Florida is the land of invasive species. Because of our status as a center for the importing of exotic pets and houseplants from overseas, and our neo-tropical climate, we have been invaded by everything from kudzu plants to Burmese pythons. One of our most recent invaders is a giant snail that will not only eat your yard, but your house, too.
Giant African Land Snail. Photo by Wiki Commons.
The Giant African Land Snail (GALS, for short) lives up to its name. The cone-shaped spiral shell is fist-sized, and the snail within can measure over eight inches, making it one of the largest land snails in the world. Achatina fulica (some authorities classify it in the genus Lissachatina instead) is one of three species of giant land snail. Native to Tanzania and Kenya, these huge mollusks are plant-eaters, feeding on live or dead vegetation. To obtain the calcium they require for their shells, they will also eat pebbles, animal bones, cement, or the plaster stucco from houses.
Like most snails, GALS are hermaphrodites--that is, each individual has both male and female sex organs. When breeding, two individuals that are about the same size will fertilize each other, and both will then lay eggs. If the snails are unequal in size, the smaller one will fertilize the larger, who will play the role of the female. The courtship display involves lots of head-rubbing and neck-twining. Each clutch can contain two hundred eggs, laid every two months, and youngsters can reach sexual maturity in five months. Adults can live up to nine years.
The Giant African Land Snail can survive virtually anywhere where warm and humid conditions can be found. They are mostly nocturnal and spend the day buried in the ground to conserve moisture. In dry times of the year, the snails secrete a calcaneous plug for their shell that seals them in and prevents them from drying out.
From the early 1800s, GALS were imported and farmed as a food source, which had led to its escape and introduction as an invasive. One of the first places invaded was Nigeria, where the Achatina snails crowded out most of the native snail species. By 1936, the Giant African Snails had become established in China, Taiwan, and several Pacific islands, including Hawaii. The Second World War helped spread the snails, both by shipping them as food for troops, and by moving unseen stowaways. The snail is also used in ceremonies and rituals by several native religious sects, including Santeria and Candomble. Religious groups have inadvertently introduced escapees into Brazil and the Carribbean islands. In the early 2000's, the snails were briefly popular in the exotic pet trade, especially as classroom display animals, and although the US (and most other countries) has passed laws banning their import or possession, some number of snails are still being illegally smuggled into the US as pets each year. Today invasive populations are found all over Africa, South America, Asia and Australia.
Once established, the snails become serious agricultural pests. They are listed as one of the "100 Worst Invasives".
Florida's first encounter with the Giant African Land Snail was in 1966, when a young boy who visited his grandmother in Hawaii brought three snails home with him to Miami and released them in his backyard. Within five years there were thousands of them spread over miles, and the state embarked on a million-dollar eradication effort that eventually took ten years, but succeeded--the only time on record that a GALS infestation was successfully removed.
But in September 2011, the snails were back again, now in the Coral Gables area. No one is sure how they got there this time--it may have been from illegal pets, or it may have been an escape from a local Santeria group that was found using the snails in its rituals. In any case, the snails have bred rapidly. Though so far they are limited to a small geographic area in Dade County, state officials have already removed and killed over 130,000 individual snails. They have been found at densities of over 2,000 individuals per square mile. A team of snail-hunters from Florida's Department of Agriculture (they have a staff of 40 people devoted to eradicating the snails) uses traps, poison-bait, and specially-trained sniffing dogs to find the mollusks. (The poisons don't work so well--the snails, like rats, are able to learn if they get sick from eating something and won't eat it again.)
Unlike most invasive species, however, this one is a fight that Florida seems to be winning. Thanks to the massive eradication effort, the GALS invasion has remained confined to a small geographic area, and their numbers seem to be declining.
And now it's your turn--let us know what is going on in your neck of the woods. Seen any one-pound foot-long snails lately? :)