Running Wild

It sounds like the plot of a horror movie: Someone dumps a few pet gold­fish into a creek. Flash forward 15 years: The fish have multiplied and spread throughout the region. Their offspring have grown to the size of footballs and consume everything in their paths.

That’s pretty much what’s happening in Western Australia, according to scientists at the country’s Murdoch University. There, supersized goldfish have taken over, destroying native plant and animal species as they search for food in ­rivers and lakes. 

But the problem isn’t unique to Australia. It’s also occurring in the United States and Canada.

The goldfish are just one example of invasive species—organisms that are non-native to an ecosystem and whose introduction causes environmental or economic harm. Today, the threat of invasive species is being felt around the globe.

Species become invasive when they’re introduced to a place without the predators, climate, or diseases that normally would limit their growth. Invasive species can displace or even wipe out native wildlife. In South Florida, for example, marsh rabbits are at risk of disappearing because they’re now prey for an unwelcome newcomer, the Burmese python (see sidebar).

The snakes were originally imported from Asia to be sold as pets. But many escaped from pet stores and home tanks during a hurricane in 1992. Others were released by their owners into swamps—where the pythons now devour even alligators.

Robert M. Nowierski is a pest management expert at the National Institute of Food and Agriculture. He says the threat of invasive species has grown in recent years “with the increasing speed and ease of global trade and intercontinental travel.”

Now that oceans can be crossed in hours instead of weeks, for example, a few stray insects among exported plants or packing materials can live long enough to reproduce in an entirely new environment.

Experts estimate that invasive species cause about $137 billion a year in economic losses in the U.S. alone. Those costs include damage to crops and repairs to infra­structure. In the Great Lakes area, for example, zebra mussels (a mollusk from Russia) have clogged water pipes.

One of the most worrisome invasive animal species is the Asian longhorned beetle. It arrived in the U.S. in the 1990s. Lacking natural predators and with plenty of hardwood trees (such as maples) to feed on, its population here exploded.

“The beetle threatens recreation and forest resources valued at billions of dollars,” says Nowierski. “It has the potential to destroy millions of acres of [trees].”

Once established, invasive species can be hard to eradicate. So in addition to searching for solutions, experts are focusing on prevention.

One such effort is taking place at major international airports, where the U.S. government operates special facilities for checking imported goods. This ensures that they’re pest-free before entering the U.S.

The main thing to remember, experts say, is that even small changes can throw a balanced ecosystem totally out of whack. That’s why they caution against releasing pets into the wild, no matter how small or seemingly harmless.

Take it from Stephen Beatty, a scientist who studied Australia’s giant-goldfish invasion. “Introduced species,” he warns, “can have really unpredictable impacts.”