The National Park Service says invasive species are posing challenges to natural ecosystems, leading to threats to native wildlife and even humans.

Rangers say some of the invasive pests have been introduced accidentally, while others have been intentionally released into the wild.

Regardless of how they arrived, wildlife experts say their spread costs billions of dollars annually and leads to ecological harm.

Some of the most problematic species include stray and feral cats, beetles and even ants.

WHY BUYING LOCAL FIREWOOD CAN LIMIT THE SPREAD OF INVASIVE SPECIES

The NPS considers free-ranging cats to be among the widespread invasive problems throughout more than 400 sites.

While cats that are kept indoors do not pose any risks, abandoned cats have been linked to declines in bird, r

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