Environment: Tale of a Snail

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Before flying home from a Hawaiian vacation with his family in 1966, a five-year-old Miami boy packed some unusual souvenirs. Hawaii's pest-control agents waved the lad through Honolulu International Airport—never suspecting that he was lugging three brown-shelled snails. Soon after reaching home, his mother ordered him to toss the creatures into his backyard. What he tossed was an ecological bombshell. Innocently, the boy had introduced into the mainland U.S. a ferociously fertile predator: Achatina fulica, more commonly known as the giant African land snail.

By now, at least 20,000 of the fist-size mollusks infest a 50-acre residential section of North Miami; more have been spotted in Hollywood ten miles to the north. Tough, ravenous creatures, whose original home is East Africa, they have chewed up large stretches of grass, stripped the bark off trees, feasted on citrus plants and even devoured paint off buildings—a handy source of calcium for snails' shells.

Uphill Fight. North Miamians can no longer walk across their lawns without crunching shells underfoot, and the snail outbreak may get still worse. Endowed with both male and female reproductive organs, the hermaphroditic snail multiplies at a phenomenal rate. In his authoritative study The Giant African Snail, University of Arizona Malacologist Albert R. Mead calculates that a single animal could theoretically produce 8 billion descendants in three years. Such spectacular proliferation requires a huge food supply—for example, Florida's luxuriant cash crops.

State pest-controllers are mobilizing against the marching marauders, but they face an uphill fight. Achatina, whose body can grow as long as a foot, has so few natural enemies that it can roam almost anywhere. Plagued by other recent invaders—the Bufo toad from Central America and the Asian walking catfish—Florida biologists are reluctant to import any anti-snail predators, such as the India glowworm, the hermit crab, or even more Bufos, which are known to feed on the young snails. Instead, they have begun careful spraying with insecticide (granules of metaldehyde mixed with tricalcium arsenide). So far, the chemical warfare seems effective. But the snail threat will not abate until the last Achatina is vanquished—which is hardly an immediate prospect.