They crawl up the walls. Slowly.

Very slowly.

They hide in the grass, moving, and eating, at night.

And not so slowly, South Florida is under attack. And Olga Garcia’s job is to save neighborhoods.

"This is the Giant African Land Snail, invading Miami,” she says, as she places another 3-inch long snail into a steadily filling bag.

In just the past 5 weeks, teams of pest hunters have captured about 30,000 of these invasive African snails. They have a taste and insatiable appetite for 500 species of plant, they destroy the walls of houses and they transport meningitis, threatening Florida agriculture, real estate and human health.

"When there's a report of an invasive pest, we say 'what's next? When will be the next one?' because it seems it never stops," says Jorge Pena of the University of Florida. He and his microscope are constantly looking for pests from other places. Scientists estimate the damage done nationally by invaders like the Red Ambrosia Bay Beetle, the Red Palm Mite and Ficus White Flies is in the billions of dollars a year.

The Department of Homeland Security concedes agriculture inspections dipped after 9/11—as port inspections focused more on terrorism—but the DHS says, today, its 2,600 pest inspectors are fully focused on the nation’s food supply; what’s being imported, from where and what particular pests could be hitching a ride. DHS reported last year that its inspectors caught and submitted 200,000 pests.

All of this matters extraordinarily for farmers and consumers, translating to profits and prices.

“We’re fearful every day,” says Neil Brooks, owner of Brooks Tropicals in Homestead, Florida. He’s Florida’s number one producer of avocados. He used to be the largest producer of limes, but the canker bacteria which entered the U.S. from Southeast Asia in the past decade infected his lime trees with disease, wiping out his business.

“Any new insect, new disease, that is not present in other states in the U.S. will lead to a quarantine of this county, or this state. For me, it’s the loss of all the groves.”

In Florida, on average, one new invasive species is discovered every month. And with increased global trade, and personal travel, experts see a future with pests from other places as inevitable.

And typically, once they arrive, there is no natural predator.

And that’s why the Giant Land Snails are reproducing, well, like rabbits.

Phil Keating joined Fox News Channel (FNC) in March 2004 and currently serves as FNC's Miami-based correspondent.