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written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

I started as a WSU Extension educator on the first day of April in 1980. One of the first calls I received was from a gardener wanting to kill the earthworms in his lawn. Where I came from in New York state earthworms were considered valuable creatures. I wondered if the call was an ‘April Fools’ joke because I hadn’t yet encountered the mounds of soil that nightcrawlers caused in local lawns, making walking across them difficult.

Many have revered earthworms for their recycling of organic matter and building a better soil. Ancient Egyptians declared earthworms to be sacred because of their contributions to agricultural production. While forbidding Egyptian farmers from touching the ‘sacred’ worms might seem silly, USDA research supports that earthworms were critical to the soil fertility of the Nile Valley of ancient Egypt.

Well known natural historian and the father of the theory of evolution, Charles Darwin is not widely known for his earthworm studies. Darwin recognized the value of the earthworm saying, “Without the work of this humble creature, who knows nothing of the benefits he confers upon mankind, agriculture, as we know it, would be very difficult, if not wholly impossible.” His book, ‘The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habits,’ published in 1881, was a better seller than his previous book on the origin of the species.

While respected and valued for their soil building efforts, there is now concern that the many of the earthworms that are recycling organic matter in our agricultural fields, gardens, and compost piles are actually non-native species. In fact, research indicates that the worms creating bumps in lawns, being pulled from the ground by birds, and surfacing on sidewalks during wet weather are predominantly non-native species. WSU and University of Idaho researchers checking out earthworm populations in the Palouse area have found that non-native species of earthworms predominate in both home gardens and agricultural lands.

Why the concern? Scientists are worried about non-native earthworms because they’re so ‘good’ at recycling organic matter, maybe a little too good. In the Great Lakes area of the northeast, these over-achieving non-native worms have invaded hardwood forests that don’t depend on earthworms to recycle organic matter on the forest floor.

The invading worms are removing organic matter that would have decomposed more slowly, releasing nutrients and contributing to the growth of native species. The activities of the non-native earthworms have significantly changed the ecosystem and led to an increase in invasive plant species and a decrease in the diversity of wildlife. Studies indicate that the Lumbricus species, including the robust night crawler, are the most destructive.

Some scientists conjecture that earthworms are contributing to global climate change. Yes, really. Current research is studying whether the worms help sequester carbon in the soil with their recycling activities or if they’re actually releasing it into the atmosphere.

Locally, it’s the bumps in the lawn that are a problem. Unfortunately, there are no chemicals recommended for their control. If you have a nightcrawler problem, you can use a dethatching power rake in early spring to break up the mounds by setting the teeth so that they only go deep enough to break up the mounds without tearing up the grass. Because the worms don’t like dry soil, irrigating less frequently and allowing the top couple of inches to dry out may help discourage their mounding activities. I’ve learned that nightcrawlers in the lawn are no joke.
Published: 4/13/2012 9:49 AM



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