Earthworms: The Beauty and the Beast

Posted by: Alison O'Connor, Horticulture Agent in Larimer County

An earthworm; photo by Alamy

Ok, I’ll admit….I’ve never given much thought to earthworms, except when I was growing up in Minnesota and squeamishly threading one on my fishing hook.  I found that sunnies preferred fat, juicy nightcrawlers and they were the easiest fish to take off my hook (aside from perch).  But I digress…

Earthworms.  Everyone knows about them, but are they good or bad?  Do they have a useful purpose?  What’s their role in our landscapes?

First, did you know that what we call “nightcrawlers” are not native to North America?  (I’ll give you a second to pick up your gaping jaw.)  It’s true.  These are introduced arthropods from Europe that joined our early settlers on their boats—soil and rocks were used to help ballast the ships sailing west across the Atlantic Ocean.  When they arrived, they dumped out the soil and rocks (and nightcrawlers) and “traded” with North American goodies to bring back to Europe.  The first example of “Fair Trade.”

These non-natives have out-competed our native populations of earthworms…so much so that it’s difficult to find any native earthworm species throughout the U.S.  In fact, the Minnesota Department of Natural Resources labels them as an invasive species in Minnesota (take note, fisher-people!).  The worms in the northern state are so productive in the forested areas that there is virtually no duff or forest litter left.  What this means for the trees is fewer nutrients and a lot more soil erosion.  Plus, the slimy guys have also changed the ecology of native wildflower populations.  It’s a pretty interesting article, if you care to read it. 

On the plus side, now that the worms are permanent residents in Colorado (and not a part of the 51^st state), they do provide some benefits to our landscapes.  They are great at de-compacting our clay soils, recycling organic matter and freeing up nutrients for plant use.  If you have a “lumpy lawn”, you’ve got worms.  This is not necessarily a bad thing, unless you like to play croquet or have active slip-n-slide users. 

Earthworm in estivation; photo by Jacob McDaniel

A recent study in Colorado found that earthworms can survive drought for up to three weeks!  While water is a necessity for regular earthworm function (it keeps their slime slimy, which helps them glide like butta’ through the soil), if soils begin to dry, earthworms go into estivation, a “summer-like hibernation.”  Personally, I’d enjoy a respite of estivation during hot summer months, myself.  Researcher Jacob McDaniel, a research associate at Colorado State University, found that during estivation, the earthworm curls itself into a tight ball to reduce contact with the soil (thus reducing water loss from its body).  

Various tests were conducted—including constant water (the control) and one, two and three weeks without any added water to the soil.  Though 14% of the worms died in the 3-week drought, the remaining 86% recovered after the soil was rewetted.  Wow.  That’s amazing resiliency, little earthworms!

Earthworms are a major issue on golf courses…the lumpiness they cause makes putting difficult and golfers crabby.  And they are really good at killing grass by popping out of the ground and splaying their castings (poo) and soil on top of the turf surface.  Nightcrawlers can also live for many years and inhabit the same burrows.  Like any good homeowner, they frequently clean house…but instead of keeping their trash out of site, they display it for all to see—on top of the turf surface.  

Earthworm casting on Bethesda golf course;
photo courtesy of Bethesda Country Club

Golf course superintendents do have ways to discourage earthworm activity.  One way is sand topdressing—the sand is irritating to the worm’s body (but we do not recommend you do this on your home lawn).  Another solution is trying to keep the course as dry as possible.  Earthworms will gravitate to areas of higher moisture near streams and water hazards.  There are no pesticides labeled for the control of earthworms.

As a homeowner, you can encourage earthworm populations by reducing tilling in your garden and adding organic matter to your soil.  Recycling your turf clippings will also feed the worms, which is like “cotton candy” to them.  Keeping your lawn and garden moist will make for happy worms.  But if you don’t like them or are finding them destructive, there’s little you can do.  Try rolling the lawn to smooth out the bumps and dry down your garden areas.  But really it’s probably better to accept and welcome them, since they clearly have claimed your landscape for their own and have no plans on leaving.

So the choice is yours regarding our fellow worm—good guy or bad guy?  I was always a fan of Slimy on Sesame Street.  

Slimy! (photo courtesy of Wikipedia)