Achatina fulica (garden snail, foolish snail) is a large snail, reaching 20 cm in length or occasionally more, with a shell length up to 20 cm and a maximum diameter of 12 cm. The conical, spiraled shell is predominantly brown with weak, darker banded markings across the spiral. Coloration is highly variable, depending on diet. A mature snail averages 250 g in weight.
The species originated in the coastal regions of East Africa (Kenya, Tanzania), and spread by the 19th century into Southern Ethiopia, Southern Somalia, and Northern Mozambique. During the 19th century it was introduced into India and the Indian Ocean islands.
During the 20th century it was introduced, sometimes intentionally, into South East Asia, East Asia (Taiwan, Korea, and Japan), Australasia and the Pacific, the USA (now eradicated in various states), the Caribbean, Central America and South America (Brazil).
The species is highly adaptable to a wide range of environments, modifying its life cycle to suit local conditions.
Reproduction: Without delays because of aestivation or hibernation, snails will reach sexual maturity in less than a year (even as early as 5 months under laboratory conditions). Reciprocal copulation (6-8 hours) must occur to produce viable eggs.
Laying: The small (4 mm in diameter) yellowish-white eggs are laid in clutches of 10-400 eggs within 8-20 days of copulation, usually in nests excavated in the soil. Repeated laying may result from one copulation, as sperm is stored in each snail.
Egg laying frequency depends on climate, particularly on frequency and duration of the rainy seasons: up to 500 eggs per year in Sri Lanka, 300 per year in Hong Kong, and 1000 per year in Calcutta.
Hatchlings: Upon hatching, the hatchlings consume their eggshells (and unhatched siblings), remaining underground for 5-15 days and feeding on organic detritus. Eventually they feed primarily on plants at night, returning to roost before dawn.
Juveniles: Animals with shell lengths of 5-30 mm apparently cause the most damage to plants.
Adults: The snails may reach sexual maturity in less than a year. Larger snails continue to feed on plant materials, but feed increasingly on detritus as they age. Normally, they live for 3-5 years.
Significance as a Pest
The species causes considerable economic damage to a wide variety of commercial crops. In most parts of the world, the amount of dam-age is greatest when the species is first established; during this period, snails are usually very large and their populations can become immense. This is followed by a stable population phase, and then finally a period of decline.
Achatina fulica is reported to be an intermediate vector of the rat lungworm Angiostrongylus cantonensis, which can cause eosinophilic meningoencephalitis in humans; as well as of a gram-negative bacterium, Aeromonas hydrophila, which can cause a wide variety of symptoms, especially in persons with compromised immune systems.