Unwelcome Invaders Moving In and Taking Over.

• Position: Brief Article

There's a silent, insidious environmental invasion of the United States that claims billions in damages each year. And we're not talking about something Out of Invasion of the Body Snatchers or Creature from the Black Lagoon.

It's invasive species--plants, animals, insects and microbial pests that have been introduced to the United States from elsewhere via produce shipments, ships, trucks and other ways that can be found to "hitch a ride."

These "foreigners" have had adverse effects, such as reducing profitability of grazing land or choking out native flora and fauna. According to a recent study by researchers at Cornell University, invasive weeds and other species cause an annual $136 billion in economic damage every year.

Every state plays host to hundreds of non-native species. A 1994 state-by-state comparison by the University of California at Davis noted that 7.9 percent of the total flora of the state of New Mexico is introduced species; the percentage ranges up to 24.8 percent in Missouri, 27.5 percent in Illinois and as high as 47 percent in Hawaii.

Many of the introduced plants, such as corn, soybeans and wheat, are beneficial to the United States. Others, however, pose a threat to the environment and cost billions of dollars to control. Such pests include European purple loosestrife, which now grows in 48 states and costs $45 million a year to control. Leafy spurge can now be found in at least 36 states and causes more than $144 million each year in loss of grazing land in Montana, North Dakota, South Dakota and Wyoming.

Animal pests include the brown tree snake, which has...