Most Damaging Invasive Species in U.S.

Animal invaders have bridged oceanic gaps for centuries—some stowed away in ship-ballast water while others were intentionally lugged over by the overzealous, either to solve a pre-existing problem or just for aesthetic pleasure. However, sometimes a seemingly benign introduction creates environmental travesty and ecosystem despair. Here are the most damaging animals ever to enter U.S. soil.

Big constrictors squeeze the life out of mammalian prey and ecosystems. The U.S. Geological Survey says nine species of pythons, a type of snake that can range from 12 to 28 feet in length, pose a medium- to high-risk threat to ecosystem health. Over the past 30 years, these weighty reptiles have been traded domestically and internationally, and pet owners often take these snakes into homes that cannot accommodate them as they grow. When the snakes get too big, offending owners release them into the typically Floridian wild, where they ingest endangered species like the Key Largo wood rat and invade wildlife refuges. Under the Lacey Act, the U.S. Fish and Wildlife Service proposed to stop constrictor serpent imports into the country and even ban transport between states.

Asian Carp
Many injurious invasives come by water. Asian carp—including the common, black and bighead variety—were brought to the U.S. in the 1970s as live vacuum cleaners meant to remove algae and suspended matter from ponds. These fish can grow to 100 pounds and will eat just about anything, adapting shockingly well to new environments. They have taken over and now represent 90 percent of the biomass in the Illinois River. Researchers worry that these ravenous, opportunistic fish will reach the Great Lakes and cause real problems to the fragile ecosystem—virtually eliminating biodiversity.

Zebra Mussels
Zebra mussels originally smuggled their way into the U.S. in the ballast water of boats and have clogged the inside of pipes since the 1980s. These are no minor pipe blockages—these clogs total billions of dollars in fixes. And the mussels cling to more than pipes. They adhere to motors and to other native mussels, wreaking havoc for boat owners and decimating indigenous wildlife. So many zebra mussels exist in the Great Lakes, constantly filtering water, that they've changed the water from murky to clear, fiddling with the careful ecosystem balance. With clearer water, more sunlight reaches the bottom of the lakes where organisms thrive on darkness and can't live in the light.

The small Indian mongoose, reaching no more than a foot or two in height, was originally brought to Puerto Rico and the Hawaiian islands to protect sugar cane fields from rat and snake damage. But instead of acting as an aid for crowd control, the mongoose quickly became a hindrance, harming far more wildlife than anticipated. Now fully settled in Hawaii, the agile creature preys on birds and small reptiles, which injures both the poultry industry and game hunters and costs the island nations $50 million dollars in damages a year. The mongoose has so far caused the extinction of 12 reptile and amphibian species from Puerto Rico, the West Indies and Jamaica.

This innocuous, petite speckled migrant came to the U.S. in the late 1800s as part of a misguided attempt to introduce the animals mentioned in Shakespeare's works to America. Like Shakespeare's works, European starlings stuck in the U.S. and disseminated outward from New York City, where they originally arrived. Now starlings occupy most of North America, steal nesting sites from other birds and rob the agriculture industry of $800 million dollars annually by damaging fields. To make matters worse, starlings spread diseases that infect both humans and livestock, costing a further $800 million a year in healthcare.