Achatina fulica
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| East African Land Snail | ||||||||||||||||
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| Achatina fulica [1] (Férussac, 1821) |
The East African Land Snail, Achatina fulica, is a terrestrial pulmonate snail species that has been widely introduced to Asia, to Pacific and Indian Oceans islands, and to the West Indies. It has also been intercepted widely by quarantine officials and incipient invasions have been eradicated, for instance in the mainland USA. [2]
More recently, the land snail has become a common pet, however they are illegal in some countries including the United States [3]. They are easy and cheap to keep, and if bred in captivity, are unlikely to carry any parasites.
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[edit] Description
A very large snail, adults are usually around 7-8 cm (2.7 inches) tall, and can reach 20 cm (7.9 inches) in length or more. The shell has a rounded conical shape, being about twice as high as it is broad. Either clockwise (sinistral) or anti-clockwise (dextral) directions can be observed in the coiling of the shell, although a right-handed (dextral) cone is more common.
Colouration is highly variable, and dependent on diet. Generally the shell is banded (representative of variations in diet as the snail grows). Typically, the predominant colour is brown.
[edit] Habitat
The East African Land Snail is native to East Africa, especially Kenya and Tanzania, but also include most regions of the humid tropics, including many Pacific islands, southern and eastern Asia, and the Caribbean. They are a highly invasive species, and colonies can be formed from a single gravid individual. The species has established itself in Temperate Climates also, and in many places, release into the wild is illegal. The Giant East African Snail can now be found in agricultural areas, coastland, disturbed areas, natural forest, planted forests, riparian zones, scrub/shrublands, urban areas, and wetlands. They are active at night and spend the day buried underground.
[edit] Nutrition
The Giant East African Snail is a macrophytophagous herbivore meaning it eats a wide range of plant material, fruit and vegetables. Sometimes they eat sand, very small stones, bones from carcasses and even concrete as calcium sources for its shell. In rare instances they will consume each other.
In captivity, this species can also be fed on grain products such as brown bread, digestive biscuits and chicken feed. As with all molluscs, East African Land Snails enjoy the yeast in beer; it actually serves as a growth stimulus.
[edit] Reproduction
The Giant East African Snail is a simultaneous hermaphrodite, meaning each individual has both testes and ovaries. This means it is capable of producing both sperm and ova. Instances of self fertilisation are rare, and only occur in low populations. Although both snails in a mating pair can simultaneously transfer both gametes to each other (bilateral mating), this is dependent on the size difference between the partners. Snails of a similar size will reproduce in this way, however 2 of differing sizes will mate unilaterally (one way), with the larger individual acting as a female. This is due to the comparative resource investment associated with the different genders. Like other land snails, they have intriguing mating behavior, including petting their heads and front parts against each other. Courtship can last up to half an hour, and the actual transfer of gametes can last for 2 hours. A female can store sperm within her body for up to 2 years. The number of eggs per clutch averages around 200. A snail would lay 5-6 clutches per year with a hatching viability of about 90%.
[edit] Life cycle
Adult size is reached in about six months; after this period growth slows, but does not ever cease. The weight of the shell is directly proportional to the weight of the body, and in large individuals proves impervious to predators, except for carnivorous snails, who bore through the shell using their radulla, a tongue like organ. The life expectancy is around five or six years in captivity, but they may live up to ten years. The East African Land Snail is capable of aestivating for up to 3 years in times of extreme drought, sealing itself into its shell by secreting a calcerous compound that dries on contact with the air. This is impermeable, meaning the snail will not lose any water during this period.
[edit] Population control
Suggested preventative measures must include strict quarantine measures to prevent introduction and further spread. Many methods have been tried to eradicate the Giant East African Snail. Generally, none of them have been effective except where implemented at the first sign of infestation. Methods include hand collecting, use of molluscicides, flame-throwers, and the failed attempts at biological control discussed below. In some regions, an effort has been made to promote use of the Giant East African Snail as a food resource, collecting the snails for food being seen as a method of controlling them. However, promoting a pest in this way is a controversial measure, as it may encourage the further deliberate spread of the snails.
One particularly catastrophic attempt to biologically control this species occurred on South Pacific Islands. Colonies of A. fulica were originally introduced as a food reserve for American GI's during the second world war, but naturally escaped. A carnivorous species from East Africa, a known predator of the East African Land Snail was introduced, but instead heavily predated the native Partula, causing the loss of some species.[citation needed]
[edit] Notes
- ^ Achatina fulica (TSN 76978). Integrated Taxonomic Information System. Retrieved on July 6, 2007.
- ^ http://www.pbs.org/saf/1204/features/nature.htm PBS "Alien Invasion". Accessed on 6 January 2008
- ^ Should Giant African Land Snails Be Kept as Pets At All?
[edit] References
- Mead, Albert R. 1961. The Giant African Snail: A Problem in Economic Malacology. Univ. Chicago Press, 257 pp. (also available online)
- Global Invasive Species Database
- Achatina fulica in Captivity
