What kinds of invasive species can you find in the United States?

Animals that are not native can cause many problems. They put a lot of pressure on native species as they compete for food, territories, and nesting areas.

Below, you will learn about an array of different invasive creatures, along with the myriad of problems they cause!

29 Invasive Animals Found in the United States:

Just a quick note: you won’t find any insects or fish below. Those articles are coming soon!

#1. Rock Pigeon

• Columba livia

These invasive birds are extremely common in the United States but are almost exclusively found in urban areas. Rock Pigeons are what everyone refers to as “pigeons.” You have probably seen them gathering in huge flocks in city parks, hoping to get tossed some birdseed or leftover food.

The typical pigeon has a gray back, a blue-grey head, and two black wing bars. In addition, look for a green and purple iridescence around their necks!

Rock Pigeon Range Map

Love them or hate them, Rock Pigeons have been associated with humans for a long time! Some Egyptian hieroglyphics suggest that people started domesticating them over 5,000 years ago. But, interestingly, scientists aren’t even sure where their original range occurs!

#2. European Starling

• Sturnus vulgaris

• They are about the size of an American Robin. Their plumage is black and appears to be shiny.
• Breeding adults are darker black and have a green-purple tint.
• In winter, starlings lose their glossiness, their beaks become darker, and they develop white spots over their bodies.

Despite being common, European Starlings are an invasive species in the United States.

Back in 1890, one hundred starlings were brought over from Europe and released in New York City’s Central Park. The man responsible (Eugene Schieffelin) had a mission to introduce all of the birds mentioned in Shakespeare’s plays in North America.

European Starling Range Map

The rest is history as starlings easily conquered the continent, along the way out-competing many of our beautiful native birds. Their ability to adapt to human development and eat almost anything is uncanny to virtually no other species.

Here’s something amazing about these non-native birds:

It’s the magical way they travel in flocks, called murmurations. Check out the video below because it’s mesmerizing.

#3. Wild Boar

• Sus scrofa

• Adults range from 5 to 8 feet in length and weigh between 145 and 600 pounds.
• Their thick, coarse hair ranges in color from black to reddish-brown.
• Males have large canines that protrude from the mouths of adult males.

Wild Boars are invasive mammals in the United States, as they were introduced from overseas. Their population has exploded in the last 50-100 years, leading wildlife departments to implement population control programs.

Because of their aggressive nature and lack of fear, Wild Boars can be dangerous to livestock, humans, and pets. If you have a Wild Boar on your property or see one while you’re out and about, call your local animal control office for advice. Don’t try to approach this unpredictable animal!

They are omnivores, and what they eat varies with season and location. Wild Boars consume large amounts of plant matter, including fruits, nuts, roots, herbaceous plants, and crops. Their voracious appetite can be very detrimental to an ecosystem, causing a loss of plant diversity and extensive soil erosion.

Interestingly, these birds are invasive to the United States.

Unfortunately, somebody introduced Eurasian Collared-Doves to the Bahamas in the 1970s, and since then, they have rapidly spread. In fact, their population is still spreading!

#5. Mute Swan

• Cygnus olor

• A huge white bird with a long white neck.
• Look for the distinctive orange bill that features a black base and knob.

Mute Swans are among the most elegant and beautiful birds you will see in the water. They are also enormous and are one of the heaviest birds that can fly!

But did you know that Mute Swans are NOT native to the United States?

Due to their beauty, Mute Swans were imported from Europe and released in parks, large estates, and zoos. Unfortunately, these individuals escaped and have established an invasive wild population.

Don’t be fooled by their appearance; these invasive animals can be aggressive and regularly attack kayakers and other people who get too close to their nest. They also displace native ecosystems due to their voracious appetite, which requires up to 8 pounds (3.6 kg) of aquatic vegetation daily!

Despite their name, these swans are not mute!

While relatively quiet, they make a hoarse trumpet sound when defending their territory. And if they are threatened, expect to hear various barks, hisses, and snorts.

#6. House Sparrow

• Passer domesticus

House Sparrows are an invasive species that originated from the Middle East. But now they are one of the most widespread birds in the United States (and the world)!

House Sparrows owe their success to their ability to adapt and live near humans. Because of this, they are almost always found in urban and suburban areas.

Range Map – House Sparrow

House Sparrows can be heard across the entire planet. Pay attention the next time you’re watching the news in another country. Listen for a simple song that includes lots of “cheep” notes.

#7. Nutria

• Myocastor coypus

• Has two very large, yellowed incisor teeth. 
• Has a long, thin tail with no hair on it. 

Nutria look like a combination of a beaver and a muskrat. They live near waterways in burrows, and their native range is tropical and temperate South America. 

Nutria were intentionally introduced to North America in 1889 by fur farmers. Over the years, many individuals escaped and eventually established a wild population.

Nutria Range Map

These invasive animals cause many problems in the United States!

Because Nutria devour so many plants daily, they cause irreparable damage to wetlands and marshes. Their prolific eating habits also cause direct conflict with humans. They are known to destroy crops such as rice, corn, sugar, and many others.

The burrowing behavior of Nutria also harms the ecosystem. The burrows weaken the structure of the ground they dig into. Nutria burrows inadvertently cause damage to human structures, such as roads, dams, and flood defenses. 

Lastly, Nutria carry several diseases that can make humans ill. Tuberculosis, septicemia, and various parasites can pass from these rodents to humans. The presence of Nutria in a waterway can make swimming in or drinking the water dangerous. 

#8. House Mouse

• Mus musculus

• The tails are hairless and can be as long as their bodies.
• House Mice are smaller and lighter built than rats.
• They usually have light brown fur and large round ears compared to their heads, which give them a cute look.  

These invasive rodents originated in Asia but can now be found across the United States. House Mice arrived in North America on ships in the 1600s and quickly multiplied. 

Mice have dispersed across the planet incredibly successfully, second perhaps only to humans. The biggest key to their success is their ability to adapt their behavior quickly and breed prolifically.

House Mouse Range Map

Salmonella and parasites are the most prevalent illnesses that mice transmit to humans by contaminating food. However, this risk has been greatly reduced through modern food management techniques in the USA. 

House Mice also greatly impact the ecosystems that they invade. They are omnivorous and will devour plants and target animal species that have not adapted to fighting them off. 

Fascinatingly, House Mice also cause the decline of native species by bolstering the health of predators through seasons when other prey would have been hard to find. By becoming prey themselves, the mice inflate the populations of predators year-round. 

#9. Brown Rat

• Rattus norvegicus

Look for Brown Rats anywhere people are living, particularly in urban environments. They’re best known for living in sewer tunnels and subway systems, scavenging food from the trash.

Believe it or not, this small species isn’t native to the United States. It’s thought to have originated in China and Mongolia.

It’s a misconception that Brown Rats spread bubonic plague. In actuality, it’s more commonly spread through ground squirrels! Regardless, they can transmit infections of many kinds, as their blood can carry several diseases.

#10. Black Rat

• Rattus rattus

Interestingly, the Black Rat is an invasive species in the United States.

It’s thought it came from India and was transported to North America on cargo ships. They are now so widespread that it’s considered “naturalized.”

Black Rats are a pest in the agricultural market because they feed on various crops. Like other rodents, they can carry pathogens in their bodies. While they may not appear sick, they can spread infections like toxoplasmosis, typhus, and bubonic plague.

The Brown Rat has taken over many areas where the Black Rat was once the dominant species. Black Rats are slightly smaller and reproduce less often, two reasons this species isn’t as widespread as Brown Rats.

#11. Barbary Sheep

• Ammotragus lervia

• They best resemble large, brown goats. 
• Short brown hair, long necks, and agile, muscular bodies. 
• They have large horns curling back from their heads and long hairy patches on their chests. 

Barbary Sheep are native to Northern Africa. They are especially well adapted to living in arid regions. For example, they don’t have to drink and can take all of their hydration needs from the food they eat.

Barbary Sheep were intentionally introduced to areas of the USA in the 1950s to become exotic game for people to hunt in parks and estates. However, they easily outcompeted native species for resources and proliferated quickly. These invasive animals adapted well to the arid, rocky deserts of the Southwest United States. 

The primary issue that Barbary Sheep cause in the United States is outcompeting the native Desert Bighorn. Barbary Sheep reproduce quickly and are very hardy, suffering low mortalities. They are also prolific grazers.

Secondly, Barbary Sheep appear to have been carrying and transmitting mycoplasma ovipneumoniae to the native Bighorn sheep. This bacterial infection is often fatal for Bighorn Sheep and has caused a large number of deaths.

#12. Sika Deer

• Cervus nippon

• These deer retain their spots from infancy into adulthood. 
• Their coats are usually red-brown, with white spots. 
• Males have thick, upright antlers. Females have short black nubs instead. 

Sika Deer are medium-sized deer that originated in Asia. They can be found naturally in dense forests, where they graze in clearings during the day. As a result, they are often found near humans.

Sika Deer were first introduced on James Island in Maryland in 1916. These individuals were most likely introduced to James Island for the purpose of sport hunting. At that time, the native species, White-tailed deer, had been hunted heavily, and the population was very low. 

These invasive animals often cause extensive damage to crops in the United States, such as soybeans and corn. Their population has exploded, and some farmers compete with deer populations at 3 or 4 times what they can comfortably co-exist with. 

#13. Spotted Deer

• Axis axis

Also called Chital Deer or Axis Deer.

• Golden brown with clearly defined white spots. 
• Their bellies, throats, and the insides of their legs and tails are white. 
• Males are larger than females, and only males have antlers.  

Spotted Deer are fairly large and retain their spots into adulthood, which is unusual among deer. Naturally, they are found in India and nearby countries. 

In 1932, Spotted Deer were transported to the mainland USA and released in Texas. The purpose was to increase hunting opportunities. Initially, they were confined to farms and estates. However, some have since escaped and established large feral populations. 

They graze extensively and prefer the nutritious shoots of young seedlings and saplings. Consequently, their eating habits can destroy many kinds of crops, wild plants, and even large trees.

These invasive animals have caused problems in Texas, such as damaging crops and devastating large areas of virgin forest, dramatically altering and damaging the ecosystem. 

#14. Ring-necked Pheasant

• Phasianus colchicus

• Males have tawny bodies, shiny green heads with red wattles, and a white ring at the base of the neck.
• Females are smaller and are tawny brown all over, with dark brown patterning.
• Both have extended tail feathers, though males are longer. 

Ring-necked pheasants are eye-catching birds that are native to Asia. They are usually found in woodlands and grasslands.

These birds were intentionally imported and introduced to the USA in 1881. In fact, they have been here so long that most people have no idea that Ring-necked Pheasants are not native to the United States!

Ring-necked Pheasant Native  and Introduced Range Map

Ring-necked Pheasants cause issues for native ecosystems in several ways. First, their breeding success and population growth put a strain on habitat and food availability. Ring-necked Pheasants outcompete native birds for limited resources. Pheasants can even be openly aggressive towards other birds. 

Second, the breeding behavior of Ring-necked pheasants leads to them parasitizing nests, directly causing the mortality of native hatchlings. Pheasants nest on the ground, close to other species. Sometimes, they lay their eggs in the nests of other birds. 

#15. Mediterranean House Gecko

• Hemidactylus turcicus

• 1.5 to 2.5 inches long.
• The pupils are vertical, and the eyes are large and round with immovable eyelids.
• This species has two color phases for camouflage.
  • Pale phase: the coloring is light pink to pale yellow or white with brown or gray blotches.
  • Dark phase: the coloring darkens to gray or brown, obscuring the blotches on the back.

You might be surprised that this gecko in the United States is NOT native! The Mediterranean House Gecko was introduced via imported plants carrying their egg clutches. They’re adaptable to so many environments that their population quickly outpaced any of our native geckos!

Mediterranean House Geckos are nocturnal, but this won’t stop you from being able to find them. They’re considered an “urbanized” species, which means they’re just as happy to live inside your house as they are in the wild!

Virginia Herpetological Society

In addition to being comfortable around humans, Mediterranean House Geckos are some of the most vocal lizards around. The mating call of males is a series of clicks, and they frequently make a squeaking noise if threatened.

#16. Egyptian Goose

• Alopochen aegyptiaca

• Despite being a duck, the Egyptian Goose is 24-29 inches (61 to 74 cm) tall and more goose-like in its build.
• The Egyptian goose is colorful and widely valued as an ornamental duck.
• Its body is a pale golden-beige overall, with bright pink legs and brown circles around each eye.

Egyptian Geese are not native to the United States!

These water birds originate in Central and Southern Africa. They were imported to the USA since at least 1904. Naturalized breeding colonies can be found in California, Florida, and Texas.

Male and female Egyptian Geese look very similar. Females are often smaller than males, but otherwise, there is not a lot of sexual dimorphism.

However, it becomes much easier to tell the difference when Egyptian Geese make sounds! Female Egyptian Geese make a loud cackling quack. Males, on the other hand, have a quieter, continuous, vibrating call. Check out the male at the rear and the female at the front of this clip to hear the difference.

#17. Tropical House Gecko

• Hemidactylus mabouia

• Length: 5 inches (12.7 cm).
• Lifespan: Between 3 and 5 years.
• Blackish-brown bands that can change color from grey to white and even dark brown.

The Tropical House Gecko is native to sub-Saharan Africa and naturally prefers scrubby and sandy areas near the beach.

However, this invasive species feels at home in suburban areas in the United States, where it is often found in homes. These geckos mainly feed on spiders, cockroaches, scorpions, moths, anoles, grasshoppers, and even other geckos.

Due to their adaptability, they are now found worldwide after being introduced by humans.

#18. Brown Anole

• Anolis sagrei

• 5 to 8.5 inches long.
• The coloring is brown, sometimes with yellow spots – this species is never green.
• The dewlap is red-orange with white borders.

Brown Anoles are a widely introduced lizard in the United States!

Look for them on tree trunks and rocks near the ground or in open grassy areas.

The Brown Anoles’ native range is Cuba, the Bahamas, and Little Cayman Island. Their population and range exploded when they were introduced in shipments of cultivated plants in the 1970s.

They established themselves so quickly that native Green Anoles had to change their behavior to survive. Because Brown Anoles eat Green Anoles and compete with them for food and territory, they’ve taken over ground habitats and pushed Green Anoles up into the trees.

#19. Greylag Goose

• Anser anser

• Greylag Geese are a soft, warm gray-brown.
• Their feathers are rimmed with narrow white edges, which gives them a delicate barred pattern over their wings, chest, and sides.
• The legs are pink, while their bills are bright orange.

Greylag Geese are NOT native to the United States!

These birds are found naturally across Europe and Asia, where they are very common and have a huge natural range.

Interestingly, Greylag Geese gave rise to almost all common domesticated goose breeds.

Domesticated Greylag Geese can commonly be seen on farms, estates, and in zoological collections. But, occasionally, escaped birds may flourish as feral populations.

Greylag Geese are very social animals. They will almost always be found in flocks, ranging from a few birds to thousands of animals. When flying, flocks adopt the classic V-shape flight formation. Play the video to see them in action!

#20. Scaly-breasted Munia

• Lonchura punctulata

• Males and females look very similar, though males have darker throats. 
• Look for brown fringes to their white chest feathers, giving them a scaled appearance. 
• They have short, triangular beaks. 

Scaly-breasted Munia are small, seed-eating birds in the finch family. They are native to the tropical regions of South and Southeast Asia. 

Their social behavior and charming vocalizations have made them popular historically as caged pet birds. The Scaly-breasted Munia was intentionally imported to the USA to be sold as an exotic pet. 

Escapees have been spotted establishing feral colonies since the 1980s but were likely present much earlier than that. Scaly-breasted Munias can now be spotted in California, Texas, Mississippi, Alabama, and Florida.

These invasive birds are very gregarious, forming large flocks of hundreds of birds. Consequently, they can cause extensive damage to crops when flocks target farms. Furthermore, Scaly-breasted Munia can outcompete native species for resources. 

• Osteopilus septentrionalis

• Large treefrogs that vary in size, between 2 and 5.5 inches long.
• Mostly gray, brown, and green colored. They can change colors to hide.
• Rough, warty skin. Inner thighs are bright yellow. Large eyes.

Cuban Treefrogs are an invasive species in the United States!

They originally came from Cuba and the Bahamas and pose quite a problem for many other types of frogs.

Credit: U.S. Geological Survey, Department of the Interior/USGS

The problem is that Cuban Treefrogs are so big! In fact, they are so large they prey upon and eat smaller frog species. Even the tadpoles can outcompete other types of tadpoles!

These nocturnal frogs adapt well to urban environments. I know I have found them on the outside of the windows of my grandparent’s home.

Here’s what they sound like!

Lastly, be careful when handling them. They secrete toxic mucus, which can cause a sharp burning if it gets into your eyes!

#23. Monk Parakeet

• Myiopsitta monachus

• Males and females look almost identical, though females tend to be a little smaller.
• Bright green plumage with blue wing tips. 
• Large orange beaks and paler chests. 

Monk Parakeets are a species of parrot originating in South America. Their ability to mimic sounds and words, combined with their social nature and beautiful plumage, has made them popular pets around the globe.

In the 1950s and 1960s, thousands of Monk Parakeets were imported as exotic pets for sale in the USA. Many of them escaped or were intentionally released over time.

These invasive birds build prolific nests in the United States.

Their nest-building has caused direct conflict with humans by damaging homes and buildings. They are gregarious birds and often build huge, chambered nests that house multiple families.

For warmth, they have taken to building these incredible nests around heating elements, such as on electrical pylons and power stations. 

This behavior has caused many issues for the people who rely on the electrical grid and the companies that maintain them. The nests can short-circuit the electrical facility, become a fire hazard, and damage equipment. Removing the nests is a very dangerous job and a temporary fix as the parakeets quickly rebuild. 

Monk Parakeets do not seem to have a strong negative impact on native fauna. They may increase competition for food and can become agricultural pests when they feed on fruit crops. However, their prolific nest-building behavior actually leads them to act as ecosystem engineers and potentially increase nesting opportunities for other bird species. They feed and nest alongside native birds with little conflict (Cristóbal Briceño et al.)

#24. Cane Toad

• Rhinella marina

• Adult length is 4-6 inches. They weigh up to 3.3 pounds.
• Coloring is light to dark brown with dark brown spots and a light line on the back.
• Large cranial crests and toxin glands make the head appear sunken in the middle.

Cane Toads are not native to the United States.

They were introduced as a pest-control species due to their huge appetite. However, the damage done by this invasive species has outweighed any benefit in controlling insect infestations.

The Cane Toad’s skin secretions are extremely toxic and can even be lethal to fully-grown dogs. In fact, they are considered dangerous to pets and native wildlife in most parts of Florida where they live.

Cane Toad Rangemap:Credit: U.S. Geological Survey, Department of the Interior/USGS

Another reason that Cane Toads are considered a dangerous invasive species is their prolific breeding habits. They have been known to reproduce in explosive numbers. For example, when they were introduced to the island of Oahu in Hawaii, their population expanded from 150 to 105,517 in just 17 months!

The call of the Cane Toad is a slow, low-pitched trill that is easily mistaken for insects like cicadas or crickets.

#25. Green Iguana

• Iguana iguana

• Males and females look very similar. Males are usually larger. 
• Green Iguanas are usually bright green but often appear orange, blueish, or gray.
• Their powerful tails make up much of their overall body length.  

Green Iguanas are large lizards native to Central America and northern South America. They are mostly herbivorous and very good at climbing trees and swimming.

They are fairly docile and have become very popular as exotic pets. However, they have sharp teeth, long claws, and powerful, whip-like tails that can cause injury. 

Green Iguana Range Map

Green Iguanas have become an established invasive species in Florida.

The primary method of introduction has been through the exotic pet trade.

In Florida, these invasive reptiles are damaging native wildlife. They feed on endangered native plants and also eat plants that are essential to the lifecycle of the endangered Miami Blue Butterfly.

Furthermore, Green Iguanas have been known to steal burrows from the Florida Burrowing Owl, which is also endangered. The burrowing behavior of Green Iguanas is also very destructive to sea walls, roads, and other infrastructure. 

#26. Brahminy Blindsnake

• Indotyphlops braminus

• Adults are small, only 5.1-10.2 cm (2-4 in) long.
• Their coloring varies; charcoal gray, light yellow-beige, silver-gray, purplish, and white are common.
• The body shape is worm-like, and they are easily mistaken for earthworms.

It is really hard to see this invasive snake in Florida.

That’s because they spend almost all their time underground in ant and termite nests and live under logs, moist leaves, and stones. Look for them in urban gardens and moist forests.

The Brahminy Blindsnake, as its name suggests, is almost completely blind. It has small, translucent eyes that can detect light but not form images. This snake species is not native to Florida. Instead, it arrived here by being transported in the soil of potted plants, which has earned them the nickname “Flowerpot Snake.”

When distressed or attacked, the Brahminy Blindsnake will try to escape underground. If touched, it might press its tail on the attacker and release a smelly musk. Despite its rather creepy appearance, this snake is completely harmless to humans.

#27. Red-eared Slider

• Trachemys scripta elegans

• Males and females appear very similar. 
• Their legs and necks are marbled with black and yellow stripes.
• They have a striking red patch behind each eye, extending to the back of the head. 

Red-eared Sliders are a species of freshwater turtle. They prefer fairly still, warm freshwater and can be found naturally around the Mississippi River and associated waterways. 

However, they spread to other areas across the continent and beyond via the exotic pet trade.  

As juveniles, Red-eared sliders are cute and very popular with pet owners and are fairly easy to care for. However, adults can grow to have shells up to 16 inches (40cm) in length. They become challenging pets that can live for up to 40 years! As a result, many Red-eared sliders were released into the wild despite this being illegal.

Red-eared Slider NATIVE Range Map

Problems These Invasive Animals Cause in the United States:

Red-eared sliders grow to large sizes and adapt well to new environments. As a result, they have been successful in competing against various native species of turtles for food, shelter, and basking sites. 

#28. Burmese Python

• Python bivittatus

• Adults are typically 10 to 16 feet long, but individuals may grow up to 23 feet!
• Coloration is tan, cream, or tannish yellow with darker brown, black-bordered blotches down the back.
• Dark head with a light stripe through each eye converging at the nose, forming a “V” pattern.

The Burmese Python is one of the largest snakes in the world!

Unfortunately, it is not native to Florida, and they are causing MASSIVE damage to ecosystems. Escaped and released snakes from the pet trade are to blame.

These invasive snakes are primarily found in the Everglades, which offer a near-perfect habitat free of any natural predators. While Burmese Pythons spend most of their time on land or in trees, they need a permanent water source to survive. They’re good swimmers and can stay submerged in the water for 30 minutes.

Burmese Pythons sit and wait for their prey, then strike their target rapidly when it approaches and use their coils to constrict and suffocate it. They feed primarily on mammals, including foxes, rabbits, and raccoons, but they also eat birds, amphibians, and reptiles. In Florida, they’ve even been observed preying on alligators and deer!

Efforts are underway to try and rid Florida of this giant predator. You may have seen the annual “Florida Python Challenge,” a competition to see who can capture the most snakes in a given time.

Here’s what to do if you see a Burmese Python:

You should report the animal via the “I’ve Got 1” hotline (888-483-4681), the EDDMapS reporting site, or an iPhone application, IveGot1.

#29. Domestic Cat

• Felis catus

• Can be a wide range of colors, sizes, shapes, and fur lengths.
• Selected mutations observed in many pet cats, such as folded ears, munchkin legs, or flattened faces, are not commonly seen among domestic cats successfully living feral.  

Sadly, domestic cats are very damaging to the ecosystems where they are introduced. It has only been in the last century or so that cats have become pets that stay indoors. 

In the United States, it is estimated that these invasive animals kill over 1 billion birds and 6 billion other small animals annually. Feral cats, who live and breed away from the care of humans, are the most prolific hunters.

As you can imagine, this issue is hotly debated due to the love people have for their pet cats. Some experts think that trap-neuter-return programs are key to curbing the problem of feral cats. At the same time, others are huge proponents of NEVER letting your cat outside.

Learn more about other animals in the United States!

• Most DANGEROUS Animals in the United States!

• MOST Common Birds in the United States

• Types of MAMMALS Found in the United States!

Which of these invasive species have you seen in the United States?

Leave a COMMENT below!

The post 29 INVASIVE Animals found in the United States! (2024) appeared first on Bird Watching HQ.

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