What is an invasive species?

Invasive species can have positive effects on their new environments, but it is hard to predict the outcome of relocating them.

An invasive species is a plant or animal species that doesn’t naturally occur in an ecosystem, but now is having an impact on native flora and fauna.

These invaders may take over and threaten native species, spread disease to humans, wildlife, and plants, or upset an existing balance between predator and prey.

How many invasive species exist in the United States?

Scientists estimate that in the U.S. alone, about 7,000 invasive species have taken hold. According to the National Wildlife Federation, 42 percent of threatened or endangered native species are at risk primarily because of invasive plants and animals.

What are examples of invasive species in the United States?

Kudzu, a quick-growing vine, was brought to the U.S. from Japan in 1876. This invasive species spread rapidly and strangled native plants by blocking their access to light. Experts estimate that kudzu grows at a rate of 150,000 acres each year and has spread as far as British Columbia in Canada.

Zebra mussels are another example of how quickly an invasive species can take over native habitat. Originally from the Black Sea and the Caspian Sea, they were detected in the U.S. in 1988. The mussels outcompete local shellfish and crowd the water with their shells. They damage harbors and waterways as well as ships and boats, and contaminate water-treatment and power plants. According to the Center for Invasive Species Research at the University of California, Riverside, the cost to manage invading zebra mussels in the Great Lakes alone exceeds $500 million a year.

How do invasive species get here?

Native to Central and South America, the cane toad—an invasive species—wreaked havoc on Australian wildlife after being imported to control pests.

(Photo: Johnny Haglund/Getty Images)

Like kudzu and zebra mussels, most invasive species arrive because of human activities—on ships or planes or as part of misguided human initiatives, such as a program to import cane toads to Australia in the 1930s to control a sugarcane pest. The cane toad instead has spread across the continent, decimating native wildlife.

How is climate change affecting invasive species?

Higher temperatures may open up new territory to invasive species acclimated to warmer weather while putting additional stress on native plants and animals.

Are there any benefits to invasive species?

In 2011, a Conservation Biology paper pointed out that some invasive species do helpful things for the environment and many now-beloved creatures were once invaders. Several species of honeybees were introduced to North America from Europe starting in the 16th century and now pollinate more than 100 crops.

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