Earthworm Invaders

Podcast

Earthworm Invaders

Transcript

Invasion of the earthworms. I'm Bob Hirshon and this is Science Update.

Northern forests are being invaded by earthworms. This may sound like a good thing, but according to Cynthia Hale, of the University of Minnesota, earthworms can be bad for forests, breaking down organic matter faster than trees can use it. She says the invading worms are a particularly voracious European species, brought over by early American colonists. Native earthworms in the Northern states were wiped out by glaciers during the last ice age.

Hale:
To the untrained eye, most people probably wouldn't notice that there is a big difference, but they're ecologically very different worms. The European species are much more tolerant of wide variations in climate and conditions, and so those are the ones that got brought over by European settlement.

The worms have a big appetite, and quickly devour the dead leaves and plants on the forest floor.

Hale:
That vegetation forms a very thick, spongy mat of slowly decomposing organic material that is anywhere from two to five inches thick.

By quickly chomping through this mat, the worms starve out the plants and animals living there, and could eventually kill the trees themselves. For the American Association For the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

The earth's ecosystems are being invaded! Not by extraterrestrials, but by plants and animals from other parts of the world. These invading species are called non-native or invasive species. They find their way into unsuspecting ecosystems- not by way of a space craft - but instead on the hulls of ocean liners, on the coat tails of unsuspecting travelers, in the soil of imported plants, by wind, water, and air! Although these invasive species can range from minute insects to exquisite plants to immense animals, they all share some common characteristics. Most invasive species reproduce quickly and easily; they are tolerant of a wide range of environmental conditions; and they out-compete native species for sun, water, and nutrients. Invasive species cause damage to natural ecosystems by disrupting the food chain; introducing foreign disease; and interfering with the natural progression and evolution of the system. The invading worms of Northern Minnesota are only one example of how a non-native species can wreak havoc on unsuspecting ecosystems. Use this Science Update to generate a discussion about all types of invasive species and their effects on the native habitats they invade.

As you read or listen to the transcript for this Science Update, and explore the websites below, keep in mind the following questions:

1. How were the "invading worms" brought to the United States?
2. What happened to the native worms that once lived in the United States?
   
3. How do these invading worms differ from the wiped out native worms that once lived in these forests?
4. What do you think the difference is between "native species" and "non-native" or "invading species"?
5. Can you name other species that now live in your area but are not native to it?
6. What are some ways in which non-native species can be introduced into an ecosystem?

Going Further

Have younger students go to The Adventures of Herman from the Urban Programs Resource Network and Worm World from Discovery Communications to learn about how worms where brought to the United States and other fun worm facts in an easy to understand and colorful environment.

A good source of information on non-native species for older students is the United States Geological Survey's Nonindigenous Aquatic Species. This site gives up-to-date information on non-native species all over the US, including their effects to native ecosystems and efforts being used to control them.