More than 1,000 of the mollusks are being caught each week in Miami-Dade and 117,000 in total since the first snail was spotted by a homeowner in September 2011, said Denise Feiber, a spokeswoman for the Florida Department of Agriculture and Consumer Services.
Residents will soon likely begin encountering them more often, crunching them underfoot as the snails emerge from underground hibernation at the start of the state's rainy season in just seven weeks, Feiber said.
The snails attack "over 500 known species of plants ... pretty much anything that's in their path and green," Feiber said.
In some Caribbean countries, such as Barbados, which are overrun with the creatures, the snails' shells blow out tires on the highway and turn into hurling projectiles from lawnmower blades, while their slime and excrement coat walls and pavement.
"It becomes a slick mess," Feiber said.
A typical snail can produce about 1,200 eggs a year and the creatures are a particular pest in homes because of their fondness for stucco, devoured for the calcium content they need for their shells.
The snails also carry a parasitic rat lungworm that can cause illness in humans, including a form of meningitis, Feiber said, although no such cases have yet been identified in the United States.
The snails' saga is something of a sequel to the Florida horror show of exotic species invasions, including the well-known infestation of giant Burmese pythons, which became established in the Everglades in 2000. There is a long list of destructive non-native species that thrive in the state's moist, subtropical climate.
Experts gathered last week in Gainesville, Florida, for a Giant African Land Snail Science Symposium, to seek the best ways to eradicate the mollusks, including use of a stronger bait approved recently by the federal government.
Feiber said investigators were trying to trace the snail infestation source. One possibility being examined is a Miami Santeria group, a religion with West African and Caribbean roots, which was found in 2010 to be using the large snails in its rituals, she said. But many exotic species come into the United States unintentionally in freight or tourists' baggage.
"If you got a ham sandwich in Jamaica or the Dominican Republic, or an orange, and you didn't eat it all and you bring it back into the States and then you discard it, at some point, things can emerge from those products," Feiber said.
Authorities are expanding a series of announcements on buses, billboards and in movie theaters urging the public to be on the lookout.
The last known Florida invasion of the giant mollusks occurred in 1966, when a boy returning to Miami from a vacation in Hawaii brought back three of them, possibly in his jacket pockets. His grandmother eventually released the snails into her garden where the population grew in seven years to 17,000 snails. The state spent $1 million and 10 years eradicating them.
Feiber said many people unfamiliar with the danger viewed the snails as cute pets.
"They're huge, they move around, they look like they're looking at you ... communicating with you, and people enjoy them for that," Feiber said. "But they don't realize the devastation they can create if they are released into the environment where they don't have any natural enemies and they thrive."