Earthworms Threaten US Forests. Is Composting Really to Blame?

earthworms forest soil photo

Image credit: Yun Huang Yong, used under Creative Commons license.

As someone who has posted this fabulous infographic on which composting method is best for you, and videos of DIY compost tumblers and build your own worm bins, I would hope that my commitment to composting is beyond question.

But having just written about the disturbing news that poorly managed compost can kill dogs, I'm afraid I have another cautionary take to share—apparently earthworms can kill forests. And composting may be partially to blame. Then again, it may not...Lloyd wrote about invasive earthworms putting forests in danger before, explaining that because earthworms are so fast at munching through leaf litter (a trait that makes them very attractive to compost fanatics), they can make forest soils less stable—meaning nutrients are washed away by rain before they can be bound up in the soil. While Lloyd's post identified fishermen and bait shops as a primary culprit in spreading the little wrigglers around, UPI reports that Colgate University researchers have shown that composting and other human activities play a role in spreading worms into forests too:

Researchers from Colgate University in New York, in a study published in the journal Human Ecology, say humans spread earthworms -- both inadvertently via horticulture and land disturbance, but also knowingly through composting and careless disposal of fish bait. Human introduction of exotic earthworm species can be traced as far back as European settlers arriving in North America and dumping ship ballast, a mixture of soil and gravel, onto the land, the researchers said.

As an avid composter who lives in the woods, I was hoping the article would include some specific tips on how to avoid spreading worms around. I am certainly not making plans for worm composting outside in my garden anytime soon, but I have seen an increase in worms since I started actively gardening—and can only assume that they will spread into the woods around me.

Looking for a little more information, I found this article from Sustainable Gardening on the mysteries of invasive worms, which argues that most research suggests that nightcrawlers (a common bait worm unsuitable for composting) are the real problem, while red wigglers (the most common composting worm) will not survive outside the composting environment in many areas of the US. Nevertheless, it notes, some experts recommend freezing worm casting before adding them to your garden—and certainly be careful to buy appropriate composting worms from companies that know what they are selling.

If anyone has further resources on whether or not composting with worms can endanger forests, please share in the comments below.

More on Composting
Which Composting Method is Right For You? Infographic Explains All
How to Build a DIY Compost Tumbler
Build Your Own Worm Bin (Video)

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