Weird Nature The Most Damaging Invasive Species in the World  

analise.dubner
573 votes 66 voters 2.5k views 102 items

List Rules Vote up the things that you believe are the most damaging invasives through direct or indirect experience.

Ecosystems on our planet are, as we have learned over and over as a species that seems to live outside them, much more fragile than we've given them credit for. Sometimes it only takes the introduction of one species to upend the whole boat. This can happen naturally... say a flood or a windstorm blows an invader into a new biome that is not prepared for it... but it is usually humans that are responsible for bringing these invaders in. Sometimes it is by accident, and other times we do it to solve a problem that we, ourselves, have created; then going on to make it so much worse. Insects and viruses can be carried across oceans by boats, on livestock or even our clothing. Animals can be imported as pets and then let loose... or imported as a possible resource, and then found to be deeply destructive and impossible to control. Island ecosystems are deeply vulnerable, often having completely endemic, carefully balanced food chains and interspecies relationships. The introduction of a single new animal can, and has, completely upended that balance. Large-scale agriculture is also vulnerable to a single invader that it has no defense against. We can struggle to right these human-caused wrongs, but often find ourselves helpless in the face of an imbalance we have no way to fight. This is a list of the most destructive invasive plants, animals and diseases on Earth. Vote up the ones that you have experienced the impacts of, either directly or indirectly.

list ordered by

1
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Carp is listed (or ranked) 1 on the list The Most Damaging Invasive Species in the World

Origin: Europe and Asia

Originally from Europe and Asia, the common carp has been cultured far and wide as a valuable food source for over 2,500 years. It is the third most introduced species in the world. They are an aggressive, omnivorous fish known for consuming resources to the point of depletion. This carp is one of the most damaging aquatic invasive species due to its wide distribution and severe impacts in shallow lakes and wetlands. On top of the fact that they outcompete native fish, their feeding also disrupts shallowly rooted plants muddying the water. They release phosphorus that increases algae abundance and they cause a decline in water quality that then causes declines of aquatic plants needed by waterfowl and fish. In the US, many people do not consider this fish to be an invasive because it has been around for so long and they also enjoy it as a sporting fish. In some countries, however, control methods are employed that include barriers, harvesting, traps and water level manipulation as well as electric barriers, bubble curtains and sonic barriers.

2
18 5
Kudzu is listed (or ranked) 2 on the list The Most Damaging Invasive Species in the World
Kudzu

Origin: Japan

Going by several not-so-flattering nicknames, Kudzu is well known to areas that is is not native to. It's hard to miss, as it covers everything. The Kudzu vine is native to Japan, but arrived in the US in 1876 when it was featured at an expo as a hardy, fast growing vine that could fight soil erosion. Well. They weren't wrong about that part. Also known as the 'mile a minute' vine and the 'the vine that ate the south', Kudzu has been spreading across the country at 150,000 acres a year. In the right conditions, a length of vine can grow a foot in a single DAY. The vines themselves grow up to 100ft long and the plant can smother trees, houses, power lines and whatever else that can't move out of the way. It is drought and frost tolerant and practically unstoppable. Nothing can compete with it, and thus, it wins. This invasive easily sits in the top 10 of the worst case scenarios that happen when an organism has no natural barriers built into its ecosystem.

3
11 1
Red Lionfish is listed (or ranked) 3 on the list The Most Damaging Invasive Species in the World

Origin: South Pacific

Most would agree that the lionfish is one of the most beautiful fish in the sea. It seems as if it were designed as jewelry. However, looks aside, it is an exceedingly destructive invasive species. It first appeared in coastal Florida waters around the 80s, probably the result of exotic animal stocking of aquariums. Once free in its new, fresh ecosystem it began preying on many important commercial fish. Lionfish now inhabit reefs, wrecks, and other habitat types in the warm marine waters of the greater Atlantic. Adults are primarily fish-eaters and have very few predators outside of their home range.  They eat the herbivores that eat algae from coral reefs. Without these herbivores, algal growth goes unchecked, which can be detrimental to the health of coral reefs.

4
14 2
Red imported fire ant is listed (or ranked) 4 on the list The Most Damaging Invasive Species in the World
Red imported fire ant

Origin: Brazil and Argentina

Originating in Argentina and Brazil, there are few that have never heard of the fire ant, one of the worst invasives in the world. In the US, it is thought that the first ant arrived in Mobile, Alabama via cargo ship somewhere between 1933 and 1945. In Australia it is believed to be closer to 2011. It has since caused billions of dollars in damage to the areas it now infests. The ants thrive in urban areas, so their presence may deter outdoor activities, but more damagingly, nests can be built under structures such as pavements and foundations, which may cause structural problems, or cause them to collapse. They also can damage equipment and infrastructure and impact business, land, and property values. As the workers are attracted to electricity, they can swarm electrical equipment and destroy it. In agriculture, they can damage crops, damage machinery, and threaten pastures. They are known to invade a wide variety of crops, and mounds built on farmland may prevent harvesting. They also pose a threat to animals and livestock, capable of inflicting serious injury or killing them, especially weak or sick animals. So far, the only ways of controlling these ants has been found to be baiting and pesticides. Due to its capability for damage, the ant has become one of the most studied insects on earth.

5
16 4
Feral Pig is listed (or ranked) 5 on the list The Most Damaging Invasive Species in the World
Feral Pig

Origin: Eurasia

Considered one of the most outright destructive invasive species of all time, these pigs were originally brought to the US for domestication from Europe and Asia. Some escaped captivity and took to the new environment easily. Prolific breeders, they can produce four to eight babies per litter. Feral swine are highly adaptable, but prefer habitats with an abundant supply of water and dense cover. They are aggressive and pose serious ecological, economic, and health threats. They are extremely destructive to fields, fences, and facilities. Their wallows can affect ponds and wetlands, muddying the water and destroying aquatic vegetation. They can strip a field of crops in one night and pose a threat to ground-nesting birds and some endangered species. To make it even worse, they can transmit diseases and parasites, such as pseudorabies, brucellosis, and tuberculosis, to livestock and people. It is estimated that they do at least 1.5 billion dollars worth of damage a year - conservatively. A quarter of that alone is in Texas.

6
14 3
Asian tiger mosquito is listed (or ranked) 6 on the list The Most Damaging Invasive Species in the World
Asian tiger mosquito

Origin: Northern Asia

This small, striped day-biter has been in the news in recent years in California, having newly arrived to join the phalanx of ultra-annoying mosquito species that already live there. Previous to California, it was first found in the US in 1985 in Texas. Since that time they have been spreading rapidly and unabated across the country. They prefer warm weather, so they have been identified in every county in Georgia, Florida, South Carolina and Tennessee, as well as many counties in surrounding states. They breed in small puddles of standing water near human habitation, in diverse places, varying from cemetery vases to junk piles. Like other invasive species, the Asian tiger has out-competed native mosquitoes, such as Aedes aegypti, the yellow fever mosquito, but that's not necessarily good. The tiger mosquito can spread diseases too, such as West Nile, dengue fever or Eastern equine encephalitis. In fact, its habit of staying close to where people live and biting multiple hosts in the daytime, make it an even more efficient vector for some diseases. Stay safe by following standard anti-mosquito protocols; including removing any standing water source from near your house if possible, no matter how small.

7
6 0
Nutria is listed (or ranked) 7 on the list The Most Damaging Invasive Species in the World
Nutria

Origin: South America

Brought in from South America, the nutria was originally meant to start a fur industry. Due to releases and escapes, there are now large wild populations in North America, Europe and Asia. They wreak havoc in US wetlands. The burrows and tunnels nutria construct often damage levees that prevent rivers from overflowing as well as man-made canals and ditches. As a result, streambanks erode or become unstable. The species also feasts on the roots of the plants that comprise marsh habitats, which are home to ducks, geese, and muskrats. They can convert grassy marsh into unproductive open water by attacking the very structure that holds the marsh together, the vegetative root mat. Once these giant rodents chew through a mat and expose mud, tidal currents and wave action lead to erosion. The pitted marsh surface sinks and vegetation is lost to flooding. Areas destroyed by nutria become permanent, open water ponds called “eat outs.” Finally, and perhaps most destructive to the economy, is the Nutria's appetite for rice, corn, and sugarcane. Many control attempts have been made including trapping, baiting, poisoning, fencing, controlling vegetation, draining and grading  potential home sites. Eradication is the only answer to save the marshes from these terribly destructive invasive animals.

8
6 0
Brown tree snake is listed (or ranked) 8 on the list The Most Damaging Invasive Species in the World
Brown tree snake

Origin: Australia

Considered one of the most famous case studies of an invasive species, the Brown Tree snake was originally from Australia but now terrorizes the islands of the South Pacific. On the island of Guam, the snake is responsible for the decimation of the bird population. Birds had no reason to fear an animal that they had never before dealt with until it suddenly appeared, arriving by accident in the 50s. Although some sources speculate that it was deliberately introduced to control rats and mice, it is more likely that the original invaders were stowaways aboard military aircraft and cargo ships from the Solomon Islands. Over the next several decades, the brown tree snake eliminated both of the island’s two endemic bird species, two of the three native bat species, and several species of seabirds that used the island for breeding. Some of those species had served as critical pollinators for many of the island’s plants, and their decline brought about a decline in the number of plant species on the island. A 2017 study also showed that the snake’s elimination of many fruit-eating birds resulted in cascading reductions in seed dispersal, which led, in turn, to dramatic declines in population of two of the island’s important fruit trees. Hawaii remains on high alert against this menace.

9
12 2
Brown marmorated stink bug is listed (or ranked) 9 on the list The Most Damaging Invasive Species in the World
Brown Marmorated Stink Bug

Origin: China

This damaging and hard-to-eradicate insect is believed to have first arrived in the US in packing crates or on machinery shipped from China. The first documented specimen was collected in Allentown, Pennsylvania, in September, 1998.  Not only does it smell bad - hence the name - but it has the ability to eat its way through a variety of crops, from cotton to apple. It has an uncanny and unfortunate ability to avoid pesticides. Once introduced to an area, this pest can take years to build up enough population to destroy an entire crop... somewhere between 8 and 10 years depending on the local climate and situation. Once established, however, the numbers can explode and new populations can spread, partly because the climate of the US is paradise for the stink bug. In fact, there does not appear to be any environmental limiting factors that are slowing their spread across the United States. They also are extremely mobile insects capable of moving from host to host without causing disruption in their reproductive processes. Currently it is estimated that BMSB populations will continue to grow and spread to other states, especially during unusual periods of warm weather.

10
13 3
Burmese Python is listed (or ranked) 10 on the list The Most Damaging Invasive Species in the World

Origin: Southeast Asia

This invasive story sounds like science fiction. Burmese Pythons are not animals you think of when you think of Disneyworld and caftan-dressed grandmas on the beach... but they have become a top predator in Florida. Living off bountiful native populations of deer, raccoon, marsh rabbits, bobcats and possum, these stealthy hunters have declined those populations by up to 99 percent in some cases. That is staggering. Pythons take to Florida's climate like a snake to a swamp, and because they have no natural predators there other than humans and alligators, they are happily increasing their numbers. They are creating this problem because they are a popular pet, and many people who like snakes for pets get them. Once they get too big (a thing that Pythons DO), they get dumped in the swamp by their idiot ex-owners. It is estimated that 99,000 Burmese Pythons were imported to the US between 96 and 2000. If even only half their owner dumped them, that's a lot of pythons. Ironically, they are considered a 'threatened' species in their homeland. Currently, these snakes continue to make Florida their home despite efforts to control their population. They are stealthy and very hard to find and kill, thus, they will only continue to wreak havoc on Florida's ecosystem.

11
10 1
Tilapia Fish is listed (or ranked) 11 on the list The Most Damaging Invasive Species in the World

Origin: North, West Africa & Middle East

The Tilapia fish found its invasive status when it was intentionally and unintentionally released in waters that were not its native African coastlines. It has been introduced as food for predatory fish, as a human food source and as a means of aquatic plant control; however like so many of these stories the impact was not taken into consideration when it was released. Now, tilapia has been implicated in mussel population decline in Texas. It is a competitor with native species for food, spawning and space. In some places where tilapia now thrive the streams have lost most vegetation and nearly all native fish.

12
11 2
Zebra Mussel is listed (or ranked) 12 on the list The Most Damaging Invasive Species in the World
Zebra Mussel

Origin: E. Europe and W. Russia

Another ballast water hitch-hiker, the fingernail sized Zebra mussel arrived from Europe in 1988 and established a colony in the great lake region. They soon spread their way through the lakes, down the Mississippi and throughout the eastern US. Ravenous filter feeders, they rapidly deplete the water of food, out-competing the native organisms. They cluster by the millions, clinging to every solid surface. They create a costly problem for power plants, cities and residents when they clog water intakes. They kill native mussels and they slice open the unsuspecting feet of any swimmer or pet that steps on them. There has yet to be found an efficient way to control them, but researchers have tried special paint that keeps them from adhering to docks and pipes. There has been some experimentation with ion emitters that the mussels seem not to like, but for the most part nothing has worked yet.

13
12 3
Feral Cat is listed (or ranked) 13 on the list The Most Damaging Invasive Species in the World
Feral Cat

Worldwide

While the house cat may seem like a strange addition to this list, consider: being a domesticated animal, it is not a native species to any of the habitats it currently impacts. It is listed here as a feral cat, but even your cuddly home companion has an astounding impact on the ecosystem you live in. The domesticated cat is a major threat to native amphibians, reptiles, birds and small mammals, many of which are endangered. In New Zealand alone it is considered to be responsible for the decline of 76 bird species. In Australia it has caused the extinction of some species on islands and is thought to have contributed to the disappearance of many ground-dwelling birds and mammals on the mainland. When introduced to small, fragile island ecosystems, the impact is even higher;  causing  or contributing to 33 (14%) of the modern bird, mammal and reptile extinctions recorded by the International Union for Conservation of Nature (IUCN) Red List. Today, more than 100 million feral and outdoor cats function as an invasive species with enormous impacts - even well-fed cats will hunt and kill. Domestic cats are easily one of the worst, most-damaging invasive species in the world.

14
14 5
Emerald Ash Borer is listed (or ranked) 14 on the list The Most Damaging Invasive Species in the World
Emerald Ash Borer

Origin: Asia

The emerald ash borer is a menace that, while sparkly, creates devastation the ash trees left in its wake. The adults do little damage for the most part, however, once they bore nickel sized holes, they deposit their larval offspring behind to carve wiggly, damaging tunnels through the bark and disrupting the tree's ability to transport water and nutrients. It is thought to have arrived in the US in wood packing material carried on cargo ships from Asia around 2002. As of May 2018, it is now found in 33 states, and the Canadian provinces of Ontario, Quebec, and Manitoba. Ash trees lose most of their canopy within 2 years of infestation and die within 3-4 years. If you find it, please report it to your local authorities. The only ways to control this beetle are with pesticides, removing the tree, or the experimental biocontrol method of the parasitoid braconid wasp, which will lay its eggs in the beetle and kill it.

15
8 1
Mediterranean Fruit Fly is listed (or ranked) 15 on the list The Most Damaging Invasive Species in the World
Mediterranean Fruit Fly

Origin: Sub-Saharan Africa

In 1929, the first infestation of the Mediterranean Fruit Fly - or Medfly - in the US were recorded in Florida. Since that time, this pest has continued to attack more than 260 different fruits, vegetables and nuts. These flies lay their eggs in the fruit and the larvae then feed off the flesh of the crop. Even worse, the tunnels that the larvae make leave the fruit or vegetable vulnerable to bacteria and fungi which cause it to rot. And, to add insult to injury, the maggots then attack the roots, stems and buds of the plant. They can be painstakingly eradicated by keeping a close eye for even a single fly and, once ID is positive, increasing the number of traps and pesticide. Any infected soil has to be treated and all fruit stripped from any known host trees, bagged and removed to a landfill. There has also been some success with the release of sterile flies that will eventually neutralize the population.

16
8 1
Asian Citrus Psyllid is listed (or ranked) 16 on the list The Most Damaging Invasive Species in the World
Asian Citrus Psyllid

Origin: SE Asia

This is a bad one. First detected in 1998 coming in from imported plants from Asia, this little insect survives by feeding on the sap of citrus leaves. As it eats, it injects its toxic saliva into the plant... a saliva that often carries Huanglongbing or HLB disease, which infects the tree and causes the citrus fruits to be discolored. The poor tree then goes on to die in 3-5 years, reducing orange production. This disease has already forced the Florida citrus market to grow indoors and went from over 80 citrus companies in Florida alone to only 35 firms; leaving trees, people and their livelihoods devastated by this bacterium. It reached California in 2008 and has resulted in quarantines and restrictions. A year later, it was found in Georgia, South Carolina and Louisiana. 2012, it arrived in Texas.  While some research has found some footing in the war against Citrus Greening disease, it remains a real and terrible threat to the entire Orange growing industry.

17
9 2
Formosan Termite is listed (or ranked) 17 on the list The Most Damaging Invasive Species in the World
Formosan Termite

Origin: Taiwan

Originating from Taiwan or perhaps China before that, the first Formosan Termite probably arrived in the US via ship. It was first reported in a Houston shipyard in 1965 and has since spread across the southern US. Sometimes called the super termite, this little bastard is one of the most destructive insects in the US. This particular species can tear through wood like a buzzsaw - faster than any other species.It is known to consume over 50 living plant species as well as structural lumber, plastics, asphalt and even thin metals. Not only is it an aggressive eater, but it is also territorial. They are very expensive pests to deal with. In Hawaii for example, annual costs to control them exceed $100 million dollars and in Florida, $60 million. Physical barriers such as special sand or wire mesh installed under buildings at the time of construction are used where Formosan subterranean termites are troublesome, but such barriers are very expensive. Expensive or not, a sobering statistic: once established, Formosan subterranean termite has never been eradicated from an area.

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10 3
Black Rat is listed (or ranked) 18 on the list The Most Damaging Invasive Species in the World
Black Rat

Origin: SE Asia

Originally from tropical Asia a long, long time ago, the black rat is most likely one of the first invasive species to ever be inadvertently distributed by humans. It is thought to have reached Europe by the first century A.D. before spreading across the globe on European ships. Since then, the black rat has thrived in just about every region of the world, and has adapted with ease to rural, urban, and suburban environments alike. Unfortunately, its success as a species alongside other rat species, has caused dramatic population declines and even extinction of countless bird, reptile, and other small vertebrate species all around the world.

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8 2
European Starling is listed (or ranked) 19 on the list The Most Damaging Invasive Species in the World
European Starling

Origin: Europe

One of the worst nuisance birds in America, the European Starling is no native. It was brought to the Americas in 1890 by a NY drug manufacturer named Eugene Schieffelin. He had a simple-minded thought to introduce birds mentioned in Shakespeare to the country. What could go wrong? The starling has now had a good amount of time here and now numbers 750 million to 1 billion (according to the USDA) and is found everywhere across the country. And these birds are obnoxious, traveling in huge flocks of over 1,000 birds. Not only do they pose a huge threat to agricultural crops by descending like a horde of locusts and devouring everything, but they also even pull up seedlings by the root. Starlings cause over $1 billion of annual damage to the agricultural industry alone. Their birdshit is vectors for several infectious diseases and to top if off, they are a hazard to air travel, having brought down jetliners. They are well-established and seem to be going nowhere now... despite many attempts to manage their populations with poison, shooting and even trained falcons. How's that Shakespeare, Eugene?

20
8 2
Spotted Lanternfly is listed (or ranked) 20 on the list The Most Damaging Invasive Species in the World
Spotted Lanternfly

Origin: Asia

The Spotted Lanternfly is a bright, red and black moth-like insect and one of the more devastating and hard to control US invaders in recent history. It eats almost everything, making it even worse than the Emerald Ash Borer. One of the things that makes it so damaging is that it is not very tasty to anything that lives in America, thus it eats and eats unabated. Since first being discovered in 2014, it has made its way across 13 counties in Pennsylvania munching on crops and trees of all kinds. There is a nationwide watch for it, and if you see it, please report it to your state or local officials.  

21
9 3
Chestnut blight is listed (or ranked) 21 on the list The Most Damaging Invasive Species in the World
Chestnut Blight

Origin: Asia

One of the few fungi on this list, Chestnut Blight first came to the US fro Asia in the 1900s carried in on infected plants. The disease is transferred in a variety of methods such as air, wind, and animals. Hosts become infected by open vulnerable wounds that are moist, creating an ideal environment for chestnut blight. Once established the fungus forms yellow-orange fruiting found on the older areas of the cankers on the host tree. The American Chestnut tree, unable to develop adequate defenses, has been found to be particularly susceptible to this fungus. As a result, large forested areas have been devastated by infection from chestnut blight resulting in the loss of trees in large quantities. Sadly there is no effective method of treating chestnut blight. Once a tree contracts the disease (as they all eventually do), there is nothing to do but watch it decline and die. The prognosis is so bleak that when experts are asked how to prevent chestnut blight, their only advice is to avoid planting chestnut trees altogether. The tree has been declared all but extinct, however there are still efforts to save the species. The Chinese Chestnut is immune and attempts to cross pollinate with the American tree by hand is underway. It could be many decades before we know if the transgenic species will be successful.

22
9 3
Africanized bee is listed (or ranked) 22 on the list The Most Damaging Invasive Species in the World
Africanized Honey Bee

Origin: African/European Hybrid

The Africanized honey bee is a slightly unusual case, a bit of a Frankenstein's monster. It's a species cross-breed between aggressive Tanzanian bees and docile European honey bees. This was done as a way to try and increase honey production, however, the result was a very angry honey bee. That would have been the end of the story, but unfortunately in 1957, a beekeeper in charge of the hybrids accidentally released 26 Tanzanian queens in Sao Paolo, Brazil. These queens went out, found some european honeybees and multiplied. These hybrids are aggressive and hyper-territorial. They out-compete any native bees in the region they occupy. Africanized honeybee swarms have been known to invade regular honey bee hives, kill the European honey bee queen and install their own leader. They are less likely to store honey like the domesticated bees and they are quick to abandon a hive. The bees first infiltrated the U.S. in 1990 and have since spread to the southern parts of many states, including California, Nevada, Utah, Arizona, New Mexico, Texas, Oklahoma, Louisiana, Arkansas and Florida. Despite what fun TV movies of the week might make you think, their sting is no more toxic than any normal honey bee, however, because of their intense aggression, they have been known to swarm easily and sting many times, making them a threat to humans as well as honey production. 

23
6 1
New Guinea Flatworm is listed (or ranked) 23 on the list The Most Damaging Invasive Species in the World
New Guinea Flatworm

Origin: New Guinea

Native to New Guinea, this flatworm was accidentally introduced to the soil of many countries. It was also deliberately introduced into two Pacific islands in an attempt to control an invasion of the Giant East African Snail. It has since grown to have a detrimental impact on biodiversity has earned a spot on the '100 worst invasive alien species' list. This worm is spread by humans, reproducing quickly. When it comes into a new habitat it will quickly adapt and eat any snail or invertebrate it can find. The flatworm has had multiple impacts on the ecosystems it has been introduced to. In the Pacific Islands, several native land snails have either gone extinct or their numbers have drastically reduced. It is such an efficient and invasive species that it has caused the decline and extinction of gastropods on several islands and consumes more endemic land species than other species. It even outcompetes other predatory flatworm species. Currently, there are no known methods for controlling the population of P. manokwari. This makes the eradication of the invasive species especially difficult.

24
5 0
Asian Gypsy Moth is listed (or ranked) 24 on the list The Most Damaging Invasive Species in the World
Asian Gypsy Moth

Origin: Eurasia

Now one of North America's most devastating pests, the Gypsy Moth originally lived in Europe and Asia. In the late 1860s it is thought to have arrived in Boston and has wreaked havoc on North American forests since. Due to its unending appetite and ability to multiply quickly, this moth causes incredible damage to forests, nurseries, vegetation along creeks and rivers, and trees and shrubs in yards and parks. Because of the defoliation, it alters wildlife habitat and affects the quality of life in communities that experience repeated outbreaks. The USDA estimates that the economic cost of gypsymoths has averaged $30 million a year for the past 20 years. Gypsy moth controls include cultural, mechanical, and chemical controls; natural predators; and silvicultural practices. Unfortunately, because it's a nonnative pest, gypsy moth has few natural controls and none capable of preventing its eventual establishment.

25
5 0
Northern snakehead is listed (or ranked) 25 on the list The Most Damaging Invasive Species in the World
Northern snakehead

Origin: Asia and Africa

Looking like a mutant crossbreed between a python and an eel, the aptly named Snakehead competes with native species for food and habitat. No one really knows how it got into the US waterways, but it is now the most feared fish in Chesapeake Bay watershed. During all life stages, snakeheads compete with native species for food and habitat. When young, they eat zooplankton, insect larvae, small crustaceans, and the young of other fishes. As adults, they become voracious predators, feeding on other fishes, crustaceans, frogs, small reptiles, and sometimes birds and small mammals. Beyond their ability to wreak havoc on ecosystems, there is also concern for the snakehead’s potential to transfer pathogens to native fishes, because snakeheads can carry diseases and parasites that have the potential to be harmful. Snakeheads are now on the list of injurious wildlife under the Lacey Act.

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6 1
Dutch Elm Disease is listed (or ranked) 26 on the list The Most Damaging Invasive Species in the World
Dutch Elm Disease

Origin: Western Himalaya

Accidentally brought to the US in 1930 via imported, infected logs from the Himalayas it wasted no time spreading among trees that had no natural resistance to the non-native invader. The first case of the fungus destroying American elms was immediate. Two years later it had spread across the east coast, wiping out trees in New Jersey. By 1970 it had destroyed 77 million trees. It spreads by bark beetles that feed on the trees -- it then impacts the ability of the tree to spread water and nutrients throughout itself and one by one the branches die, finally killing the tree. No American elm has yet to develop resistance to this devastating fungus. Dutch elm disease is widely recognized as the largest threat to elm trees in the United States.

27
7 2
Water hyacinth is listed (or ranked) 27 on the list The Most Damaging Invasive Species in the World
Water hyacinth

Origin: South America

Considered one of the worst aquatic weeds in the world, the water hyacinth's beautiful, large purple and violet flowers belie its invasive and damaging nature. Now found in more than 50 countries, it is a fast growing plant that can double its population in as little as 12 days. It blocks waterways, limits boat traffic and recreation. It also prevents sunlight from penetrating the water surface which kills the plants that grow on the bottom. It clogs canals, rivers and lakes; displaces native plants and animals; and interferes with the irrigation of many crops, navigation, fishing and the activity of electric power stations. It can be controlled physically by raking it off the surface, biologically with the neochetina beetle and with a variety of herbicides.

28
6 1
Cane Toad is listed (or ranked) 28 on the list The Most Damaging Invasive Species in the World

Origin: Central and South America

Classified as an invasive species in over 20 countries now, the Cane Toad has only people to blame. Because it is a predator of many pests that affect agriculture, it has been deliberately released in regions it is not native to many times over. Almost every time it has managed to out-compete the natives and its populations have become a threat to the areas it's been introduced to. There are many reports of it moving into a new area only to be followed by a decline in the biodiversity in that area. The most documented invasion and subsequent effect on native species is Australia, where multiple surveys and observations of the toad's conquest have been completed.

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Field Mouse is listed (or ranked) 29 on the list The Most Damaging Invasive Species in the World
Field Mouse

Origin: India and SE Asia

Having a relationship with humans that goes back at least 8,000 years, the common field mouse has remained a continuing pest and a damaging invasive. An adaptable mammal, it is implicated in the extinction of indigenous species in ecosystems they have invaded and colonized. Thought to have originally come out of India and Asia like the rat, this rodent probably has a larger worldwide distribution than any other mammal besides humans. Anyone who has ever had mice in their walls knows well how hard they can be to eradicate.

30
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Rosy Wolf Snail is listed (or ranked) 30 on the list The Most Damaging Invasive Species in the World
Rosy Wolf Snail

Origin: Southern US

In another case of bringing an invasive in to control another, previously introduced, invasive: meet the rosy wolf snail. It was introduced to India and Pacific Ocean islands in the 50s to try and control the (invasive) giant African land snail. The wolf snail is cannibalistic and will eat other snails and slugs, so it was thought it would eat the giant African. Unfortunately, it found the native snails much more delcious. Due to its voracious appetite the rosy wolf snail is a fierce invasive gastropod that can severely threaten natives. For Hawaii it is thought that the rosy wolfsnail is responsible for causing the extinction of 1/3 of the native gastropods. The Partulid tree snail, in fact has been lost and today almost all the survivors exist only in zoos. “Exclosures” have been built in Hawaii and French Polynesia to prevent the wolf snail from attacking native tree snails. These barriers are somewhat successful but require constant monitoring and maintenance. 

31
8 4
Rabbit is listed (or ranked) 31 on the list The Most Damaging Invasive Species in the World

Origin: Southern Europe and Northern Africa

One of the most famous invasive stories can be found with the cute, fluffy bunny. In 1859, the story goes, an English farmer named Thomas Austin introduced 24 grey rabbits to his farm in Australia to remind him of home and maybe provide a little hunting. Within ten short years, the rabbits had bred with local rabbits to such scale that two million could be killed of and it would have no impact on the overall population. Past that first decade, by the time the century turned over, there were so many rabbits they were contributing to soil erosion and species loss. They built a 'rabbit-proof fence' in 1907 to try and contain them, to no avail. They tried to release a virus to kill them, and while that killed a few, the survivors became immune and quickly recouped their losses. Australia has since tried several other types of bio-warfare, including creating a terrifying strain of calcivirus and warning those with pet rabbits to get them vaccinated against it. Meanwhile, ironically, rabbits are so scarce in Southern Europe that the predators that rely on them are dying off. 

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Giant African Land Snail is listed (or ranked) 32 on the list The Most Damaging Invasive Species in the World
Giant African Land Snail

Origin: East Africa

This animal's story starts the way that so many of these invasive tales begin... with exotic pet importing. In 1966 three giant African snails were illegally brought to Miami as pets. They were then released into the garden with no thought towards the potential consequences of introducing a non-native species to a new environment. Within 7 years, those three snails numbered among 18,000 and had already cost the state of Florida over a million dollars in eradication efforts - which succeeded. Unfortunately, people reintroduced them in 2011 because people are just terrible. Naturally, they have spread and the snails have been found in Ohio, Wisconsin and Illinois where there were again sold as pets. They eat plants ravenously, damaging at least 500 different types of plants and competing with native animals and insects. They will also eat stucco, wood, and plaster, causing thousands of dollars in damage. These giant pests are highly capable of becoming agricultural threats due to their large size and foraging behavior. As large and aggressive mollusks, giant African snails pose the largest threat to damaging food crops grown all over the United States. Snails from this family are known carriers of the parasite (Angiostrongylus cantonensis) which transmits eosinophilic meningitis. As yet the transmission of the disease to humans is low, but still possible. If you see this snail, please alert local authorities, don't make it your pet.

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Red-eared slider is listed (or ranked) 33 on the list The Most Damaging Invasive Species in the World

Origin: Mississippi River

Red-eared sliders come with all the abilities needed to be effective invaders. They reach sexual maturity at a young age and reproduce quickly and successfully. They compete with native turtle species for food, habitat, and other resources. These turtles can get pretty big and have the fun quality of being aggressive; bullying native turtles out of basking sites, a critical resource for these reptiles. Reduced access to these sites can slow growth and increase mortality of native turtles. Additionally, red-eared sliders raised in captivity can develop diseases that are unfamiliar to wild turtles. Upon release, these reptilian 'typhoid marys' can introduce diseases that can seriously harm native populations. Can people stop with exotic pets they grow tired of and dump outside, please?

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BD Fungus (Chytrid) is listed (or ranked) 34 on the list The Most Damaging Invasive Species in the World
BD Fungus (Chytrid)

Origin: East Asia

This fungus is a type of chytrid, one of over a thousand different species that live only in water or wet environments. They are some of the oldest and most primitive types of fungi on Earth. Some feed on dead organic matter and others feed on living things. In the 80s, scientists took note of a global decline in amphibian populations. Then, in 1999 a new species on chytrid was discovered that infected the skin of amphibians and kills them. Since that time, some frog species have gone extinct in the wild and of the 1,400 (of 7,800) species tested for the fungus about half showed signs of it. More research dollars are being asked for and attempts to tamp down on shipping amphibians for the exotic pet industry have occurred. In the meantime, initial research has shown that some frogs might be developing resistance on their own.

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Gray Squirrel is listed (or ranked) 35 on the list The Most Damaging Invasive Species in the World
Gray Squirrel

Origin: North America

No one knows how the grey squirrel arrived in Europe, whether it was by accident or brought in on purpose. But all can now agree that however it happened, the consequences were not good. First reported in 1948, they have become one of the most loathed animals in the UK. Coming from North America, they have brought a deadly virus with them - a virus they are immune to, but which the native red squirrels are not. This, plus the fact that they eat seven times more food than the locals means that they outcompete for resources against a vulnerable and now-limited population of reds. Matters are made even worse for the native reds by the fact that the native predators do not prey on the invaders. The populations today show no signs of slowing down, despite a campaign to eradicate them.

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Russian wheat aphid is listed (or ranked) 36 on the list The Most Damaging Invasive Species in the World
Russian Wheat Aphid

Origin: Southern Russia

Like any aphid, these do not bode well for any plant. In this case, it is wheat. The Russian wheat aphid is speculated to have arrived in the Americas from wheat that was imported to Mexico from South Africa. It was first found in Mexico city in 1980 and then, in 1986, in Texas. Within months they were found in 6 other states. Once arrived, the aphids spread quickly through the wheat-porducing regions of the US, clearly very happy and adaptable to the dry conditions of the High Plains. They inject their toxic saliva into the plant as they eat, stunting the growth and damaging the plant. The aphids caused hundreds to millions of dollars in wheat and barley production losses through reduced yields and pesticide treatment costs. Annual direct yield losses peaked at $274 million in 1988 but dropped to less than $10 million by 1993. These pest still appear periodically across the western US, requiring quick action before major crop loss.

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Killer Algae is listed (or ranked) 37 on the list The Most Damaging Invasive Species in the World
Killer Algae

Origin: Indian Ocean

With the fun name "Killer Algae", you know it's going to delightful. An invasive marine alga that is widely used as a decorative plant in aquariums, it was originally found in the Indian ocean. A cold-tolerant strain was inadvertently introduced into the Mediterranean Sea in wastewater from the Oceanographic Museum at Monaco, where it has now spread over more than 13,000 hectares of seabed. It forms dense colonies that prevent the establishment of native plants and excludes almost all marine life, affecting the livelihoods of local fishermen.  It contains a toxin that is not harmful to humans but may be lethal to certain species of fish and invertebrates and may interfere with the eggs of some marine organisms.  The plant appears unpalatable to general herbivores, and seems to grow unrestrained and develop into a dense, uniform carpet that blankets an area and persists from year to year.  Other marine life leaves the area, and there are even indications that it may kill off many microscopic organisms.  It has displaced rich habitats like eelgrass beds that sustain a complex food chain leaving the area unable to sustain a variety of life forms.  

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Light brown apple moth is listed (or ranked) 38 on the list The Most Damaging Invasive Species in the World
Light Brown Apple Moth

Origin: Australia

Originating in Australia, the moth made its debut in the U.S. in California around 2006 after first spreading to New Zealand, England, Ireland, and Hawaii through various commercial agricultural shipments during the 1800s-1900s. The larval state (the caterpillar) damages the plant by eating the leaves, buds, shoots, and fruit; which damages and deforms the plant. The greatest economic impact comes when the caterpillar eats the fruit and causes damage that makes the fruit unmarketable. It doesn't just feed off food crops either, it will damage ornamentals as well. To date, the US government has spent approximately $70 million. If eradication is unsuccessful and it does establish in California, the impact could be over $133 million per year (as estimated by CDFA). If you see this moth, please report it to local authorities.

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Ice Plant is listed (or ranked) 39 on the list The Most Damaging Invasive Species in the World
Ice Plant

Origin: South Africa

A coastal succulent that is native to South Africa, the iceplant was first brought to California in the early 1900s as an erosion stabilizer on railroad tracks. Later it was used along roadways and then as an ornamental. It is still sold in nurseries despite its invasive nature. It spreads easily and because it is very happy in a coastal clime, spreads fast. The problem arises when it establishes in a location it forms a thick, large mat that chokes out any other native plant in the area. On top of that, it alters the soil composition. This is bad news for many fragile, endangered and threatened coastal plants. There are eradication plans underway, but it is a difficult plant to remove, once established.

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Khapra Beetle is listed (or ranked) 40 on the list The Most Damaging Invasive Species in the World
Khapra Beetle

Origin: India

Among the worst of the worst of the world's invasive species, the khapra beetle is a serious pest of stored products. Infestations are hard to control because the beetle has a talent for living a long time without eating. They can crawl into the tiniest of cracks and remain there for long periods which helps them avoid surface insecticides. One of the only defenses against this invader is to never allow it come in the first place. Khapra is considered one of the world’ most destructive pests of grain products and seeds. The larval stage is the most detrimental. It can be found in warehouses, mills, breweries and malt factories. This is because it attacks all types of grain. The grain kernels are often hollowed out leaving nothing but the husk behind. To make things worse, the khapra beetle can reproduce so rapidly that containers of grain can become flooded with larvae, completely destroying all of the crop. Though it is established in many Mediterranean, Middle Eastern, Asian and African countries, it was also discovered in California in 1953, leading to a massive eradication effort which lasted 13 years and cost $15 million dollars. To date it has been successfully eradicated from each state it has been found, and inspectors have managed to catch it before it has reentered the US several times over the last decades.

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Big-Headed Ant is listed (or ranked) 41 on the list The Most Damaging Invasive Species in the World
Big-Headed Ant

Origin: Mauritius

Considered one of the world's worst invasive ant species, the big-headed ant is very aggressive and very good at multiplying because they employ more than one queen. Scientists have found them in more than 1,600 sites across the globe. When they arrive at a sufficiently warm destination, it spells almost certain doom for native ants, spiders, beetles, and other invertebrates that are unaccustomed to their brand of aggressive warfare. As the name implies, this ant's colonies include soldiers with disproportionately large heads. These giant, muscle-bound noggins power their mandibles, which they use to attack other ants and inverterbrates and cut up prey. They also harvest seeds and harbor phytophagous insects that reduce crop productivity. It is also known to chew on irrigation, electrical wire and telephone cables.

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Stoat is listed (or ranked) 42 on the list The Most Damaging Invasive Species in the World

Origin: The Americas, Eurasia

A sad story of biocontrol gone wrong, the stoat was originally introduced to New Zealand to take care of the rabbit invasion - another invasive that wreaked havoc when it was thoughtlessly introduced. The introduction of stoats was opposed by scientists in New Zealand and Britain, but the scientists’ warnings were ignored. A smart, opportunistic killer, the stoat is fearless in attacking animals larger than itself and adapting to shortage by storing surplus kills. Usually they eat mice and birds. It was the birds, not the rabbits that these stoats turned to when they were let loose in New Zealand. Six years after they were let loose, all bird populations faced a rapid decline, and to this day, the effects have been devastating on virtually all rodent and bird species – a testimony that introducing a non-native species into an ecosystem that has no defenses against it is not something to be taken lightly. Today, cost of research and management of stoats in New Zealand runs into millions of dollars a year.

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Small Asian Mongoose is listed (or ranked) 43 on the list The Most Damaging Invasive Species in the World
Small Asian Mongoose

Origin: India

Originally from India, the mongoose was brought to Puerto Rico and Hawaii initially to eat the rats and snakes that threatened sugar cane fields. However, brace yourself... it backfired. Instead of carefully killing only the nuisance animals, the mongoose became a terrorizing killing machine. It did kill a few rats, but had very little impact on the population as a whole. While the (invasive) rat was already endangering native populations of ground nesting birds, bringing the mongoose only added to the problem. The normal diet of a mongoose is largely made up of insects, but also includes small cats, snakes, frogs, rodents, seeds, nuts, fruit and, of course, the delicious egg. It has so far caused the extinction of 12 reptile and amphibian species from Puerto Rico, the West Indies and Jamaica. Unlike in India, its true home, the mongoose has no natural predators on these islands and is free to be its best, murderous self. Add in the fact that the mongoose (and the rat) carries leptospirosis which it transfers into streams and water supplies with its droppings, and it has become a threat to humans as well.

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Rainbow trout is listed (or ranked) 44 on the list The Most Damaging Invasive Species in the World

Origin: North America

One of the favorite sport fish in the world, these natives of North America can now be found on every continent in the world except Antarctica. Intentionally introduced all over to "improve" fish stocks, they are extremely competitive for resources and have been found to negatively impact native species. This adaptibility is made worse by their abilty to hybridize with other species, a fact that has led to the near-extinction of many other types of fish. Additionally, they have introduced whirling diesease to many populations, a parasite that causes fish to swim erratically and have a hard time eating. While some areas have eradication efforts underway, others are still stocking these fish for sport fishing and aquaculture despite the impacts on native fish.

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Coqui Tree Frog is listed (or ranked) 45 on the list The Most Damaging Invasive Species in the World
Coqui Tree Frog

Origin: Puerto Rico

Found in its native Puerto Rico, the coqui tree frog has spread to Hawaii via commercial nursery plants. As Hawaii is an island ecosystem full of thousands of endemic species, the coqui has had a catastrophic impact since its arrival in the late 80s. Unlike in Puerto Rice, these frogs have exploded in population - 2 frogs per square meter and sometimes over 4x that. They left behind their natural predators and now live in frog paradise with not a care in the world. Each frog eats about eight prey animals a day putting Hawai‘i’s endemic insect and spider species at risk and competing with endemic birds and other native fauna which rely on insects for food. There are also concerns that property value and tourism may be affected due to the high biomass of frogs on infested sites primarily because of how loud and annoying they are.

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Silverleaf whitefly is listed (or ranked) 46 on the list The Most Damaging Invasive Species in the World
Silverleaf whitefly

Origin: India

The silverleaf whitefly probably entered the US as early as 1897, but it wasn't until 100 years later that the more aggressive strand appeared. It is now considered an invasive pest in not only the US, but Australia, Africa and Europe. While tiny and actually quite pretty, this insect causes damage to plants first by feeding off them and secondarily transmitting disease. Not only do they damage the leaf and make the plant sick, they also produce honeydew - a sticky substance they leave behind on the plant that inhibits growth and results in lower yield and poor quality plants. These insects probably first left their native India on ornamental plants shipped overseas, a common method of transporting so many of the harmful invasives on this list. 

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Asian Long Horned Beetle is listed (or ranked) 47 on the list The Most Damaging Invasive Species in the World
Asian Long Horned Beetle

Origin: Asia

Originally from Asia, this beetle is at its most destructive during its larval stage. It has the ability to kill trees off with horrible effectiveness. The larvae tunnels and feeds on the layer of trees found between their bark and their wood. In large enough numbers, these larvae can eventually kill the tree. In the US, it has been estimated to potentially destroy 30.3% of urban trees and cause $669 billion in economic loss.They have spread globally, but early detection allows for immediate steps to be taken to eradicate them before their numbers can grow large enough to do serious damage. Once discovered and dealt with, infested areas are re-surveyed at least once per year for 3–5 years after the last beetle or infested tree is found.

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Chinese Creeper is listed (or ranked) 48 on the list The Most Damaging Invasive Species in the World
Chinese Creeper

Origin: Central and South America

Introduced into India after WWII to camouflage airfields, this slender perennial vine has become a major weed. It has become one of the most prolific and widespread invasive plants in the Pacific region. It kills or damages other plants by cutting off the light and smothering them after first competing for water and nutrients. It is also believed that it releases a substance that inhibits the growth of its competitors. It is considered one of the three worst weeds of tea in India and of rubber in Sri Lanka. It has caused the abandonment of coconut plantations in Samoa and it also causes serious issues in oil palm, banana, cacao and other forestry crops. Its seeds can be dispersed by wind and also on clothing or hair. Control of the creeper is difficult because it produces so many seeds, and because new plants can grow from even the tiniest stem fragments. Other than complete destruction of all the stems, herbicides provide the only suitable method of control at present though there are several methods of biocontrol that are being explored.

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Banana bunchy top virus is listed (or ranked) 49 on the list The Most Damaging Invasive Species in the World
Banana Bunchy Top Virus

First ID: Fiji

While all plant diseases that go after food crops are bad, the Banana Bunchy Top Virus has spread virulently through Asia, Taiwan, the Phillippines and the South Pacific thanks to aphids. As if aphids weren't already a scourge on their own. Once infected, the banana won't bear fruit. There is no species of banana yet found that can resist the disease, and there is no cure or vaccine. While it has arrived in Hawaii and been found in parts of India and Africa, it has not yet reached Central or South America. Hyper vigilance is required by agricultural inspectors, but aphids are tiny and easy to miss - it may just be a matter of time.

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Cogon grass is listed (or ranked) 50 on the list The Most Damaging Invasive Species in the World
Cogongrass

Origin: Asia

Considered one of the top ten worst weeds in the world and a pest in 73 countries, this grass is extremely hardy and able to adapt to poor soil, drought and fire. It has all the features of a truly menacing invasive. It affects local plant productivity and survival, wildlife habitat, recreation, native plants, fire behavior, site management costs and more. Its seed likely made its way out of Japan via packing materials and continued, controversial ornamental use has increased its spread. Cogongrass spreads by both seed and root fragmentation. Windblown seed can move several miles in air currents and plants can produce up to 3,000 seeds per season. Seed and rhizomes move even farther when hitchhiking on equipment, mulch, and fill materials. The plant forms a dense mat in the soil which makes control by mowing highly ineffective and can spread populations even further.