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Scientists Sound The Alarm About Invasive 'Crazy Worms' Found In Maine

University of Wisconsin via BDN
The Asian crazy worm is on the march in Maine, leaving soil -- and plants -- deprived of valuable nutrients.

If you're a gardener or a composter, you likely regard earthworms as your firm friends: nature's own little rototillers.

But it might surprise you to know that earthworms aren't actually native to Maine at all, and they've even been labeled invasive in some cases. Researchers at the University of Maine recently uncovered a population of European worms that have taken up residence in Aroostook County timberlands, and there are others around the state as well: different populations, different species.

To learn more, All Things Considered Host Jennifer Mitchell spoke with Maine state horticulturist Gary fish.

Note: This interview has been lightly edited for clarity.

Mitchell: So Gary, I'm guessing that a lot of people are unaccustomed to thinking of earthworms as something that might not necessarily belong in an ecosystem because they're so ever present. So do they belong? And where do they belong?

Fish: Well, the earthworms that we have in Maine do not belong here. They all come from either Europe or Asia. Most of the early ones were brought from Europe and came in ship ballast or in plants that they brought with them. Oftentimes, some populations can actually be pegged to where people planted lilacs many, many years ago.

And we don't have native earthworms in Maine because they were all wiped out by the glaciers, and when they receded 11,000 years ago, there were no earthworms here. There were native earthworms much further south, but none of them moved back into Maine. And what we have now are the invasive earthworms that come from other parts of the world.

So if none of the earthworms in Maine are native to here, does that make them all invasive? Because it seems like it's only very relatively recently that I've seen the term 'invasive' applied to earthworms at all. So is there a difference between being non-native and invasive, I suppose?

That depends upon where they are. All worms are not a friend of the forest. They are bad for the forest, whether they are European or Asian. There are European worms like nightcrawlers, or your typical earthworm, as we call them, that can be beneficial for the garden, because they go deep into the ground, and they create pores that help to get water to the roots or get air to the roots. And that's where they're beneficial for our vegetable gardens. Or even in some instances for our lawns or even some of our other plants.

The Asian worms, the crazy worms, the jumping worms, are pretty much foe for everything. We call them Amynthas worms because that's the genus that most of them are in. They cause problems in turf, they can kill turf. They can kill perennial plants. And they are a huge problem in the forest. They eat the forest duff much faster than a lot of the other European worms because they stay right in that duff, they don't go deep into the ground. They stay right at that duff level, and just eat it all up really fast.

And it makes it for a horrible planting site, or growing site for all the nice plants that grow in the forest. And also, eventually, it ruins the soil for the trees.

A lot of folks are gardening right about now, and obviously fishing. Some people are new to those pursuits, having taken them up this past year. So as people are going about buying plants, ordering things online, doing the things that they do that might bring them into contact with worms, what should they be keeping in mind?

Basically, we're trying to get people to not move them around, and especially not into the forest. Anglers that might drop worms by the wayside as they throw them out, they should never do that; they should always bring back what they carry in -- you know, carry in, carry out.

And if you are moving around soil or mulch, or any other kind of compost, they can be infested with these worms, especially with the cocoons that you can't see, and easily start a new population because they're what we call parthenogenic. It only takes one worm to start a population. They don't have to have sex to have babies.

Ultimately, then, what is at stake here?

They can have a severe impact on, let's say, the maple syrup trade. They tend to really impact maple trees. All trees are fairly shallow rooted, but maple trees tend to be even more shallow rooted. And without that protective leaf litter and duff layer, they become very stressed, and they're more susceptible to insects and diseases, and they're less likely to grow very fast. So it impacts not only the lumber industry but also other industries that rely on a healthy forest, or even our recreation industry.

The other issue with these worms is that they really impact wildlife, especially that which lives at the forest floor and depends upon the leaf litter that's there: birds like the veery or the ovenbird or the woodcock, they all nest in that duff layer and without that there, they don't have a place to nest. Salamanders, as well, are greatly impacted by these worms and have really no place to go if that duff layer is not there.

And I think that spring ephemerals, many of the plants that we love to see when we go hiking, like mayapple or bloodroot, or trilliums, trout lily, those are all severely impacted by these worms. They have no place to grow and live, without that forest litter.

Corrected: June 9, 2021 at 12:39 PM EDT
Because of a transcription error, a previous version of this piece misidentified the Amynthas genus of worms as "Memphis."