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The dirty dozen: 12 of the most destructive invasive animals in the United States

For some animals, there’s no such thing as a dog-eat-dog world. They rule.

Animals from around the world that stow away in airplanes, ships and the luggage of some smuggler become almost bulletproof when they make their way into the American wilderness as invasive species. Why? They’re new here, and they don’t have predators to keep them in check. Animals that should be afraid of a vicious predator aren’t. Invasive species eat like kings.

Living high on the hog, these marauders aren’t going anywhere. Unlike many native animals that are disappearing from North America — vaquita porpoises, monarch butterflies, bottlenose dolphin and such — invasive species are growing faster than wildlife and game officials can manage them. In many cases, authorities have given up any hope of eradicating them.

Here are 12 of the most destructive invasive plants and animals in the United States, a dirty dozen. If it’s on this list, there’s a good chance that a government official in an office somewhere is trying to think of ways to kill it.

Burmese pythons

These long, lean eating machines are terrorizing the Florida Everglades. Humans don’t have much to fear, but native animals had better watch their backs. Alligators are being knocked off their perch as the swamp’s top predator. People ask why these snakes are such a problem. Why can’t experienced hunters walk into the Everglades and kill them? Burmese pythons from Southeast Asia are so stealthy that even experts with the Florida Fish and Wildlife Conservation Commission have a tough time spotting them, let alone killing them. Since they were determined to be established and put the squeeze on the swamp in 2002, deer, raccoon, marsh rabbits, bobcats and possum have declined by as much as 99 percent in some cases, according to researchers for the U.S. Geological Survey.

Emerald ash borer

This bug’s march across the Midwest is not the kind of green movement that conserves nature. It ruins ash trees that provide durable wood used for flooring, bowling alleys, church pews, baseball bats and electric guitars. The bugs sparkle like a jewel with their glittery hide, but the nickel-sized holes they bore into trees are ugly, and the squiggly trails their larvae etch on the bark can make your skin crawl. They arrived in southeastern Michigan in 2002 from their native habitats in Russia, China and Japan. Since then, tens of millions of ash trees have been killed, and their numbers continue to grow.


The official name comes off like some kind of vitamin drink, so Louisianans came up with another that sounds more fitting: swamp rats. Nutria don’t just look like rats with long tails and orange buck teeth, they breed like them. Female nutria give birth to litters of up to 14 then go back into heat in two days. Federal wildlife officials say there’s no hope of eradicating them from Louisiana, where they were imported from South America for their fur in the 1930s and grew out of control after being released when the industry died. A Chesapeake Nutria Eradication Program is working furiously to push them off the Del Marva Peninsula and wipe them out in Maryland and Delaware. Their endless digging on the banks of rivers rips up plants by the root, causing soil to erode, destroying native habitat for everything from muskrats to crabs to juvenile fish.

European starling

Starlings are little birds that travel in huge packs, and they are known for wreaking havoc. Birders don’t like it, but starlings are generally regarded as pests. Every year, the Agriculture Department’s division of Wildlife Service’s kills 4 million animals identified by residents across the country as a nuisance, and starlings are targeted the most — by far. Moving in flocks that resemble small black clouds, they descend on cities, towns and mostly farms, beaks aimed at the ground in search of food. Starlings are known to swarm toward feeding cattle to steal their food, needling and harassing the bigger animals until they back off. Since their introduction to the United States by Shakespeare enthusiasts in the 1890s, they have become arguably the most successful foraging bird in the country, with a population of about 200 million.

Northern snakehead

It’s called a snakehead. That dreadful name pretty much sums up the most feared fish in the Chesapeake Bay watershed, a sharp-tooth monster so scary that fishing tournaments are held not to eat, or fight it on the line, but solely to kill it. Snakeheads look like some weird cross between a python and an electric eel, and attempts to get large numbers of people to fish and eat it so that snakeheads don’t eat too many other creatures in the estuary have failed. Stories about how this fish from China and Korea ended up in the bay in the early 2000s vary. Some say a clueless aquarium dumped several in a tributary; others say someone carried them from a fish market. Whatever happened, female snakeheads, which are baby factories known to carry up to 100,000 eggs, took it from there and have now spread to Delaware and Virginia.

Brown marmorated stink bug

Here’s a quick thought, in 10 words: A stink bug is probably in your house right now. They don’t seem to mind that you’re there. They just need a place to rest through winter and crawl out in spring to mate and make millions more stink bugs. Stink bugs annoy because they swarm and smell like cilantro, but they don’t bite or carry disease. They’re not to be confused with the growing swarm of Asian kudzu bugs in Georgia, although their behaviors are similar. Stink bugs destroy fruits and vegetables and drive up produce prices. They first showed up in Allentown, Pa., in 1998 after crawling out a cargo ship that probably stopped in China, their native land. There, stink bugs aren’t a problem because small wasps lay eggs on their backs and the babies use them for a meal as they grow. With no wasps in the mid-Atlantic, they became marauders.

Feral hogs

They have razor-sharp teeth, curling tusks and are so hot tempered that they charge humans. Otherwise, feral hogs, wild pigs or big boars are just farm pigs gone wild. They’re established in 47 states, with massive populations in Texas, Florida, Georgia and North Carolina, and a growing one in Virginia. In most of those places, experienced hunters have a green light to shoot them on sight. Here’s why: They cause about $1.5 billion in damage nationwide each year. They’re also an ecological nightmare that eats turtle eggs, wild turkey eggs and quail that nest on the ground. Acorns and chestnuts that are the next generation of trees go into their stomachs. Feral pigs were introduced to the United States from ships centuries ago, but the recent population boom, state game officials and biologists say, is largely the fault of hunters who imported wild pigs to hunt year round.


Lionfish are very pretty. That ends the positive vibrations that marine biologists give this animal. They are exotic gluttons that eat everything they can stuff in their mouths, and they are destroying life on the coral reef that serves as habitat for thousands of species of other fish. That’s how they earned the name Norway rats of the Atlantic. Lionfish are native to the Pacific Ocean, but they were widely traded for their looks and were first spotted near Miami in the mid-1980s before proliferating in the Gulf of Mexico, the Atlantic and the Caribbean Sea near the turn of the century.

Norway rat

Norway rats have lived in the United States for so long that they’re like family. They were introduced in 1775 and are now everywhere, including Alaska and Hawaii, living under various aliases, including brown rats and sewer rats. Norway rats prefer to live near humans and they like choice meats, but really a rat will eat anything — eggs, young chickens, vegetables, garbage and wood. They’re a menace known to climb trees and skitter across thin branches to kill and eat wild chicks in their nests. They’re survivors, adept at avoiding things that eat them.


Tegus look like little brown anolis lizards — on steroids. They’re muscular, fast and love eggs. They’re known to harass pets — some reports claim they have killed cats — and they invade homes. Tegus were brought to the United States as pets, and are still available for sale in some stores. They were released into the wild and have spread from the Florida Keys to the Florida Panhandle and are threatening to reach into southern Georgia. Like pythons, Florida officials have launched offensives designed to kill them. And also like pythons, those efforts have failed. There are now so many that Florida game officials have given up on the idea of eradicating them, and now only hope to manage the population.

Asian citrus psyllid

It’s a little farfetched, but this tiny bug could be the end of Florida orange juice. The Asian citrus psyllid carries a bacteria that goes by many names: huanglongbing, “yellow dragon disease” and “citrus greening.” But what people remember is that Florida orange growers, agriculturalists and academics compare it to cancer. Roots become deformed. Fruits drop from limbs prematurely and trees die. Half of all citrus trees in Florida, which provides 80 percent of the nation’s orange juice, are infected. The trees slowly die. Florida, which provides up to 80 percent of U.S. orange juice, has been hardest hit, but the psyllid and disease have been detected in Georgia, Louisiana, Texas and California, which provide most of the nation’s lemons. Psyllids were first detected outside Miami in 1998 and the bacteria was discovered near there in 2005. It spread to 31 other counties within two years.

Brown tree snake

Brown tree snakes are not in the contiguous United States. Be happy about that. Hundreds of thousands are in Guam, a U.S. territory, and are responsible for the decimation of birds there. Birds had no reason to fear an animal that didn’t exist until it was introduced accidentally in the 1950s. Brown tree snakes are so out of control that they’re known for causing power outages when they climb utility poles. Now that many of the birds are gone, the snakes have turned their attention to native lizards. Hawaii, 3,800 miles east of Guam, is on high alert to stop the poisonous, predatory snakes native to Australia and Indonesia.