Invasion of the killer earthworms

It sounds like a B-grade horror movie.  Millions of earthworms, moving silently beneath soil, wreaking havoc until the entire planet is uninhabitable.  Sound a little far-fetched?  Not to ecologists that study northern hardwood forests.  While most of us grew up thinking earthworms were ubiquitous, turns out they are not native in parts of North America that were covered with ice during the last glacial period.  Most of us also grew up thinking that earthworms where the good guys/girls (they’re hermaphroditic), churning up compacted soil and leaving nutrient-rich castings behind.  In many northern hardwood forests, however, exotic earthworms, have become invasive and ecologists believe they are having profound effect on ecosystems.

I have to admit I hadn’t paid that much attention to the invasive earthworm issue but I attended a seminar last week by Dr. Lee Frelich, Director of the Center for Forest Ecology at the University of Minnesota.  Dr. Frelich’s seminar touched on several areas of research, almost all of it extremely depressing, related to climate change and invasive species.  He and his colleagues have documented significant changes in soil ecosystem processes and plant succession associated with increasing populations of earthworms.  Nightcrawlers, in particular, cause a lot of problems because they consume fresh leaf litter causing it to decompose at a much faster rate compared to un-invaded ecosystems.  The net result of these soil changes is that few trees or shrubs can reproduce in the understory.  Over time this may lead to a very different looking forest than exists there today.

Of course, we may end up with a very different forest in any event, given some of the climate change scenarios Dr. Frelich presented.  One worst-case model predicted the climate of the Boundary Waters area of Minnesota would resemble that of present-day Oklahoma City by the end of the century.  But I try not to worry; I figure by that point I’ll be food for the earthworms anyway.



For more info on the earthworms that ate Minnesota, check out these links, if you dare…

12 thoughts on “Invasion of the killer earthworms”

  1. (Couldn’t stand to see this with no comments so here’s my 2 cents worth.)
    I like earthworms. I’ve seen them in a huge tangled jumbled mass under a compost pile, working away at decomposing kitchen scraps. I’ve used them to catch fish while I sat on the bank of a pond and watched a red and white bobber floating on lazy summer days. I’ve seen a terrapin digging them up under a rabbit hutch and gulping them down like candy. I enjoy having them working in my enriched garden soil. Generally they make me feel good. But now I’m not sure I’ll ever feel the same about them. Alien invaders? Maybe those in my yard (Virginia) are natives, but who knows for sure. I personally think the jury is still out on their benefit/harm in the environment. Could it be that the northern forests of millenia ago were more like what is being seen today instead
    of what was in the recent past? Is there any evidence that there EVER were earthworms present there? Just aksing…

  2. I remember reading an article years ago referencing the UP of Michigan having a massive amount of earthworms. Hopefully that wasn’t a Yooper myth.

  3. Earthworms may be beneficial in some ways, but the jury is definitely NOT out on what earthworms do to northern hardwood forest ecosystems. Once you’ve seen a forest floor almost completely devoid of leaf litter and other organic matter, you will never think about earthworms the same way again.

  4. I read about this problem (maybe in Amy Stewart’s great book about earthworms?); apparently the damage has already been measurable. I guess just like any ecosystem, any changes affect everything, some more quickly than others. I’m not sure what the “fix” for something like this would be.

  5. I have read that earthworms were present in North America before the last ice age; that the ice pushed their range south, and that they are slowly moving back north anyway. I would very much like to know, from the perspective of a scientist, why we should now be worrying that our activities are causing earthworms to be re-established early. Thank you.

  6. Michelle, you’re right. Many of these areas had earthworms before the last glacial period. There are two issues here. Left to their own devices, native earthworms, as you might imagine, migrate very slowly and would likely not have been able to migrate this far yet. Second, and more importantly, there are several species of exotic earthworms, including nightcrawlers, that are much more effective at removing litter than native species. The result has been a host of ecological issues including increased nutrient leaching and altered successional patterns.

  7. Thanks for the clarification, Bert. Do you know if there is there any data available on how long it is expected for native earthworms to return to northern hardwood forests? Thanks.

  8. Sometimes I can’t help but compare the alarmist warnings of scientists to superstitions created in days of old. Not saying there is no merit in concern over the invasive worm species; I read about it a year or so ago and it is sad about the eastern hardwood forests. But if the easterners have to, if their forests are out and out destroyed, maybe they can plant faster growing tree species that will net more usable timber and oxygen.

    But consider this: if the native worms are moving north, they have many barriers. We’ve built structures such as roads (bases of which go too deep for some worms to go under) and dammed rivers, sprayed herbicides and pesticides for miles and miles of farmland, (which kills worms) fed our animals dewormers resulting in literally tons of contaminated animal poop (that also kills worms if they are near the contaminated poop, and remember folks, they eat that stuff) and many other interferences. So we’ll never actually know how far north and at what rate the native worms would have made it because we’ve already skewed the equation.

    And why this alarmist tone when WA state has native earthworms (it was not covered during the last glaciation). Would you prefer us to think that every worm we see is an invasive species?? Again with the alarmist superstitions.

    All that being said, I farm Eudrillus eugeniae and chose that species because it cannot survive in temps below 50 degrees or in soil that has a low pH, which most all unamended soil in the PNW has. With care they can survive in your outdoor compost pile if you take pains with the temp and pH, but they would never survive the wild here. Just a little thought, a little planning goes a long way towards protecting what we have. But as far as I can tell there hasn’t been any documented worm invasions in the PNW yet.

  9. Corinna:
    I think we have some points of agreement and disagreement (or at least corrections of fact). I agree there is an alarmist tendency in discussing invasive species. I was trying to inject a little campy humor with the ‘Invasion of the killer earthworms’ heading. But we often see dire language (devastating impacts, ecological havoc) when the subject of invasives is raised. If you follow the blog, you’ll realize I don’t fall in that camp – in this case I was relaying a research program I found interesting. A couple points of correction. Eastern forests won’t necessarily be destroyed but species composition is changing due to earthworm effects. The Puget lowlands of western were covered with the Cordilleran ice sheet during the last glacial period down to the area south of Olympia. Lastly, at least one study at WSU found that invasive earthworms dominate over natives in the Palouse

    1. I have always liked earthworms and feel they are good for the garden and over all these years they have always looked much the same. In April last year, my borders had the usual satisfactory number of worms. This year, however, so far I haven’t come across a single worm but what I have seen are horrid-looking things, similar length as a worm, thin, orange/white, slightly flattish sometimes and pointed at the end that moves. What are they and where are my worms? Val..

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