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Those Naughty Non-Native Earthworms

Posted by on September 5, 2006 in Worms

8_minn_forest_floor Great stuff from Boostrap Analysis on the publication of some new data from the Minnesota research team I interviewed for The Earth Moved.  I devoted  a chapter to the time I spent there walking through the forest and talking with researchers Cindy Hale and Lee Frelich about their work.  It is true that non-native earthworms have moved into the forest thanks to our behaviour–using worms as fishing bait, laying acres of sod for golf courses near forests, and hitching a ride in fill dirt when a ranger station is being built, living in the roots of potted plants brought in for habitat restoration, etc.   It would have taken non-native worms a couple million years to move across North America at their own rate of speed, but we gave them a lift and finished the job in a couple hundred years instead.

A few things to remember about this research and about our little wormy friends in general:

First, the trouble that non-native worms are causing in the Minnesota forests have a great deal to do with the fact that those forests evolved without earthworms at all.  The northernmost parts of the U.S. were covered by glaciers during the last Ice Age, and native earthworm populations never did form in those areas.  So now non-native worms move in and do what (many species of) earthworms do:  they digest decaying organic matter and transform it into the lovely rich black castings you see here.  (This is a picture I took of the forest floor in Minnesota.) Great news in the vegetable garden, not so great in a forest that depends upon this thick spongy duff layer for seed germination, habitats, etc.

Second, Cindy Hale specifically asked me not to describe the worms as "destroying" the forest.  They are changing the forest, she said. This is not a black-and-white story–"where you once thought worms were great, now we know they are evil."  Instead, the lesson we should take away from this is that every ecosystem is unique, and must be viewed on its own terms.  A few particular species of non-native earthworms may have changed what can grow in this forest, but that doesn’t mean that all species of worms (and there are thousands) are harmful in all situations.  It does mean that when we are thinking about fragile ecological systems, we should remember to take a look underground, something Hale said that her collegues had not been doing.  Consider what’s in your soil when you’re doing habitat restoration.  Remember that even the smallest little spineless creature has power.

And finally, non-native earthworms are, for better or worse, in almost every American backyard.  If you live next to a wilderness area, I’d suggest that you think carefully before introducing anything non-native into your yard, plants included.  But if you live in an ordinary suburban or city neighborhood like I do, your garden already benefits from the glorious work of earthworms and other soil-dwelling organisms.  I’m not about to kick them out of my garden–even if I could.

Bottom line?  There’s nuance in this story, as in most things.  You can learn more about the Minnesota research here.



  1. Oh, yah. There are earthworms and there are earthworms. And then there are Oregon Giant Earthworms that are native forest dwellers — if they still exist and haven’t gone extinct from habitat loss. These things ARE giants, many feet long, and supposedly smell like flowers.

  2. A nice balanced approach. How refreshing!

  3. WOW…thanks for the info! I had no idea this was a problem…..I will forward this link to our local (NE Wisconsin) garden club as a topic for presentation at next winter’s big seminar!

  4. Amazing post, amazing images, I loved it, as I have just completed a draft for my blog about our very own Karmai here in Victoria Australia. Set to be posted this Friday, every Friday I provide my blogfriends with a history post.

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  7. hey !!
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