Taxonomic name: Achatina fulica Bowdich, 1822
Synonyms:
Common names: achatine (French), Afrikanische Riesenschnecke (German), escargot géant d'Afrique (French), giant African land snail, giant African snail (English)
Organism type: mollusc Achatina fulica is a threat to the sustainability of crop systems and native ecosystems, having a variety of negative impacts on native fauna, from competition for resources to the spread of diseases to direct herbivory of native plants. Native snails in fragile island ecosystems such as Hawaii and the French Polynesian islands are particularly susceptible to the negative effects of Achatina fulica and other introduced snails. Occurs in:
agricultural areas, coastland, natural forests, planted forests, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands Habitat description
All of the countries in which Achatina fulica is established have tropical climates with warm, mild year-round temperatures and high humidity (Venette and Larson 2004). The species occurs in agricultural areas, coastal areas and wetlands, disturbed areas, natural and planted forests, riparian zones, scrublands and shrublands, and urban areas (Moore 2005). These snails thrive in forest edge, modified forest, and plantation habitats (Raut and Barker 2002). Wherever it occurs, the snail keeps to the hot lowlands and the warm temperate lower slopes of the mountains. It needs temperatures well above freezing year round, and high humidity at least during part of the year, the drier months being spent in dormant aestivation. It is killed by sunshine (Venette and Larson 2004). A. fulica remains active at a temperature range of 9°C to 29°C, and survives temperatures of 2°C by hibernation and 30°C by aestivation (Smith and Fowler 2003). General impacts
Achatina fulica is considered one of the worst snail pests in the tropics and subtropics. It consumes large volumes of native plants, modifies habitats and out-competes native snails (Moore 2005). Achatina fulica may also effect native ecosystems by altering the food chain by providing an alternative food source for predators (Mead 1961). This can have unfortunate consequences if the predator species is also invasive. For example, in the Bonin Islands, Japan, the introduced invasive toad (Bufo marinus) was found to prey predominantly on Achatina fulica (Matsumoto et al. 1984). However, natural predation may alternatively help keep populations of Achatina fulica in check. For example, on the Christmas Islands Achatina fulica has not established in undisturbed rainforests; this is thought to be due to native red crabs consuming significant numbers of the snail (Lake and O'Dowd 1991).
Achatina fulica is a major agricultural pest, feeding on a variety of crops and causing significant economic losses. In the US state of Florida it has been estimated that Achatina fulica would have caused an annual loss of $US11 million in 1969 if its population had not been controlled (USDA 1982). In India it attained serious pest status, particularly in 1946/47, when it appeared in epidemic proportions in Orissa and caused severe damage to vegetable crops and rice paddies (Pallewatta, Reaser and Gutierrez 2002). Plants most likely damaged by the snail are garden flowers and ornamentals, vegetables, (especially Cruciferae, Cucurbitaceae and Leguminosae) and immature specimens of breadfruit, cassava and teakwood. Achatina fulica may also increase the spread of plant diseases (for example, black pod disease caused by Phytophthora palmivora), which it spreads in its faeces. (Mead 1961; Muniappan et al. 1986).
The introduction of Achatina fulica has often lead to the purposeful introduction of predatory snails and flatworms as biological control agents. These agents usually have a devastating effect on the environment. For example, a particularly important cause of the demise of the endemic snails in forested habitats in Tahiti and Hawaii has been the deliberate introduction of the predatory snail (Euglandina rosea and predatory flatworms, such as Platydemus manokwari to control Achatina fulica. However, reports that this flatworm can control Achatina fulica remain correlative and are based on an insufficient understanding of ecological principles (Muniappan 1990).
Achatina fulica is a vector for several pathogens and parasites, including the roundworm responsible for eosinophilic meningo-encephalitis in humans (News from MAF 2005) and the bacterium Aeromonas hyfrophila (also found in shellfish in New Zealand) (Kliks and Palumbo 1992). The parasites carried by the snail are usually passed to humans through the consumption of raw or improperly cooked snails (Moore 2005). For example, in American Samoa 16 Korean fishermen contracted eosinophilic radiculomyeloencephalitis disease following eating a meal of Achatina fulica infected with the parasite Angiostrongylus cantonensis (Kliks et al. 1982).
Achatina fulica are also a general nuisance when found near human habitations and can be hazardous to drivers, causing cars to skid. Their decaying bodies also release a bad stench and the calcium carbonate in their shells neutralises acid soils, altering soil properties and the types of plants that can grow in the soil (Mead 1961). Uses
Achatina fulica has been introduced purposely and accidentally to many parts of the world for medicinal purposes as well as for food and for research purposes. It has economic importance as a medicinal and protein source (Muniappan 1990). Geographical range
Native range: Achatina fulica is native to East Africa (Moore 2005).
Known introduced range: Achatina fulica has been introduced into most regions of the humid tropics, including many Pacific islands, eastern and southern Asia, and the Caribbean (Moore 2005). Introduction pathways to new locations
Agriculture: Accidental with agricultural products (probably eggs and small snails).
Aircraft: Accidentally associated with commerce.
For ornamental purposes:
Horticulture:
Ignorant possession: Accidentally associated with personal belongings.
Landscape/fauna "improvement": Introduced deliberately as a novelty pet or as a novelty faunal addition.
Live food trade: Smuggled as a food resource.
Military: Accidentally associated with military maneouvers.
Nursery trade: Accidentally associated with plants and soil (small individuals and eggs, most probably).
Other: Targeting risk industries such as nurseries, farmers markets, vehicle depots is important to prevent long distance spread of the snail.
Pet/aquarium trade:
Road vehicles (long distance): May get attached to vehicles unobserved.
Seafreight (container/bulk): There is a huge risk of the giant African snail (Achatina fulica) being spread and introduced into new locations via trade routes. It is frequently moved with agricultural products, equipment, cargo and plant or soil matter. The snails ability to store sperm is a distinct advantage and could enable a founding population to form from just one individual.
Smuggling: For use as food, medicinal use, or ornamental.
Translocation of machinery/equipment:
Transportation of habitat material:
Local dispersal methods
Escape from confinement:
Garden escape/garden waste: Eggs and snails readily transported in garden waste.
Horticulture (local):
Natural dispersal (local): Individual snails may travel up to 50 meters overnight (Mead 1979, Secretariat of the Pacific Community 1999). However, in New Caledonia the snails were found to move an average of 250m per year (Tillier 1981). 125m per month (particularly in wet weather) should be taken into account for natural dispersal.
Translocation of machinery/equipment (local): May get attached to machinery (e.g., road construction, landscaping) unobserved.
Transportation of habitat material (local): Movement of plants, soil, garden rubbish, building materials, vehicles and equipment should be inspected to contain the snail in a localised area. Management information
Molluscs are one of the most intractable of pests once established. As there is a risk of Achatina fulica being spread via trade routes there is potential to prevent its spread via international quarantine and surveillance activities. The snail has been intercepted widely by quarantine officials (Moore 2005), including in "empty" containers on a vessel travelling from Pagopago, American Samoa, to New Zealand. This was despite certificates indicating they were free of Achatina fulica (News from MAF 2005).
Initial invasions of A. fulica have been eradicated from a few locations, notably Florida (USA) and Queensland (Australia). Control costs can range from $US60,000 dollars for a 7-month procedure, to over $US700,000 dollars for the eradication in Florida (Muniappan et al. 1986, Smith and Fowler 2003). Attempts to eradicate Achatina fulica in Queensland (Australia) and in three states in the USA have all involved hand collection of animals, followed by subsequent destruction (Mead 1979). However, the most pragmatic approach to control of terrestrial molluscs is the use of pesticides. Please see section 2.1.3 of Barker and Watts (2002) for comprehensive information on the application of pesticides (molluscicides) to control of terrestrial mollusc pests. Nutrition
Achatina fulica has a remarkably broad range of host plants on which it feeds. Young snails with shell heights of 5mm to 30mm are most predacious on living vegetation, with very small and older individuals preferring detritus and decaying vegetation. The major requirement of hatchlings is calcium until their shell reaches the 5mm size (Mead 1961, Mead 1979). Young A. fulica appear to prefer soft textured banana (Musa), bean (Beta vulgaris) and marigold (Tagetes patula). As the snail matures its dietary preferences broaden to include a larger variety of plants, including brinjal (Solanum melongena), cabbage and cauliflower (Brassica oleracea v. capitata and botrytis), lady’s finger (Abelmoschus esculentus), sponge gourd (Luffa cylindrica), pumpkin (Cucurbita pepo), papaya (Carica papaya), cucumber (Cucumis sativus) and peas (Pisum sativum) (Raut and Ghara 1989). Reproduction
Achatina fulica is an obligate-outcrossing hermaphrodite, which means that one externally fertilised snail can establish a population (Smith and Fowler 2003). . A. fulica produces large eggs that are 4.5mm to 5.5mm in diameter and only hatch at temperatures above 15°C (Srivastava et al. 1985). Snails begin laying eggs at six months of age and fecundity lasts approximately 400 days (Smith and Fowler 2003). Snails lay up to 100 eggs in their first year, and up to 500 in their second year; fecundity declines after the second year, but snails may live up to five years with a total egg clutch of up to 1 000 (Raut and Barker 2002). Lifecycle stages
Eggs hatch in anything from a few hours to 17 days. Snails mature at around 5 to 15 months, depending on the temperature (with cold winter temperatures inducing hibernation and delaying sexual maturity). Achatina fulica lifespan can be up to 9 years, with 5-6 years being the norm (Mead 1961) (Raut and Barker 2002). This species has been nominated as among 100 of the "World's Worst" invaders Reviewed by: Major update under progress
Dr. Robert H. Cowie, Center for Conservation Research and Training, University of Hawaii
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
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Last Modified: Thursday, 23 March 2006
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