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 acrossthe spiral. Coloration is highly variable, depending on diet. A mature snailaverages 250 g in weight.
The species originated in thecoastal regions of East Africa (Kenya, Tanzania), and spread by the 19thcentury into Southern Ethiopia, Southern Somalia, and Northern Mozambique.During the 19th century it was introduced into India and the Indian Oceanislands.
During the 20th century it wasintroduced, sometimes intentionally, into South East Asia, East Asia (Taiwan,Korea, and Japan), Australasia and the Pacific, the USA (now eradicated invarious states), the Caribbean, Central America and South America (Brazil).
The species is highlyadaptable to a wide range of environments, modifying its life cycle to suitlocal conditions.
Reproduction:Without delays because of aestivation or hibernation, snails will reach sexualmaturity in less than a year (even as early as 5 months under laboratoryconditions). Reciprocal copulation (6-8 hours) must occur to produce viableeggs.
Laying: Thesmall (4 mm in diameter) yellowish-white eggs are laid in clutches of 10-400eggs 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 eachsnail.
Egg laying frequency dependson climate, particularly on frequency and duration of the rainy seasons: up to500 eggs per year in Sri Lanka, 300 per year in Hong Kong, and 1000 per year inCalcutta.
Hatchlings: Uponhatching, the hatchlings consume their eggshells (and unhatched siblings),remaining underground for 5-15 days and feeding on organic detritus. Eventuallythey 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 toplants.
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.
Significanceas a Pest
The species causesconsiderable economic damage to a wide variety of commercial crops. In mostparts of the world, the amount of dam-age is greatest when the species is firstestablished; during this period, snails are usually very large and theirpopulations can become immense. This is followed by a stable population phase,and then finally a period of decline.
Achatina fulica is reported tobe an intermediate vector of the rat lungworm Angiostrongylus cantonensis,which can cause eosinophilic meningoencephalitis in humans; as well as of agram-negative bacterium, Aeromonas hydrophila, which can cause a wide varietyof symptoms, especially in persons with compromised immune systems.