Earthworm

Do Earthworms pull leaves
into their burrow?

And Are Earthworms Ever Harmful
to the Environment?

There once was an earthworm
So moist & icky
So wrinkled & gooey
Slimy & sticky.
He slid through a garden,
Encircled a rock,
Encountered another
Of night-crawling stock.
He was not very bright,
Could not comprehend
That the worm that he met
Was his other end!

-Anna Best, 1999

The query "do earthworms pull leaves into their burrow?" seems absurd at first blush, but in fact worms do pull decaying leafmatter partway down their tunnel in order to avoid being out where salamanders might get them at night or birds get them during the day if they were eating above ground, or where sun or drying winds might dessicate them.

Small earthworms wouldn't pull anything into their tunnel large enough for us to notice, but a big nightcrawler does, & periodically a set of leaves will be spotted standing straight up on the surface of the ground, with just the stem in the ground. In some locations the worms do such a good job of pulling small leaves underground that all the fallen leaves vanish after one night of rain; it's part of how worms churn the soil & keep organic matter well-stirred into the topsoil.

We tend to think of the doings of worms as one-hundred percent good. But the worm's leaf-snatching activity is not invariably a good thing. Most of the worms in our landscapes are invasive species that did not exist in North America before the arrival of Europeans, & native plants don't always cohabit with these worms successfully. In many forested areas none of these worms are found, if fishermen never introduced them, & in such truly "natural" North American wildernesses the undergrowth can be very different than what is found growing where European worms have gotten established.

There are a large number of native plants that evolved to thrive in decaying leafmatter as it accumulates on the surface of the ground, such as trilliums. Some of the worms burrow very deeply, & pull leaves & beneficial fungus lower than small plants' roots will ever reach. Furthermore, by eating up all the beneficial fungus in a given area, even shrubs & trees can begin to languish, because trees & shrubs cannot process their nutrients without beneficial fungus in the soil to assist in sugar conversion.

Plus the beneficial fungus tare pathogen-retardants. When worms turn the fungus worm-castings or pull it too deep into the soil for plants to access, the entire ecosystem of that area becomes more susceptible to disease.

A layer of leaflitter in a forest serves as the forest's "skin," & without it invasive plant species that did not evolve for leaflittered forest floors get established & crowd out native plants. For all these reasons which begin with the introduction of alien worms, the most sensitive native plant species are dying out of some regions because of the rising population of invasive worms.

In the garden this does not necessarily apply as many of our plants come from the same regions where the worms originate & are adapted to them, & we tend to ammend soils in our gardens with manure topcoatings or other organic methods that keep the microorgism population, including beneficial fungus, very high. Even our habit of watering regularly keeps micropopulations at maximum. And folks such as myself who grow dogtooth lilies & trilliums & native ferns which evolved in heavy leaflitter uneaten by worms, we can make the extra effort to insure that autumn leaves are moved to places around these plants.

But in the nearby woods the worms can be harmful. Forest ecology tends to be stable, or changes from type of forest to another over a period of centuries, unlike a dynamic garden that changes rapidly. The doings of worms in the garden fascilitates rapid growth & rapid changes, but in the wilderness the same worms hamper stability & slow change.

    References (similar articles on-line):

  1. Burton, Dennis, Director of Land Restoration, Schuylkill Center for Environmental Education: The Trouble With Worms
  2. Holdsworth, Andy, Cindy Hale, & Lee Frelich, University of Minnesota Center for Hardwood Ecolony, reviewed by the Minnesota Interangcy Exotic Earthworm Team: Control Those Crawlers.
  3. Hendrix, Paul F., Institute of Ecology & Department of Crop & Soil Sciences, University of Georgia: Biological Invasions Belowground -- Earthworms as Invasive Species.
  4. Dunne, Niall, associate editor of Plants & Garden News: Invasive Earthworms: A Threat to North American Forests.

   



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