Cindy Hale, an ecologist at the University of Minnesota, answers e-mails from a lot of distraught citizens of the Great Lakes region. The residents, it seems, have introduced certain earthworms into their gardens, she says, “and now they’ve got that ‘nothing grows here syndrome.’”
Long considered a gardener’s friend, earthworms can loosen and aerate the soil. But the story is different in the Great Lakes region. The last Ice Age wiped out native earthworms 10,000 years ago, and ever since the Northeast forest has evolved without the crawlers, Hale says. But now earthworms are back, a product of fishers who toss their worms into the forest, of off-road vehicles and lumber trucks that carry them in the treads of their tires, and of people who bring in mulch—and any worms that might be in it—from other areas.
As invasive creatures, the earthworms wreak the most havoc with hardwood forests, such as those consisting of maple, basswood, red oak, poplar or birch species. (Conifer-dominated forests seem to experience less dramatic impacts.) According to Peter Groffman, a microbial ecologist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., northern hardwood forests have relied on thick layers of leaf litter that serve as a rooting medium. The earthworms, Groffman reports, “come into an area with a thick organic mat, and two to five years later that layer is gone.”
As a result, some northern hardwood forests that once had a lush understory now have but a single species of native herb and virtually no tree seedlings. Evidently, earthworms change the forest soils from a fungal to a bacterial-dominated system, which speeds up the conversion of leaf detritus to mineral compounds and thereby potentially robs plants of organic nutrients.
Not all foreign earthworms are destructive. Of the 5,000 species around the globe, only about 16 of the European and Asian varieties do the real damage. One of them is the night crawler (Lumbricus terrestris), a popular fish bait that can measure up to 15 to 20 centimeters (six to eight inches). Another is the Alabama jumper (Amynthas agrestis)—also known as the snake worm or crazy worm—an aggressive Asian worm that lives at high densities and can literally jump off the ground or out of a bait can, according to fishing lore. A voracious eater, it does the most harm to the soil.
The presence of the earthworms affects more than just the plants. John Maerz, a wildlife ecologist at the University of Georgia, says that adult salamanders that consume these earthworms are more successful at reproduction but that earthworms are too big for juvenile salamanders to eat, which leads to a net loss in salamander numbers. The amphibians themselves, Maerz notes, are an important prey species for “snakes, small mammals, turkeys and a host of forest creatures.”
Once established, earthworms are impossible to remove from the environment, Hale says. Concerned about their impact, the U.S. Department of Agriculture recently awarded Hale and her fellow biologists a three-year, $397,500 grant to study the ecology of the earthworm invasions in cold-temperate hardwood forests. The scientists also hope to answer questions about nutrient and carbon cycling—including whether the earthworm activity helps to sequester carbon in the soil or releases it back into the atmosphere. “The jury is still out on this issue,” Hale explains.
Researchers agree that the best hope is to contain the worms, which spread only five to 10 meters a year on their own. That may mean new regulations governing off-road vehicles, bait disposal by anglers, or equipment hygiene and use in the logging industry. Hale would like to control community mulch piles as well: “I remember when I first heard about them, I thought, what a great idea, but think about it. You take leaves, weed seeds and earthworms from all over, bring them in, mix them up and then disperse them back out. That’s a horrible idea.”
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12 Comments
Add CommentO'my god earth worms are causing Global Warming. We need a few more million dollars to study the problem and form a plan to save the planet from total distruction. May we should line up a few virgins to sacrifice to the gods to save us. Or maybe not and just tell the good dr. to study something of greater importance. Sometimes you can't do anything about change just deal with it.
Reply | Report Abuse | Link to thisWhen the first response is sarcasm, it must mean you really have nothing to contribute. Way to troll for any mention of AGW and miss the actual point of the article.
Reply | Report Abuse | Link to thisI really want to chime in and agree with he second response. Attacking serious issues just because you are too dim to understand them or because they conflict with your political agenda is the kind of childish behavior that has led us straight into the mess we are in.
Reply | Report Abuse | Link to thisThis story is an important story. It points out, among other things, that managing ecosystems is a much more complicated problem than most people imagine -- almost all green-minded people would agree that community mulching and composting services are a good idea, but here we see the dark side.
So "fishers" pay out money for bait, then throw it away, not where I come from. how would European or Asian worms get there?
Reply | Report Abuse | Link to thisIgnoring the first useless comment ... if this research is accurate, it illustrates yet again that there are consequences in anything we do. We have to start thinking, if we want to leave a habitable planet to our kids, never mind have one ourselves.
Reply | Report Abuse | Link to thisInvasive earthworms come into Canada first via importation in soil under plants from Japan. Canadains, seeing that these worms work very well for fishing, will pack them with Canadian earthworms and sell the lot for fishing bait. That is how they become introduced to our soils. Once introduced to fishing holes along creeks, or discarded in the forests, they will propagate very quickly creating a threat to our wildlife
Reply | Report Abuse | Link to thisWhen worms process material, they leave behind castings. Castings are known for being loaded with beneficial bacteria, and are known for making your plants THRIVE. Why would this area show no growth.
Reply | Report Abuse | Link to thisThere are hundreds of publications from experts (Ohio State, University of North Carolina) that review the benefits of worm castings.
This article is a sham.
When worms process organic material, they leave behind castings. Castings are known for being loaded with beneficial bacteria, and are known for making your plants THRIVE. Why would this area show no growth.
Reply | Report Abuse | Link to thisThere are hundreds of publications from experts (Ohio State, University of North Carolina) that review the benefits of worm castings.
This article is a sham.
When worms process organic material, they leave behind castings. Castings are known for being loaded with beneficial bacteria, and are known for making your plants THRIVE. Why would this area show no growth.
Reply | Report Abuse | Link to thisThere are hundreds of publications from experts (Ohio State, University of North Carolina) that review the benefits of worm castings.
This article is a sham.
No offense, Worm Dude, but your knowledge of invasive earthworms is a sham.
Reply | Report Abuse | Link to thisWorm castings can't stabilize a forest floor microclimate and retain moisture the way a robust leaf-litter bed can. Leaf litter beds provide habitat for wildlife and insulation for the root systems of perennial plants during the winter months. All the nutrients in the world won't help a plant that's drying out faster in the summer and getting colder during the winter. I also doubt that organisms like arthropods and amphibians will find piles of earthworm castings to be preferable habitat to leaf litter beds.
Despite your assertion that all earthworm castings are "loaded with beneficial bacteria", Amynthas agrestis have been shown to digest soil microbes as they move through the topsoil, leaving the soil with fewer net microbes. I haven't seen anything published yet showing exactly how much of an impact that has on plant life, but it certainly doesn't help.
Even if Amynthas castings were plant super-food and teeming with microbes, that still wouldn't substitute for the moisture retaining and insulating properties of a healthy bed of leaf litter. So it's completely logical that these types of leaf-litter eating worms would lead to a net loss in plant diversity, not to mention the negative effects on forest food webs the article also mentioned.
This article highlights that even the most seemingly insignificant thing - such as an invasive earthworm - can have a big impact on our native ecosystems.
"Amynthas agrestis have been shown to digest soil microbes as they move through the topsoil, leaving the soil with fewer net microbes."
Reply | Report Abuse | Link to thisAny proof of this statement?
Here is a link to the paper I referenced, published last year by the Ecological Society of America. Microbe densities were determined through phospholipid fatty acid analysis.
Reply | Report Abuse | Link to thishttp://www.esajournals.org/doi/pdf/10.1890/09-0979.1