This Issue:

Table of Contents

Cover Story

Cover Story - Spanish Version

Mini-Lesson

Comprehension Quiz

Teacher's Guide and Worksheets

Alien Invasion

Spanish Translation

By Kathryn R. Hoffman

This summer, the quiet town of Crofton, Maryland, was invaded by aliens. Townspeople swapped fearful stories of slippery, hungry predators that would eat anything they could fit in their jaws. Soon, the whole country was on the alert. The Bush administration promised to keep out the strange creatures. Said U.S. Interior Secretary Gail Norton: "These are like something from a bad horror movie."

But this is no movie, and the aliens aren’t from outer space. They were brought here by humans! This creepy tale is about a fish called the northern snakehead. It is from Southeast Asia, where it is seen as a harmless swamp fish. But in the U.S., the fish is an invasive, or alien, species. It is part of a growing threat to American ecosystems. Last month, Maryland wildlife officials poisoned the lake where the snakeheads lived before the fish could do serious damage.

They Come by Air and Sea
Over the past 200 years, thousands of foreign plant and animal species have settled in the U.S. Most travel into the country with humans. Some nonnative species, such as a plant called kudzu, were brought here on purpose—for people’s gardens. Others, like the Asian long-horned beetle, slip in accidentally with cargo on boats or planes.

Some of these nonnative species have become invasive. This means that their introduction has caused environmental, economic or health problems in our country. Both kudzu and the Asian long-horned beetle have become problems. Kudzu vines smother trees and bushes. The Asian long-horned beetle turned up in Brooklyn, New York, six years ago and has since traveled to Chicago, Illinois. The wood-chomping beetles have killed thousands of healthy trees.

Many foreign species have no natural enemies in their new environment. This allows them to spread rapidly and threaten the survival of native species. "In eastern Africa, the (invasive) Nile perch has caused the extinction of 300 species of fish," says Guy McPherson, an ecologist at the University of Arizona. Scientists feared that the snakehead, which can flop from pond to pond across small pieces of land, would have a similar effect on U.S. waterways.

No one wants to keep out all foreign species. Many scientists are saying we should be more practical. Instead of trying to wipe out all foreign species, we should figure out which new creatures are desirable and which are undesirable. "Life would be easier if we could say native equals good and exotic is bad, " says Mark Davis, an ecologist at Macalester College in St. Paul, Minnesota. "It’s not that simple."

Davis says that most nonnative species are harmless. Some are even beneficial to the environment. The European honeybee, for example, is important in agriculture. It provides pollination for valuable crops.

"But don’t you wonder what the honeybee replaced?" asks McPherson. He says the European invader may have wiped out a native bee that did the same work. "We don’t know what we’re losing by introducing new species," he says.

A Balancing Act
Plants and animals do have a special place in their original environments. "Native species have a role in the ecosystem that they evolved into," says researcher Faith Campbell. "There’s a balance."

The U.S. and other countries around the world are doing what they can to preserve this balance. Most wildlife officials agree that we may not be able to stop the invasions. But we can work to protect healthy native species from harmful foreign ones. Says Campbell: "We have a responsibility to take care of the environment where we live."

---

America’s Most Unwanted

Researchers say that humans have brought about 50,000 foreign species into the United States. Not all of them are harmful, but a report by Cornell University says that fixing the problems caused by invasive species costs the U.S. more than $138 billion a year. Here is a look at some of our expensive guests.

ZEBRA MUSSEL This invader from Eastern Europe has caused problems in the Great Lakes for years. Now, zebra mussels are threatening waterways in northern Virginia. They upset the food chain in lakes and damage the pipes of power plants and water systems.

NUTRIA This rodent was brought here from South America for the fur trade. By digging and gnawing at grasses, it has ruined 100,000 acres of marshland in Louisiana and 8,000 acres in Maryland.

ASIAN LONG-HORNED BEETLE These pests came to the U.S. from China—where they’re also a problem. Most beetles only munch on dead or dying trees, but these bugs prefer healthy wood!

CARP The Mississippi River is teeming with several kinds of carp from Asia. They compete with native fish for food and threaten the fishing industry. Some leap into boats and hit boaters on the head!

COQUI (ko-kee) This frog is beloved in Puerto Rico but is seen as an annoying pest in Hawaii. The noisy coquis compete with the islands’ rare birds for food and eat insects that pollinate flowers.

Next: Wildfire in the West!