Alien invasion.(invasive species)

Before You Read

Ask students: Do you know what the term invasive species means? Why do some insects and animals from outside the United States become a threat when they arrive in this country? What are some ways those species end up in the United States? Invasive species can also be plants; do you know of any nonnative plants in your community?

Vocabulary

ecosystem--a group of plants, animals, and other living organisms that live together in the same area

native species--a plant or an animal that naturally lives in an area or region

Background

* North America has 20 percent more plant species than it did before European colonization, biologists say.

* Ninety percent of immigrant species do no obvious harm to their new home environment.

* The Nature Conservancy estimates that 4,000 species of nonnative plants and 2,300 species of nonnative animals now live in the United States.

* Invasive species include everything from kudzu vines from Asia that is common in the South, to the West Nile virus, which comes from Africa. West Nile virus has been …