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Fish, frogs and hogs: 10 of the most invasive species in America

Oct. 10, 2019Updated June 8, 2025, 12:37 p.m. ET
Invasive species such as the wild boar, shown here, impact various ecosystems all over the U.S., according to the Department of Agriculture.
Invasive species such as the wild boar, shown here, impact various ecosystems all over the U.S., according to the Department of Agriculture.
Andrew West, The News-Press Via USA Today Network
2. Alewife: These small silver fish are native to the Atlantic Ocean, but became introduced in large numbers when they took over Lake Eerie back in the 1800s. Today, they have a great impact on all of the Great Lakes, as well as bodies of water on the US east coast.
2. Alewife: These small silver fish are native to the Atlantic Ocean, but became introduced in large numbers when they took over Lake Eerie back in the 1800s. Today, they have a great impact on all of the Great Lakes, as well as bodies of water on the US east coast.
Greg Derr, The Patriot Ledger Via USA TODAY NETWORK
3. Bullfrog: The bullfrog serves as an invasive species to the US west coast, as it's originally native to the east coast. It was introduced accidentally during trout trades in the early 1900s.
3. Bullfrog: The bullfrog serves as an invasive species to the US west coast, as it's originally native to the east coast. It was introduced accidentally during trout trades in the early 1900s.
Kelly Wilkinson, USA TODAY NETWORK
4. Nutria: The swamp rodent "nutria" first established itself in the US in the 1930s, migrating north from South America. It is famous for destroying habitats in wetlands.
4. Nutria: The swamp rodent "nutria" first established itself in the US in the 1930s, migrating north from South America. It is famous for destroying habitats in wetlands.
Nick De La Torre, Houston Chronicle Via Getty Images
5. Burmese python: This mega snake is native to southeastern Asia. Large populations began to get noticed in the US in the early 2000s, thanks to a pet trade.
5. Burmese python: This mega snake is native to southeastern Asia. Large populations began to get noticed in the US in the early 2000s, thanks to a pet trade.
Robert Sullivan, AFP/Getty Images
6. Lion fish: The aquarium trade brought the lion fish to America in the 1980s from its native habitat in the Pacific Ocean. The fish's venomous spines have helped it invade the habitats of other native species.
6. Lion fish: The aquarium trade brought the lion fish to America in the 1980s from its native habitat in the Pacific Ocean. The fish's venomous spines have helped it invade the habitats of other native species.
Benjamin Lowy, Getty Images
7. Sea lamprey: The sea lamprey was first discovered in Lake Ontario in 1835, and slowly spread to other Great Lakes during the early 20th century.
7. Sea lamprey: The sea lamprey was first discovered in Lake Ontario in 1835, and slowly spread to other Great Lakes during the early 20th century.
Susan Tusa, Detroit Free Press
8. Brown tree snake: This snake is an invasive species to Guam, a US territory. Its introduction to the island is believed to be due to cargo trade from Indonesia, Australia or Papa New Guinea. Brown tree snakes often are aggressive toward native species, thus disrupting native habitats. The snake's ability to climb also often will create power outages, as it climbs electrical poles and equipment.
8. Brown tree snake: This snake is an invasive species to Guam, a US territory. Its introduction to the island is believed to be due to cargo trade from Indonesia, Australia or Papa New Guinea. Brown tree snakes often are aggressive toward native species, thus disrupting native habitats. The snake's ability to climb also often will create power outages, as it climbs electrical poles and equipment.
Rick Cruz, PDN Via USA TODAY Network
9. Cane toad: The cane toad was brought to the US in 1936 to control sugar cane pests in Florida. It is extremely toxic to predators.
9. Cane toad: The cane toad was brought to the US in 1936 to control sugar cane pests in Florida. It is extremely toxic to predators.
Austrailian Reptile Park, AFP/Getty Images
10. Asian swamp eel: This species of eel is native to Asia, but was imported to the US as a food source for the aquarium trade. Today, it's extremely competitive to native species.
10. Asian swamp eel: This species of eel is native to Asia, but was imported to the US as a food source for the aquarium trade. Today, it's extremely competitive to native species.
PHOTO PROVIDED BY UNIVERSITY OF FLORIDA/IFAS
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