Top 10 Invasive Species in the United States

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Animal and plant species are uniquely adapted to their ecological niche. But where man goes, invasive species frequently follow, or at least hitch a ride. These invaders can cause millions of dollars in damage each year and may destroy native species and habitats. Ironically, some of these invasive species were introduced into the United States years ago to solve an environmental problem, before their destructive potential became apparent. Following are the 10 most troublesome invasive species wreaking havoc in the U.S., ranked according to several factors, including economic damage, the extent of their habitat and the potential for future damage to the economy and the environment.


10. Rusty Crayfish

The rusty crayfish poses a threat to native crayfish.
The rusty crayfish is a native of the Ohio River basin, but has spread to the Northeast and Upper Midwest, as well as other regions, where it eats fish eggs and displaces other crayfish species. Although most rusty crayfish are spread by fisherman using them as bait, the species has arrived in other areas in unexpected ways. For example, rusty crayfish apparently reached some states via shipments from science teaching-supply companies.


9. Africanized Bee

Africanized bees, better known as killer bees, can swarm with intensity.
A plot device for many bad Hollywood movies in the 1970s, Africanized (or “killer”) bees were introduced in South America in the 1950s as a means to increase honey production by interbreeding with native species. Africanized bees are now common in the Southern U.S. and will no doubt become more pervasive with climate change. They are not poisonous, but will swarm in great numbers if disturbed, as they are much more aggressive than the European honeybee.


8. Cane Toad

The cane toad kills an untold number of household pets each year in Florida.
Many residents of southern and central Florida do not realize they may have an invasive species right in their own backyard. The cane toad is a native of Central and South America and was introduced to Florida as a means to control white grubs in cane fields. The toad secretes a toxin when handled which will burn and irritate the skin, and it poses a threat to household pets, as an untold number of dogs and cats are killed by the frog’s poison each year. The cane toad’s introduction into Florida can be traced to an accidental release by an animal handler at the Miami airport in the mid-1950s.


7. Kudzu

Kudzu can grow up to a foot per day.
Brought to the United States in 1876 by a Japanese delegation to the Centennial Exposition in Philadelphia, kudzu was originally cultivated to feed livestock and prevent soil erosion. The problem is that the plant grows too well. Probably the most destructive threat kudzu poses is its potential to destroy other forest species by choking out needed sunlight. The clinging vine can grow up to a foot a day (yes, that’s an inch every two hours.) and has swiftly become known as the “Vine that Ate the South.” And as with many temperate species, expect kudzu to become more pervasive as warmer climates creep northward.


6. Fire Ant

The fire ant's bite sends hundreds of people to emergency rooms each year.
Anyone who has been bitten by fire ants will never forget the experience. Introduced to the U.S. from a South American cargo ship docked in Mobile, Alabama, in the 1930s, these pests are now a common feature in many backyards. The bite of the Red imported fire ant releases Solenopsin, a powerful alkaloid which often results in white pustules at the inflammation site and may take a year to heal. Fire ant bites send hundreds of people to the emergency room annually, as an estimated 30-60 percent of individuals living in fire-ant infested areas are bitten each year.


5. Formosan Termite

The formosan termite can quickly cause great structural damage.
A native of China, the Formosan Termite is now endemic in the Southeastern U.S. The termite is especially troublesome for homeowners because it can cause a huge amount of structural damage in a short period of time. After several years of growth, a colony will seek out timber within a 400-foot radius and establish secondary colonies. Formosan Termites have been known to destroy houses, boats, forests, and even power cables.


4. Zebra Mussel

The zebra mussel poses a serious threat to water intakes at hydroelectric and nuclear power plants.
A very destructive pest in the Great Lakes region, the striped Zebra mussel was originally introduced into the United States by foreign cargo ships releasing their ballast water. Zebra mussels wreck havoc by choking water pipes, constricting flow to nuclear and hydroelectric plants. Further spread of zebra mussels through U.S. waterways occurs when the pelagic or free-floating larval stage drift down river, or recreational boaters unwittingly carry the mussels from one lake to another attached to the hulls of their boats. Zebra mussels now can be found in 29 states.


3. Northern Snakehead

Credit: Brian Gratwicke

Credit: Brian Gratwicke

A voracious predator of other fish, the Northern Snakehead made its way from its native China to U.S. waterways via a Chinese soup remedy and has shown the capability to survive North American winters. This fish is also special for another reason; it can survive on land for up to four days and can travel from pond to pond by twisting and writhing its body across land. This adaptation allows them to propagate during droughts. They can also burrow and survive in mudflats for an extended period of time. Spread of the snakehead will mean further destruction of riparian ecosystems and damage to the fishing and tourism industries in this country.


2. Mediterranean Fruit Fly

The Mediterranean fruit fly caused $9.5 billion in damages to the California economy in 2005.

Credit: Scott Bauer/USDA

Robust and able to thrive in a variety of climates, the Mediterranean fruit fly is one of the top agricultural pests in the world. A single Medfly will pierce a fruit and lay about a dozen eggs, which become larvae, or maggots. The offspring devour the fruit from within and then hatch more Medflies. The Medfly has been established for more than 100 years in Hawaii, where efforts to halt the fly’s spread have ceased. The Medfly has also been found in California, Texas and Florida through the years, but efforts to control the insect, including quarantines, insecticides and the release of sterile flies, have eradicated the insect in those areas. Firm establishment of the Medfly would have devastating consequences for agriculture in any of those three states, especially California, where crops susceptible to the Medfly are a $10 billion annual industry. The United States Department of Agriculture estimates that the Medfly costs the state of Hawaii some $300 million each year in lost revenue from produce.


1. Asian Carp

Asian Carp jump out of the water in the Wabash River. Credit: Todd Davis/U.S. Army Corps of Engineers

Asian Carp jump out of the water in the Wabash River. Credit: Todd Davis/U.S. Army Corps of Engineers

Another waterway pest, the Asian Carp was first brought to the United States by catfish farmers in the 1970s as a means to control algae growth in their ponds. The carp soon reached the Mississippi River and have since caused damage to the ecosystem through their enormous consumption. Tens of millions of dollars have been spent in an effort to prevent the Asian Carp from spreading to the Great Lakes. On a bizarre note, the fish has become a sensation on YouTube, where videos show off the fish’s prolific ability to leap out of the water.

Written by

David Dickinson is a backyard astronomer, science educator and retired military veteran. He lives in Hudson, Fla., with his wife, Myscha, and their dog, Maggie. He blogs about astronomy, science and science fiction at