Ifyou picnic in a Texas park, chances are you’ll encounter fire ants

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If you picnic in a Texas park, chances are you’ll encounter fire ants — a kind of pest that can deliver painful bites. This invasive (入侵的) species, like many others, is not only annoying but also destructive.

An invasive species is any kind of living thing that isn’t native to an ecosystem and causes harm. Sometimes non-native species are imported by accident, like in the 1930s when ships from South America inadvertently took fire ants to North America. Other times non-native species are imported deliberately. Some types of Asian fish that were originally imported to the U.S. from China to clean fish farms escaped and entered rivers. Green iguanas were brought to China, as pets, but irresponsible owners released them.

Non-native species have even been imported for emotional reasons. A man once released dozens of European starlings (八哥) in New York in an effort to bring all the birds mentioned in Shakespeare’s writings to America. Today, millions of starlings cause over $800 million in damage to U.S. agriculture every year. Invasive species’ global economic influence is also enormous. The U.S. government assesses that invasive species cost the American economy over $120 billion every year.

Invasive species can damage their host habitats by unbalancing local ecosystems. They often lack natural enemies in their new environment and out-compete native species for food and other resources. They also might feed on local species. Invasive species can also carry diseases for which local species have no immunity (免疫力). This can result in the loss of an entire native species.

Invasive species are among the leading threats to native wildlife. About 42% of threatened or endangered species are at risk due to invasive species. Unless people take serious action, the economic and environmental costs of invasive species will become disastrous.

【小题1】What does the underlined word “inadvertently” mean in paragraph 2?