The United States Department of Agriculture defines invasive species as species that are “non-native (alien) to the ecosystem”, and that have the potential to “cause economic or environmental harm” as well as harm to humans. Unfortunately, humans play a huge role in transporting these foreign invaders. Read on to see the bizarre creatures coming soon to a backyard near you, and learn about how these animals found themselves thousands of miles from home — and why they’re so dangerous.
1. Northern Snakehead
The film Snakehead Terror premiered on the Syfy channel. The movie was based on a true event in Crofton, Maryland, in which invasive snakehead fish were found in a local pond. While the film, and several films following it, took many creative liberties, the invasion of these foreign fish can become a real-life horror movie for our ecosystem.
Native to China, Russia, and the Korean Peninsula, this large predatory fish has been introduced to other countries. Northern snakehead fish are an important food source in many regions across East Asia, and it’s believed that the invasive species was possibly released to breed it for food. This freshwater fish is extremely adaptive, and an opportunistic feeder. As an aquatic apex predator, it has the potential to wipe out native species, and threaten the commercial fish industry.
2. Red-Eared Slider
The release of the franchise Teenage Mutant Ninja Turtles may have had fans cheering, but biologists weren’t saying “Cowabunga” at the sight of these hard-shelled superheroes. It is believed that the popularity of the series led to an explosion in pet turtle sales. Red-eared sliders, the turtles the cartoons were modeled after, soon became the most widely traded turtle in the world.
Red-eared sliders are native to northern Mexico and the southern United States. Due to their popularity and release into the wild, they have become an invasive species across the world. Though they look small in pet shop windows, these turtles continue growing to up to 13 inches. They compete with native turtle species for food, basking, and nesting sites. Like many reptiles, these turtles can carry the Salmonella bacteria to humans, and larger turtles can bite.
3. Feral Hogs
This little piggy went to the shop, this little piggy went…well, everywhere. Feral hogs are thought to be descendants of Eurasian hogs brought to the United States by Spanish explorers in the late 1500s. These not-so-little piggies soon spread across the United States, where their numbers now range in the millions. Voracious eaters, they’ll feed on anything from roots to the young of endangered species.
While large apex predators disappear from the North American ecosystem, these ferocious pigs have multiplied. Their habit of digging up roots costs millions of dollars in agricultural damage. They are also vectors for a variety of dangerous pathogens that can cause swine fever, foot and mouth disease, influenza A, and even tuberculosis. The pigs are also violent towards humans, mauling a Texan woman to death in 2019.
4. Giant African Snail
Looking like a creature out of a horror movie, the giant African snail has slowly oozed its way into North America. Native to West Africa, the snail was first spotted in the 1940s, stashed in the cargo hold of a boat. The snails have continued to enter, either by hitchhiking in cargo or through the exotic pet trade.
These giant snails, which can reach lengths of eight inches, pose a threat to agriculture. Populations have already established themselves in Florida and across the country. Snail infestations can quickly devour and destroy crops: according to the USDA, had the population of snails not been controlled, Florida could have lost $11 million a year. The snail is also a vector for the rat lungworm, a parasite which can cause esosinophilic meningitis.
5. Nile Monitor Lizard
Florida is already home to some of America’s largest reptilian predators, but in the past few decades, a new reptile came to town: the Nile monitor lizard. Able to grow up to eight feet in length and armed with sharp talons, this newcomer is causing fear in the environmental community. Many believe that the lizards found in South Florida are the result of the exotic pet trade.
Monitor lizards are at home in tropical climates, and are adept swimmers, making it easy for them to navigate the network of canals and lakes across Florida. These carnivorous reptiles feed on anything they can catch, and have been implicated in the disappearances of many family pets. Nile monitors are aggressive, and can use their talons and whiplike tails to defend themselves. In one gruesome 2002 case, a man was found eaten by his pet monitor lizards.
They may look beautiful, but don’t touch. These ornate marine fish are covered in venomous fins. Native to the Indo-Pacific region, this invasive species has spread across the world. Many theories have arisen over how these fish made their way to the waters off the United States, but many point to the exotic fish trade. Because of their venomous spines, hidden behind their delicate fins, this invasive species has few predators.
This venom can cause extreme pain and even death, making them dangerous to divers and fishermen who may come in contact with them. Like their namesake, lionfish are aggressive hunters. They can negatively impact the delicate balance of the coral reef ecosystem by preying upon fish that maintain coral health. Communities across the Caribbean have attempted to control the population by holding bounties, hunting events, and even eating them.
7. Cane Toads
Originally imported to reduce agricultural pests in sugarcane crops, the cane toad has proven to be one of the most widespread invasive species. Considered the world’s largest toad, the frog is native to Central and South America, but has spread across the world.
Growing up to ten inches long, they feast on small rodents, insects, birds, bats, and anything else they can fit in their mouth. These toads also hold a deadly secret: their skin is lined with deadly poison glands. Every year cane toads kill countless animals, including pets that attempt to eat the poisonous toads. Their presence in ecosystems is correlated with a loss of predatory animals, making biologists consider them one of the most dangerous invasive species.
8. European Starling
It is rumored that in 1890, a flock of birds was released by a man attempting to introduce the bird species mentioned in William Shakespeare’s work to North America. Unfortunately, this prolific bird has caused somewhat of a Shakespearean tragedy for the environment.
Not only are these birds noisy, but droppings from their large roosts, which can hold 1.5 million birds, can kill trees due to large concentrations of chemicals in the bird’s waste. The birds also compete with native species for nesting holes, threatening their ability to reproduce. The birds cause hundreds of millions of dollars in damage to agriculture by devouring crops and spreading weeds through seeds found in their droppings.
9. Brown Tree Snake
Although this snake make look like a cartoon character, its impact on the environment is no laughing matter. The arboreal snake is native to Papua New Guinea, coastal Australia, eastern Indonesia, and Melanesia. Following World War II, the brown tree snake made its way to the American Pacific island territory of Guam, presumably in the cargo hold of a ship or plane.
The venomous — and hungry — snakes have caused an environmental emergency on the island, where they have wiped out most of the island’s small vertebrate species. They have caused more than twelve bird species to go extinct, and their preying on pollinators like fruit bats and birds is also affecting the flora of the island. Brown tree snakes show us quite viscerally the damage an invasive species can do to every aspect of an entire ecosystem.
10. Asian Giant Hornet, aka ‘Murder Hornet’
In early 2020, media outlets reported that a dangerous insect called the ‘murder hornet’ had arrived in the United States. This large insect, known as the Asian giant hornet, is the largest of its kind in the world. It is native to East and South Asia, and the Russian Far East. Sightings in late 2019 in the Pacific Northwest have caused scientists to sound the alarm over this possibly dangerous invasive species.
The giant hornet can grow up to two inches long, and possesses a stinger a quarter of an inch long. Stings from multiple hornets can be deadly; in 2013, 41 people were killed in China. These ‘murder hornets’ are not only a threat to humans, but they threaten honeybee populations. Hornets are adept bee eaters and killers. Bee populations, which are already suffering, could become extinct with the proliferation of these predatory hornets.
11. Zebra Mussels
Despite being the size of a fingernail, zebra mussels have managed to create a huge economical, and environmental, disaster. These striped mollusks are believed to have entered the United States in the ballast water of cargo ships arriving from their native homes in Eurasia. This population quickly spread from the Great Lakes region across the United States, leaving a path of destruction in their wake.
Zebra mussels are dangerous to local species. They filter out useful algae other species use for food, and they attach themselves to other native mussels, eventually killing them. As filter-feeders, they accumulate large amounts of toxins resulting in them harboring avian botulism, which has killed thousands of birds. In dense populations, they can block pipelines and damage hydroelectric and water-treatment facilities. It is estimated that they have cost power companies over $3 billion.
12. Walking Catfish
This species of freshwater catfish gets its name from its purported ability to “walk” on land. While it doesn’t truly walk, the fish is able to use its pectoral fins and a wiggling motion to help it navigate dry land. Like other air-breathing fish species, the walking catfish has a specialized organ to take in oxygen, as it moves from one source of water to the other.
Walking catfish are native to Southeast Asia, where they are an important food source. It is believed that the fish populations in Florida are the result of the aquaculture and fish farm industry. Able to grow up to 20 inches, these fish are powerful predators, with voracious appetites. They have been known to enter commercial fish farms and deplete the pools of fish. For this reason, they are considered a dangerous invasive species.
13. Emerald Ash Borer
Looking at an emerald ash borer, many people would be surprised to know that this tiny beetle has been responsible for killing millions of trees across North America. This jewel-toned beetle is native to Northeast Asia, and arrived in North America as a stowaway in imported wood products.
This invasive species lays its eggs between layers of bark and crevices in ash trees. The larvae that hatch begin to feed on the inner bark, preventing the tree from being able to transport water and receive nutrients. These once-healthy trees soon die, severely impacting the ash wood product industry. Costs to remove dead and dying trees will likely cost local governments billions of dollars over the next decade.
While nutria are often confused with native muskrats, these South American visitors have overstayed their welcome. These large rodents were introduced to the United States during the late 1800s as a potentially lucrative fur-producing animal. While the fur industry enjoyed some success, by the 1940s most of the nutria imported were released accidentally, or intentionally in order to control aquatic vegetation.
Today, these rodents, which can weigh up to 20 pounds, have turned American ecosystems into an all-you-can-eat buffet. Nutria feast on vegetation to the point where the soil becomes eroded and bare. Their appetite has resulted in the destruction of vital wetlands and marshes, and has also made nearby areas more susceptible to flooding or structural damage. Nutria also are hosts for dangerous illnesses like tuberculosis, and carry tapeworms, which can contaminate water supplies and pose a danger to swimmers.
15. Monk Parakeet or Quaker Parrot
Despite having a holy name, this small parrot is anything but saintly. Native to South America, the colorful monk parakeet made its way into North America through the pet trade. Escaped parrots have quickly colonized their new environment, and are now found across the continent.
One of the reasons why this parrot has been so successful is that unlike other parrot species, monk parakeets build stick nests instead of using tree holes. Often large and heavy, most stick nests are constructed in trees, or on man-made structures. Some nests have been reported as weighing 400 pounds. If situated by electrical lines, utility poles, and electrical transformers, they have the potential to cause power outages and fires.
16. Javan Mongooses
This proficient little hunter made its way from Asia to the tropical paradise of the Hawaiian islands as part of an attempt to control pests on sugar plantations. With the increase in sugar plantations came an increase in rats or other pests. In the late 1800s, mongooses were exported from India to plantations across Hawaii.
While the mongooses kept up their part of the deal by reducing rats, they developed a taste for local native birds and the eggs of endangered sea turtles. On other islands, this small predator is responsible for the extinction of ground-nesting birds and small native snakes. According to the Hawaiian government’s website, damage to Hawaiian and Puerto Rican environment by mongooses was estimated to $50 million in 1999. Today, only two Hawaiian islands, Lanaʻi and Kauaʻi, are free of mongooses.
17. Asian Carp
One group of fish that have scientists and fishermen concerned are Asian carp. Originating in Asia, this fish group is made up of the species bighead carp, black carp, grass carp, and silver carp. These were imported as a way to control aquatic vegetation growth, treat sewage, and curb parasite growth.
Unfortunately, these fish found themselves in the Mississippi River, which they then used to spread across the country. Often weighing more than 100 pounds, they can easily overtake smaller fish in competitions for food and habitat. They can make the water quality poor enough to kill more sensitive species. Carp can leap over barriers and low dams, making it even easier for them to spread. Their tendency to “jump” out of the water has even injured boaters and fishermen.
Florida’s many waterways and warm climate have made it an ideal home for many invasive fish species. One family of fish that have taken over in a relatively short period of time have been cichlids. These fish are native to Mexico and Central America, but have been exported around the world as pets.
It is believed that most of the cichlids found in the United States are the result of the aquatic pet trade. These fish often display aggressive behavior and are extremely territorial. Biologists worry that these predatory fish will reduce native fish populations as they compete over territory and food. The Mayan cichlid, in particular, worries biologists because it is now one of the most commonly found fish in some canals in the Everglades.
19. Spectacled Caiman
As the alligator trade became prohibited in the 1950s, pet salesmen introduced an equally scaly replacement: the spectacled caiman. Native to Central and South American, this crocodilian has moved in alongside his Floridian relatives, the alligator and the American crocodile. Researchers have found breeding populations across southern Florida, fueling fears that the spectacled caiman can potentially disrupt the local environment.
Because they live in the same environment as Florida’s native crocodilians, competition can ensue over food, breeding grounds, and other resources. Smaller than alligators and crocodiles, caimans feed on fish, birds, small reptiles, and mammals. Their appetite can threaten native species’ populations. In some instances, local fish have been infected with caiman tongueworms, parasites carried by the large reptile that endanger other fish, alligators, and crocodiles.
20. Asian Long Horned Beetle
First observed in the United States in 1996, this spotted beetle is actually native to eastern China and Korea. Researchers believe that the invasive species was accidentally introduced into the country from infested wood packaging material. This tree-destroying pest feasts on native species such as birch, ash, maple, and willow trees.
These beetles lay their eggs in the bark of trees. As the larva develops, it continues to consume the tree from the inside out. It is estimated that the destruction of trees by this beetle can lead to $669 billion in losses. Warehouses that house wood material are very susceptible to infestations, and scientists are working hard to reduce current populations, and prevent entry of new beetles into the United States.
21. Coquí Frog
While this little frog may be a beloved unofficial symbol of Puerto Rico, Hawaiians have no love for this invasive amphibian. Native to Puerto Rico, the coquí frog has spread to Florida and Hawaii, likely hidden in exported potted plants. These crooners are known for their loud calls, and have become a nuisance animal. Prospective homeowners refuse to buy homes in coquí territory.
Hawaii’s large plant industry has also suffered because customers are unwilling to buy potted plants that may be harboring these loud creatures. While the frogs are tiny, they exist in such dense populations that one group can eat over 300,000 invertebrates nightly. Their nocturnal gorging can threaten local insect populations, particularly pollinators. Hawaiians worry that these tiny, but disruptive, frogs can negatively impact property values and even their economy.
22. Green Iguanas
Driving past the many canals that run through South Florida, it isn’t uncommon to see groups of iguanas grazing alongside the road. While they may look harmless as they munch away on plants, this invasive species is becoming a major threat to Florida’s environment. These dinosaur-like green lizards are native to Central and South America, but their popularity as pets could be why they are now found throughout Florida.
These herbivores can not only damage your garden, but entire infrastructures too; their burrows can destroy building foundations, collapse sidewalks, and erode seawalls and canal banks. These brightly colored reptiles can grow up to six feet long, and are armed with sharp claws and a tail that can be used as a whip. Like many other reptile species, they can also harbor the salmonella bacteria.
23. Rhesus Macaques
In the 1930s, a man named Colonel Tooey came up with a wild idea to improve his boat tours. The Florida cruise boat captain decided to import six rhesus macaques, which he released on an island near Silver Springs, Florida. Unfortunately for Tooey, rhesus macaques are adept swimmers, and the troop of monkeys quickly escaped to nearby Silver Springs State Park.
Native to Central, South, and Southeast Asia, the monkeys are perfectly at home in Florida’s year-round warm climate. While park visitors find the monkeys adorable, scientists worry that the increasing population can be dangerous. Rhesus macaques can grow to be large, and potentially aggressive, animals. This population is also infected with the herpes B virus, which can infect humans as well.
24. Argentine Black and White Tegu
Another South American visitor which came to stay in South Florida is the Argentine Black and White tegu. This large speckled lizard is commonly imported through the exotic pet trade, and the breeding populations found today may be descendants of released or escaped pets.
The omnivorous tegu can grow to be five feet long. Eggs are a favorite for the lizard, and tegus have been spotted eating the eggs of ground-nesting birds, turtles, alligators, and endangered gopher tortoises. Scientists worry that their dietary habits can negatively impact egg-laying endangered species. The lizards can be aggressive, delivering a painful bite with their sharp teeth and strong jaws. Other tegus — gold tegus and red tegus — have also been reported stalking their new North American home.
25. Burmese Python
In the past few years, grisly photos showing alligators and giant Burmese pythons fighting to the death have made front pages. Native to Southeast Asia, these giant snakes were first spotted in Florida in the 1990s. Since then, their population has exploded, causing great concern over how these snakes may affect Florida’s ecosystem. Reaching lengths of almost 20 feet, this apex predator can eat a variety of wildlife.
Scientists have uncovered a link between a decline in mammals and an increase in pythons. Most live in the Everglades, where they pose a huge threat to indigenous species, even to large animals such as alligators and Florida panthers. Because the Everglades is a conducive habitat for the snake, herpetologists estimate that there may be anywhere from 30,000 to 300,000 hiding in the murky waters of the swamp.