Mollusks Take Miami

South Florida gears up to eradicate a slimy invader.

April 18, 2013

In the 1950s, Hollywood deployed outsized versions of the familiar critters that flit and scuttle through the garden (think: The Fly, The Spider, and The Deadly Mantis) to terrorize science-fiction audiences

In September 2011, the Florida Department of Agriculture confirmed a true-life version of those creepy flicks in Miami-Dade County: an outbreak of the giant African land snail (GALS), a native of Kenya and Tanzania. Within 3 months, officials had collected more than 33,000 of the massive mollusks, whose bodies measure up to 8 inches and whose shells can grow larger than a child's fist. "They'd probably been around a couple of years," says spokesperson Denise Feiber. "We didn't find them the day they showed up."


With a diet that comprises more than 500 plant species, GALS (Achatina fulica)boast a prodigious appetite that puts both backyard landscaping and commercial agriculture at risk as populations rise. As with other snails, they favor seedlings, but they're not picky eaters. "In other countries where they've become established, they move through like an army," says Feiber, noting that without natural enemies they become a challenge to control once established. "They just eat every plant in sight." The snails' taste for calcium-rich foods--including concrete and stucco--to sustain growth of their conical, yellow-streaked, reddish-brown shells also puts buildings at risk.

In addition, GALS can be a menace on the road (hit one and the resulting slick can send a vehicle careening) and a health hazard in the kitchen (rat lungworm, a parasite that contaminates snail-slicked veggies and undercooked snail meat, causes a low-grade but still unpleasant version of human meningitis).

Left to their own devices, mature GALS can slink a distance of just 250 meters in a year, but their pea-sized eggs travel fast on contaminated plant material moved by unsuspecting humans. Live adults are transported (illegally, in the United States) for food, as pets, and for rites associated with African and Afro-Brazilian religious practices. The snails tolerate temperatures as low as 36°F, and although they can go dormant in suboptimal conditions, freezing temperatures kill them. Thus it is unlikely that they could become established in the continental United States north of USDA Plant Hardiness Zone 10.

The Global Invasive Species Database rates GALS "one of the worst snail pests of tropic and subtropic regions." Its reproductive potential is impressive: After mating just once, the hermaphroditic adults can store enough sperm to lay some 1,200 fertilized eggs over the course of a lifespan that can last nearly a decade.

In 1966, a woman released her grandson's three pet GALS--transported from Hawaii, where they've been established since the late 1930s--in her Miami garden. Officials captured more than 17,000 of their progeny over the next decade before declaring a $1 million eradication program a success. Midway through the program, the USDA had estimated that if the snails became established, annual costs associated with crop losses and agricultural control efforts would reach $11 million.

This time around, the state's department of agriculture has partnered with federal officials on a comprehensive effort that includes hand collection, community outreach and education, and use of an iron phosphate bait. "We don't assume it will be eradicated in 1 year," says Feiber. "We have to take it a step at a time, but we are optimistic."

Image: Andrew Derksen, FDACS/DPI,