures into previously earthworm-free hardwood forests of the Great Lakes Region has seriously challenged that belief.

It concludes, “… exotic earthworms may pose a grave threaten the biodiversity and long term stability of hardwood forest ecosystems in the region.” Scary.

Wikipedia adds more:

Invasive species of earthworms, specifically from the suborder Lumbricina, have migrated and spread through North America.[1] Their introduction is having drastic effects on the multiple nutrient cycles in temperate or temperate-coniferous forests. These earthworms increase the cycling and leaching of nutrients by breaking up decaying organic matter and spreading it into the soil. Since these northern forests rely on thick layers of decaying organic matter for growth and nutrition, they are diminishing in diversity and young plants struggle in these environments. Many species of trees and other plants may be incapable of surviving such drastic changes in available nutrients.[2] This change in the plant diversity directly affects the other organisms of the environment and often leads to increased invasions of other exotic species as well as overall temperate forest decline.

The Great Lakes Worm Watch site says earthworms native to this region were wiped out by the glaciers 11,000 year ago:

We have no evidence that earthworms ever inhabited the Great Lakes region before European settlement.  Even if they did, the glaciers killed any native North American earthworms in our region.  For the last 11,000 years since the glaciers receded, Great Lakes forest ecosystems developed without earthworms.
There are over 100 species of native North American earthworms in unglaciated areas of North America such as the southeastern U.S. and the Pacific Northwest.  However, native species have either been too slow to move northwards on their own or they are not able to survive in more harsh northern climates.

What is good for the garden isn’t necessary good for the forest, as TechieNews pointed out:

D. octaedra eats leaves that fall to the forest floor. The worms burrow beneath the surface where they mix different layers of soil and change the soil pH. Ultimately, these changes alter how organic and inorganic matter decomposes and result in fewer small invertebrates in the soil. Other types of worms have even been found to cause native plants living on the forest floor to die and birds that nest there to lose their habitat.
Since the forest hosts no native worms, D. octaedra and other invasive earthworms are able to spread unchecked.

Earthworms have been blamed on the die-out of trilliums and other native plants in North American forests, and even to the loss of songbirds, according to the Star Tribune:

The worms eat leaf litter on the forest floor, so you end up with bare ground… And they compact the soil and cause nutrients, especially phosphorus and nitrates, to leech out of the soil into the water… The growth of the forest is actually stunted… We’ve seen about a 30 percent reduction in sugar maple growth rates… Earthworms hit trillium, violets and orchids really hard…

This could have an impact on the local maple syrup industry, too.

In another, related story, TechieNews announced there will be a mobile app for tracking earthworms in Alberta – assuming Albertans still giddy from the resounding NDP victory in the recent provincial election are so inclined to do so – coming sometime this spring:

In an effort to track and possibly curtail their territory expansion, study co-author Erin Cameron and colleagues at the University of Alberta have developed a “citizen science program” and mobile app dubbed ‘Worm Tracker’, which will be released later this spring.

“The website for our program has sampling instructions and curricular materials for teachers, and participants can also view maps of their data and all other data that is collected,” said Cameron.

There’s no information whether this will be available for similar tracking studies in other provinces. However, the Great Lakes Worm Watch site has information about how to participate in this region.

Seems I have to revise my impression about earthworms. They’re no longer the beneficial creatures I imagined. Well, no more saving them from the driveway after a rain.


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