An invasive species is an organism that came from somewhere else and can do harm to its new ecosystem. Invasive species can damage native areas, spread diseases, and cause extinctions of other animals.

In a new environment, an invasive species can suddenly take over. Their populations can grow quickly and crowd out native species. Invasive species can use up food and water. They often lack predators in their new home. In many cases, native species cannot compete against the new invader.

Not all species introduced to a new area are invasive. Sometimes, there are benefits to new species. For example, common foods, such as potatoes and tomatoes, came from the Americas. Explorers introduced them to the rest of the world through farming. An introduced species is only considered to be invasive if it causes harm.

Human Influence

Invasive species are almost always spread by humans. People and goods can move all over the planet. They often take invasive species with them. Often it is by accident.

As they traveled the globe, early explorers introduced many invasive species, such as dogs (Canis familiaris), cats (Felis catus), pigs, and rats. For example, Norway rats (Rattus norvegicus), also called brown rats, came from China. They spread to the Pacific Islands on ships during the 1700s. They eat native species and spread deadly diseases. Invasive feral pigs (Sus scrofa) live on the islands of Hawai'i in the United States. Feral pigs dig up plants and damage soil. Early Polynesian settlers might have brought the pigs for farming.

The Asian plant kudzu (Pueraria montana var. lobata) came to the U.S. during the 1876 World's Fair in Philadelphia, Pennsylvania. In the 1930s, people in the southern United States planted the fast-growing vine. They hoped this would prevent soil erosion. But the kudzu grew out of control.

Other times, invasive species were introduced to control pests. The cane toad (Bufo marinus) comes from South and Central America. It was introduced to Australia in the 1930s. People hoped the toad would eat pests in sugar cane plantations. But then the cane toads became a problem. The toad is toxic. It can be deadly to predators who try to eat it.

Trade and Travel Moves Invasive Species along

Today, we know more about what happens when we move organisms outside of their natural homes. We now try to keep them from spreading. But people continue to introduce invasive species through trade and travel.

For example, in the U.S. Florida Everglades, Burmese pythons (Python bivittatus) are causing problems. These snakes make popular pets but grow to be incredibly large. Owners have released them into the wild to get rid of them. The pythons eat local birds and even alligators. The Burmese python has no natural predators in Florida, so their population is thriving.

Lionfish live in the South Pacific and Indian Ocean. But they have quickly spread through the Atlantic Ocean, Gulf of Mexico, and the Caribbean Sea. Lionfish eat the native fish. They damage fisheries and coral reef ecosystems.

What Can Be Done?

Most countries have rules about what can and cannot be brought across their borders. Education is also important. Some invasive plants can be turned into paper. Some invasive fish such as lionfish can be eaten.

The invasive species problem was started by humans. But humans can also be part of the solution.