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Wednesday, 20 June 2007
Earthworm Invaders


Daily Telegram (Superior, WI)

By Emily Kram

May 5--After a heavy rain, it's not uncommon to see swarms of earthworms wriggling on the street and sidewalks. Even when tilling the soil or just digging a hole, you're almost guaranteed to see an earthworm or two.

Would it surprise you, then, to know that Wisconsin and Minnesota have no native terrestrial earthworms? If there ever were native earthworms in the Great Lakes region, they were killed thousands of years ago when glaciers covered the area. All of the earthworms commonly seen today are non-native species, most of which were introduced to the region by European settlers.

Not only are these earthworms exotic, they are also classified as invasive -- meaning they are likely to harm the environment and displace native species.

Certainly you've heard, as I have, that earthworms are beneficial creatures, especially for compost and gardens. Because of this, many fishers just dump their unused bait outside, thinking they are helping the environment. The truth, however, is that earthworms can be very destructive.

The concerns surrounding earthworms have to do with forested regions. While earthworms may help to aerate and fertilize soil in lawns and gardens, they aren't nearly as benevolent in the soil of forests.

When earthworms are not present, dead leaves and organic matter decompose slowly to form a layer called duff. When earthworms are present, they digest the leaves and organic matter on the forest floor, reducing, or sometimes eliminating, the layer of duff.

Wisconsin and Minnesota's ecosystems developed without earthworms, so native plants and animals have come to depend upon duff. With the absence of duff, young saplings and native ferns and wildflowers fade away. In addition, duff helps to prevent soil erosion. When the layer of duff is gone, erosion increases.

So what can you do? As far as eliminating worms already in the soil, not much. You can, however, help prevent earthworms from spreading to forested areas. One of the simplest ways to do this is to dispose of your unused bait in the trash this fishing season. This goes for not only earthworms, but all bait. You can never be too careful when it comes to preventing the spread of invasive species, native or exotic.

When not aided by humans, earthworms take quite some time to spread into new areas. According to the Minnesota DNR website, earthworms move less than half a mile over 100 years. Because they move at such a slow rate, it should take earthworms many years to spread to new forests in the Great Lakes region ... as long as we don't give them a helping hand.

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