Invasive species are like an unwanted guest that you can't get out of your house.

Maybe it's an old high school pal. Or maybe a mother-in-law. Either way, we all know what it's like to invite someone into our home and not be able to get them to leave. They eat the food in the fridge. They take your favorite spot on the couch. And if they're a really good mooch, they'll take your bed and get you to sleep on the floor.

But what if they never leave? Or if they eat all your food? That's the real danger of invasive species. And it's a danger that threatens one of the state's most beloved trout streams.

Earlier this month, biologists confirmed the presence of New Zealand mudsnails in Centre County's famed Spring Creek.

It's bad news.

Although they aren't much larger than the tip of a pencil, the species has the potential to throw the creek's pristine ecosystem off balance. As an outsider, mudsnails will compete with native species for food and space.

Originally discovered in the United States in Wyoming's Snake River, this is the first time the slimy critters have been found in this section of the country. Given the popularity of Spring Creek, it's not surprising it's where the mudsnail made its first appearance in the Keystone State.

"Spring Creek is one of the most heavily fished streams in the state, with anglers traveling to it from all over the world," said Bob Morgan, an ecologist with the Fish and Boat Commission. "Given the presence of the mudsnail in other areas of the country, it's not surprising they have been found here."

Essentially, biologists suspect an angler accidentally introduced the mudsnail into the creek by not properly cleaning gear that was worn in a watershed with a prominent population of the invaders.

And now that the snails are here, they are likely here for good.

"As with many aquatic invasive species," Morgan continued, "they are nearly impossible to eradicate once established. This is even more difficult with the mudsnail because it usually takes only one small snail to be able to produce offspring. But we must do our best to slow its spread to other waters."

So what can you do to prevent mudsnails from spreading from Spring Creek to your favorite local creek? The simple answer is to clean your gear before leaving one body of water and again before entering another.

Mudsnails are tough. They need special eradication tactics. The simplest method is to soak your gear in Formula 409 for five minutes. If you have the freezer space you can also freeze your gear for at least six hours. Or, rather simply, you can soak your gear in hot water (over 120 degrees) for five minutes.

The unwanted visitor is already here. And most folks think mudsnails are here to stay. That means our job is to ensure the nuisance doesn't spread to more local waterways.

It's bad enough when we can't get a visitor to leave our home. But we certainly don't want the mooches to invite their cousins to our neighbors' houses.

Andy Snyder writes about dirt-track racing for The York Dispatch. He can be reached at sports@yorkdispatch.com.