Alien Species

This passage is about how alien species spread.

Lexile Level: 1150L

Categories: Animals & Nature


Alien species are a growing threat to the health and diversity of the world's ecosystems. Alien species are plants and animals that become established outside of their natural range as a result of human activity such as tourism or trade. Once established, alien species can have a devastating effect. They compete with native species for food and space, they prey upon native populations, and they often have no natural predators, so their population can grow unchecked. One of the most aggressive alien species to arrive in the United States in recent years is the snakehead fish. It feasts on smaller fish, it can grow to more than three feet in length, and it can move on land. The snakehead uses its fins to crawl short distances between bodies of water and can thus spread quickly. Once an alien species becomes established, it is almost impossible to eradicate. Biologists warn people never to release any alien species in the wild.


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