All Minnesota worms are invasive, but which ones do you need to worry about? An expert weighs in

MINNEAPOLIS – Last week, the National Weather Service issued a "worm warning" in southern Minnesota. 

The warning was in jest – simply a heads up that residents may see more worms than normal due to heavy rain. But it piqued WCCO's interest in the state's wiggliest inhabitants. So we went to an expert to get the dirt on worms.

READ MORE: NWS Twin Cities issues "worm warning"

Ryan Hueffmeier is the director of the University of Minnesota's Boulder Lake Environmental Learning Center, and he's been studying worms for almost two decades with the Great Lakes Worm Watch program.

What is the Great Lakes Worm Watch program?

HUEFFMEIER: The Great Lakes Worm Watch project is a project that started about 20+ years ago now and it was looking at earthworms that are invasive to Minnesota, and that happens to be every single earthworm you've seen in Minnesota. And it started tracking and trying to figure out what species were here and where and it's still going on, it's a great school project, it's a great community project, it's a great thing to get people involved in and just to learn some basics about soil and science.

What does it mean to say earthworms are "invasive"?

HUEFFMEIER:  Eighteen-thousand-plus years ago the glaciers receded, but they were here, right? They were a mile-plus, two miles thick sheets of ice and as that ice came down from the north it just scoured everything in front of it. So it took everything down to bedrock. So even if there were earthworms here prior to the glaciers, and I have never seen a fossilized earthworm, and that doesn't mean that there couldn't be some, but they're soft-bodied, so maybe they don't necessarily fossilize well, but even if they were here prior, the glaciers and then the permafrost would've killed them. 

And so as the glaciers melted and our forest reset through succession and then we had this grow up of plants, well, I should say mosses and then lichens and then plants. and as it came up the forest we know today, earthworms weren't a part of that mix. It was fungus and bacteria that broke down all the organic matter and that's what, that's how our forest grew. So earthworms were not part of the picture.

How did earthworms get to Minnesota?

HUEFFMEIER: So research thinks that just like all invasive species, us humans are really, really good at moving them. As Europeans were coming over to North America, ballast at the time used to be dirt. So you think of dirt getting shoveled in and then unloaded over here, you could have potential for earthworms. Buckthorn, lilacs, a lot of plants were brought from Europe, in the root balls you would have earthworm cocoons or the eggs that are very tolerant to drought and cold. 

And then there's stories of some farmers and that bringing things intentionally with them, right? Saying, "Whoa, this can't be good for growing anything, there are no earthworms in this soil," and intentionally bringing them. So there's multiple ways they've gotten here but just humans are really good at moving things.

Are there any earthworm species we should be particularly concerned about?

HUEFFMEIER: There is a new species that people are aware of now coming in and that is the jumping worm, the amynthas species, and that is really causing some problems in the southeast and moving its way up into the metro area. This is different than the European earthworms, this is having more of a negative impact on our created ecosystems or our gardens, which most of the earthworms that we know do have some benefits when it comes to our native gardens.

There's 16-plus European earthworm species and they've been here 200, 300 years and there's really not a spot in Minnesota that you're not gonna find a European earthworm. They're pretty established. But these jumping worms are new to the area, they aren't fully well-established, they're just in the southeast and southwest, and so as we talk about it, these European earthworms and the native forest ecosystem, right, they really eat that duff layer, that organic layer and they bring it down to mineral soil. And people are like, "Well, great, they're consuming all this organic matter and turning it into these nutrient packets that plants can take," except our wildflowers and that weren't developed to have this nutrient-rich soil. So that's happening in the forest and then in the garden ecosystems or our created ecosystems, earthworms do, they aerate, these European earthworms, they're aerating the soil, they're creating these nutrients, but these gardens are energy intensive, they're nutrient intensive, so they kinda use up that, so there is kind of a positive in that area. Well, in comes these jumping worms, or in comes these amynthas worms, and they just live in the top couple inches of the soil.  And they can live in really, relay high densities. They're really, really hungry. They eat a lot of organic matter. So what they do is they end up taking that top 2, 3, 4 inches of soil and just turning it into basically like coffee ground soil.

I've seen gardens that people have spent a lot of time and a lot of money to curate and to grow and to see over a couple seasons these jumping worms come through and pretty much disseminate what they've had, where plants are falling over or you can just grab them and just pull them right out of the ground, and there's hundreds of worms just in the root ball. And so they're really, they just take that top soil, that top organic matter and just consume it and turn it into a mineral soil. And now if you don't have any of these fine roots in the soil, you don't have much growing except this soil, this fine, granule soil on top, and you get heavy rains, now what's happening? All that soil is moving out of that system and it's flowing downhill, right? So there's this net loss of nutrients, per se. And so these jumping worms are having a really noticeable impact in, again, our created ecosystems, our home gardens and landscaped lawns, and that has really gotten the attention of people in southeast Minnesota and the Twin Cities area. And that's the one definitely, that's the one to look for. 

If you're going and buying potted plants, if you're going and buying mulch or having soil delivered, you should be asking those businesses if they know about jumping worms. And in my opinion if they don't know about jumping worms or don't have any protocols for assessing them, I wouldn't buy my stuff from them because once they're there – the other part about them is they don't need another worm to mate. They can just do it themselves. And so it just takes one to start a population, and it might take a while for that population to establish, but it really just takes one. So due diligence is really important when it comes to that species.

How do you identify jumping worms?

HUEFFMEIER: These amynthas, and there's about five, I think there's around five species of amynthas that we have, or jumping worms that we have in Minnesota, and they all have a clitellum, or that lump that denotes they're adults on them. And if you can think back to your middle school or high school biology class when you dissected the worms, worms are made of segments, right, they have these distinct segments, and you can actually count them. And jumping worms, if you start at the tip of the nose or mouth and you work back, it's typically 14 or 15 segments and that's when the adult ring starts. On average, European earthworms are 27 to 33 rings back, so they're distinctly further back. 

READ MORE: Some retired couples move to Florida; the Larsons decided to farm worms

And then when you look at that adult ring, in European earthworms, it's puffy. It's big, it's puffy, we say it's like a saddle, it's like a saddle shape, right, it flares out. And in jumping worms it's really smooth and it's really right to the body. 

Another thing is their motion. Jumping worms, I think they move like a snake. They slither, they're strong, they move very un-wormlike. They don't move like the traditional earthworms that we remember growing up with. 

They can also drop their tail. Their tail will fall off and keep wiggling as they move away, that's a defense mechanism. They're called jumping worms because they are really strong and they'll thrash around, and again it's that un-wormlike movement. Because if you come to an area where there's a lot of them and you disturb that soil, they will all start thrashing around and it's a pretty neat thing for your eyes to visually take in. It's something pretty unique to see.

What do you do if you find jumping worms?

HUEFFMEIER: Number one, don't panic. Number two, do not remove everything on your property and bring it somewhere else. You need to just find an area and move them there. Research is pointing that they really like mulch. Put a pile of mulch out and let them come to that area until we can figure something out. Researchers are still working on ways, how to get rid of them and what are effective ways. Sure, you can do it in small patches, but how do you do it in larger patches without basically killing everything else and sterilizing the soil? As you find them, pull them, collect them and kill them. Put them in a plastic bag, throw them in the garbage. But just make sure that you're just not moving things off of site. 

So again the main thing is just due diligence, pay attention to what you're bringing in, know where your plants are coming from. If you can track that plant from when you got it to when it was a seed and where it was, that's great. And then, again, big thing is if these businesses – and a lot of them, a great majority of them do now, but if they don't have any idea bout jumping worms, one, you should tell them to do some research, and if they are, what is their plan? What are they doing with their plants, what are they doing with their mulch to lower the chance of them getting in and spreading? 

How are jumping worms moving through the state?

HUEFFMEIER: So you think about this: whether it's a mulch pile or a compost pile or particularly like a community compost pile, and say you have jumping worms and you're raking up your yard and you pile it all up and you bring it to that community compost pile and now five other people come the next spring and dig in, the potential for spread is there. And a lot of these larger facilities, right, are aware of the problem and they are doing  things, but again, it's something, as a consumer, do your due diligence and ask them what are their precautions they're taking to contain or stop the spread of these jumping worms in those areas.

Why do earthworms come out of the ground when it rains?

HUEFFMEIER: Earthworms do breathe through their skin, right, so they need oxygen in the water. And a lot of times it may be because of their burrows being flooded. But another reason that worms come up when it rains is that's the best time to mate, right? So unlike jumping worms, a lot of these others, they might be both sexes, but they need to share with the other worm, so that's the best time right, because otherwise they're in the soil and they're on multiple levels, they're moving all around the best time is to come, and they dry out pretty quickly so when it's overcast, when it's raining, when it's wet, that's a good time for them to be on the surface. And a lot of times that's what you'll find, you'll find, like nightcrawlers if you ever see them where they're connected or they're two, that's what they're doing, they're mating.

Also movement, a time to move across the landscape is when it's wet. They're able to get to different places. And what those cues are and what they're – we think they're chemical, but we don't know exactly what is happening. It seems to be, again, movement is a time when it's raining and when it's wet. So I think there's lots of different reasons why they come up. But ultimately it's because it is wet, it's wet, the sun isn't out, it's not gonna fry them up and they're able to do things on the surface that they couldn't do most of the other times.

How do worms survive the cold Minnesota winters?

HUEFFMEIER: So it depends the species. There's multiple different techniques. Some just lay cocoons of their eggs. Jumping worms are like that. Their eggs are very tolerant to cold, very tolerant to drought. They're pretty tough. So their eggs, their cocoons will [survive] over winter. And then in the spring they hatch and the process starts. But why do we see adults right away in the spring? Well there are other species, like the nightcrawler go can 4, 5, 6 feet down, and so a lot of them will try to get below the frostline. And if they can succeed, like this year we got a real blanket of snow, and the frostline never got that deep, so a lot of these adult worms can survive into the spring and then we get this wet weather and they're ready to start going they're ready to mate, they're ready to move on.