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Invasive Animal Species in the United States

Abhijit Naik
European starlings were introduced in the U.S. as a tribute to William Shakespeare, nutria were imported for their fur, Burmese pythons were brought in as pets, and wild boars as game species.
Such accounts of how various invasive animal species reached the United States and turned rogue, spelling trouble for the native wildlife, are quite interesting in themselves.
At the 2013 Python Challenge initiated by the Florida Fish and Wildlife Conservation Commission (FWC), the grand prize for catching the most number of pythons was $1,500. Beside this, there was a prize of $1,000 for the longest python specimen caught. That, undoubtedly, is a lot of money.
Such is the menace of Burmese pythons in Florida, that the authorities are now forced to come up with out-of-the-box ideas like this, to encourage people to participate in their war against this invasive species.
A similar event, the Lionfish Derby is held in the Florida Keys. If the Python Challenge targets the Burmese pythons that have invaded the Everglades, the Lionfish Derby targets the lionfish species that have invaded the Atlantic Ocean.
While the 68 pythons caught at the 2013 Python Challenge, or the 2,694 lionfish caught at the 2012 Lionfish Derby won't really dent the population of these species, the organizers believe that events like these will make people aware of the threat such invasive species pose to the ecosystem.
The Burmese python and lionfish are just two names featuring in the considerably lengthy list of invasive animal species that have wreaked havoc in the United States.
While some of these animals were brought as exotic pets, some were imported for their commercial uses, and there were some that hitchhiked their way into the United States aboard ships, in cargo, or using pets as carriers.

America's Most 'Unwanted' Animal Species

In the United States, invasive species are found in nearly all the states, and yet, the first state to come to ones' mind when we talk about them is likely to be Florida -- with the Everglades having an unusually large number of intruders to its credit.
Other than the Everglades, invasive species have also been making life difficult for the native species in the Great Lakes region, Hawaii, East Coast, and quite a few southwestern states.

Burmese Pythons

Other names: Python bivittatus, Python molurus bivittatus
Origin: Southeast and South Asia
Estimated population: 30,000 - 100,000
Florida seems to be the most-preferred destination for invasive species, and leading from the front is the Burmese python -- one of the largest snakes in the world. Burmese pythons were introduced in the United States when exotic pet trade was at its peak.
Many people kept these huge reptiles as pets, only to release them in the wild when they realized that it was not going to be an easy task. Their population in the wild flourished, as there were no natural predators to keep a check on their rising numbers, and very soon.
They were all over the Everglades, preying on native species like deer, Key Largo woodrat, wood storks, etc. Even though it is illegal to import Burmese pythons into the United States today, that comes across as a textbook example of the idiom, 'too little, too late.'

Feral Hogs

Other names: Sus scrofa, wild boar, feral pig, wild hog
Origin: Europe
Estimated population: 6 million
According to Dr. Brady Barr of the National Geographic Society, Burmese pythons are not as threatening for the Everglades ecosystem as the feral hogs are.
Now that can very well be a possibility because these feral hogs don't just damage the native plant species and crops, but also act as the carriers of various parasites and diseases that can adversely affect human health.
During the colonial period, early sailors introduced domesticated pigs and wild boars from Europe to the North American mainland; first, as a food source, and later, as a game species. The feral species on rampage in the US today are the descendents of domestic pigs and wild boars, that had escaped from farms and shooting reserves during that period.

Asian Carp

Other names: Bighead carp, grass carp, silver carp, etc.
Origin: Eurasia
Estimated population: Unknown
In the United States, the term Asian carp is used for any of the heavy-bodied cyprinid fish native to Eurasia. Of these, four species in particular -- the common carp, grass carp, bighead carp, and silver carp, are considered invasive.
Asian carps were introduced to the United States as a food source back in the 19th century. They are found in almost every American state today, and at the rate at which they are spreading, it won't be long before they take over various rivers and lakes in the country.
The only thing that is holding back the Asian carp's invasion of the Great Lakes is an electric barrier installed by the authorities, and that, again, is just a temporary solution.


Other names: Myocastor coypus, coypu, swamp beaver
Origin: South America
Estimated population: Unknown
A semi-aquatic rodent, harvested mainly for its fur, the nutria has become a pest in various parts of the world today. In the United States, it was introduced in the 1930s to boost fur production. As the returns from this trade weren't as high as expected, firms decided to discontinue it, and all the rodents were released in the wild.
Other invasive species, even the nutria didn't have predators in their new-found habitat. This, along with their ability to reproduce rapidly, helped them spread to other regions, damaging vegetation and destroying wetlands wherever they went. As of now, the authorities have spent millions of dollars trying to eradicate these rodents, without much success.


Other names: Pterois volitans, Pterois miles, zebrafish, scorpion volitans, etc.
Origin: Western Pacific Ocean and Indian Ocean
Estimated population: Unknown
If we can't beat them, let's eat them! The National Oceanic and Atmospheric Administration (NOAA) had to go to the extent of encouraging people to incorporate lionfish in their diet as a part of its ambitious plan to take on the species, which was creating havoc in the Atlantic Ocean.
The species was brought to the United States as an aquarium fish in Florida, from where it was accidentally released in the wild when hurricane Andrew hit the East Coast.
With no natural predators in this region, and their ability to reproduce year round, the lionfish quickly spread along the Eastern Coast, Gulf of Mexico, and the northern coast of South America, preying on various native species of the Atlantic.

Africanized Honey Bee

Other names: Africanized bees, killer bees
Origin: Europe and Africa
Estimated population: Unknown
Africanized honey bees, or the killer bees that they are widely known as, are hybrid species of the African bees. It was hybridized by crossbreeding African bees with European bees in South America. The presence of Africanized bees in the United States was first recorded in the 1990s, from Texas.
Since then, they have spread to many other states in southwestern United States. Though they were hybridized with the sole intention of boosting honey production, it didn't quite go as planned.
The overly aggressive Africanized species started attacking the European honey bees and taking over their hives, thus, doing more harm than good to the honey production sector.

European Starling

Other names: Sturnus vulgaris, common starling, English starling
Origin: Europe
Estimated population: 200 million+
The European starling was introduced in the United States in 1890 by the American Acclimatization Society as a part of their grand plan of bringing every bird mentioned in William Shakespeare's work to the North American mainland. Little did they know what was in store for them.
The species adapted to its new habitat and started expanding its range at an alarming rate, spanning the entire United States by the 1940s. It destroyed standing crops, competed with the native species, eventually displacing them, and even served as a biological vector for the E. coli species of bacteria.

Asian Tiger Mosquito

Other names: Aedes albopictus
Origin: Asia
Estimated population: Unknown
In the Global Invasive Species Database, the Asian tiger mosquito has been enlisted as one of the 100 most invasive species in the world. It was introduced in continental United States in 1985, when a shipment of used tires from Japan landed at the port of Houston.
Within the next 2 years, it had spread to as many as 17 states across the country. The data compiled by the Centers for Disease Control and Prevention (CDC) shows that it is found in at least 26 states today. Asian tiger mosquitoes are responsible for the spread of dengue disease in states like Florida, Texas, Georgia, Maryland, and Hawaii.

Brown Marmorated Stink Bugs

Other names: Halyomorpha halys
Origin: Eastern Asia (Japan, Korea, and China)
Estimated population: Unknown
It is difficult to say when the brown marmorated stink bug was introduced in the United States, but the first instance of the species being recorded in the country came in 1998 from Pennsylvania. A known agricultural pest in its native habitat, the species wreaked havoc in the United States.
At its peak in 2010, stink bug infestation cost the apple farmers of the Mid-Atlantic region $37 million in loss. As of 2011, the species has been recorded in as many as 36 states across America.

Gypsy Moths

Other names: Lymantria dispar
Origin: Europe
Estimated population: Unknown
In 1869, Étienne Léopold Trouvelot, an artist with keen interest in entomology, decided to import gypsy moths from Europe and use them to boost silk production. While Trouvelot was carrying out his plan, some of these moths escaped in the wild. Exactly 20 years later, the first gypsy moth outbreak was recorded in the United States.
Over the course of time, the species has spread all over Eastern United States, destroying a large number of hardwood trees. The rapid spread of this species is also aided by the fact that its larvae is carried by wind from one place to another.

Exotic or Invasive

An exotic species is one which is not native to the said region, but instead, has been deliberately or accidentally introduced there. These species are also known as introduced, non-native, or alien species. An invasive species, on the other hand, are exotic or introduced species which threaten the ecology of the said region. Also referred to as invasive exotics, these species acclimatize to the new conditions and start multiplying.
The ability to adapt to a new environment happens to be one of the key attributes of invasive species. These species spread very fast, compete with the native species for food, displace or even wipe off the native species at times, and even serve as the carriers of human diseases. So, they are not just a threat for the ecology and economy, but are also a threat for our health.
Of the 50,000 odd non-native species of plants and animals found in North America today, only around 4,500 are considered invasive, and yet, the amount of money spent in damage repair and control of these species goes well into the billions.
It is difficult to say 'exactly' how a species will react when it is introduced into a new ecosystem, but based on its characteristic traits, one can get a rough idea of the same.
A species which is highly adaptable, has a long lifespan, reproduces round the year, and has no natural predators in the new habitat, is more likely to turn rogue over the course of time. As in case of the brown marmorated stink bugs, even the abundance of a particular species in its native habitat can give a hint about its future in the new habitat.
If you happen to notice any invasive exotics in your neighborhood -- plant or animal -- you can either try to eradicate them on your own, or contact the authorities for help; ideally the U.S. Fish and Wildlife Service (FWS), or the U.S. Geological Survey (USGS). You do have the option of leaving it alone, but that's one thing we will never recommend... because of some obvious reasons.