Lissachatina fulica

Giant African Snail
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Order:	Pulmonata
Family:	Achatinidae
Genus:	Achatina
Species:	A. fulica
Binomial name
Achatina fulica (Férussac, 1821)

The Giant African Snail, Achatina fulica, 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. It is a major agricultural and garden pest, and a general nuisance. It is also a vector (as are many snail species) of several human pathogens and parasites. Often its introduction leads to the subsequent introduction of predatory snails and, more recently, flatworms as putative biological control agents that can have devastating effects on native land snail diversity.

More recently, the land snail has become a common pet, however are illegal in some countries including the United States [1]. They are easy and cheap to keep, and if bred in captivity, are unlikely to carry any parasites.

Description

A very large snail, adults are usually around 7-8 cm tall, and can reach 20 cm in length or more. The shell has a rounded conical shape, being about twice as high as it is broad. The shell is generally brown in color with irregular darker treaks running transversely across the whorls.

Habitat

The Giant African 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. The Giant 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.

Disease

The Giant African Snail is also a vector of Angiostrongylus cantonensis (Nematoda; Protostrongylidae) or "Rat Lungworm", the roundworm responsible for eosinophilic meningo-encephalitis in humans and the spread of the disease has been correlated with the spread of the snail. However, many other introduced snails in the tropics are also vectors of this parasite and the spread of the disease has not definitively been related to the spread of the Giant African Snail.

The more insidious conservation problem they cause is that they tempt agricultural officials to initiate a number of putative biological control measures. The most well publicised of these measures is the introduction of predatory snails, most notably Euglandina rosea. The first attempts at such biological control were made in Hawaii. Fifteen carnivorous snail species were deliberately introduced. Of these, nine did not become established; the fate of three is unknown but they are certainly not common and do not appear to be causing serious problems. However, three have become established: Euglandina rosea, Gonaxis kibweziensis, Gonaxis quadrilateralis. There is no scientific evidence that the predatory snails are the reason for the observed decline in numbers of the Giant African Snail, however.

Similar ill-conceived attempts at biological control involving Euglandina rosea in particular have been implemented in French Polynesia, American Samoa, Guam, and a number of other places in the Pacific and Indian Oceans. In addition to the deliberate introduction of predatory snails, the predatory flatworm Platydemus manokwari has also been introduced, although as yet less widely. It is reported that this flatworm can indeed cause populations of the Giant African Snail to decline, but the evidence is only correlative, not convincingly causative. However, the flatworm has also been implicated in the decline of native species on Guam. It cannot be stressed enough that these introductions of putative biological control agents against the giant African snail are extremely dangerous from the perspective of the conservation of native snail species, and in any case, there is no good evidence that they can indeed control Giant African Snail populations.

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 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 above. In some regions, an effort has been made to promote use of the Giant 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.

Nutrition

The Giant African Snail is a macrophytophagous herbivore meaning it eats a wide range of plant material, fruit and vegetables.

Reproduction

The Giant African Snail is a cross-fertilizing, egg-laying hermaphrodite. Like other land snail, they have intriguing mating behavior, including petting their heads and front parts against each other not unlike humans. 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%.

Life cycle

Adult size is reached in about four months, but growth may continue slowly beyond this up to at least one and a half years. The life expectancy is around five or six years in captivity, but they may live up to ten years.

References

• Public domain information from:
  • Global Invasive Species Database
  • Related Disclaimer
• The Giant African Snail: A Problem in Economic Malacology (online full-text book)
• Snailsonline
• Achatina fulica in Captivity

ij