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         General Impact

    For a detailed account of the environmental impacts of A. fulica please read: Achatina fulica (Giant African Land Snail) Impacts Information. The information in this document is summarised below.

    Achatina fulica is considered one of the worst snail pests of tropic and subtropic regions. While their small size limits the quantity of plant material consumed per animal the aggregated nature of the infestations can lead to severe damage in infested plants (Raut & Barker 2002). The process of naturalisation may ameliorate the impacts of this invasive species. Mead (1979a) expressed the opinion that “...the phenomenon of decline in populations of Achatina fulica appears to be inevitable”.

    Agricultural: In tropical agriculture the cost of A. fulica is fourfold. First there is the loss of crop yield caused by herbivory. Secondly, damage may be caused by the spread of disease through the transmission of plant pathogens. Thirdly, there is the cost associated with the control of the pest and, finally, there are the opportunities lost with enforced changes in agricultural practice such as limiting crops to be grown in a region to those resistant to snail infestation (Raut & Barker 2002).
    For a list of “Economically important plants recorded as being subject to losses through damage by Achatina fulica Bowdich (Achatinidae) in regions outside of Africa” please see the full Impacts document. Irrespective of crop the seedling or nursery stage is the most vulnerable stage. In more mature plants the nature of the damage varies with the species, sometimes involving defoliation and in others involving damage to the stems, flowers or fruits (Raut & Barker 2002).

    Economic/Livelihoods: In the US state of Florida it has been estimated that A. fulica would have caused an annual loss of USD 11 million in 1969 if its population had not been controlled (USDA 1982). In India it attained serious pest status, particularly in 1946/1947, when it appeared in epidemic proportions in Orissa and caused severe damage to vegetable crops and rice paddies (Pallewatta et al. 2002).

    Disease Transmission: A. fulica distributes in its faeces spores of Phytophthora palmivora in Ghana; P. palmivora is the cause of black pod disease of cacao (Theobroma cacao); the oomycete which also infects black pepper, coconut, papaya and vanilla (Raut & Barker 2002). A. fulica spreads P. colocasiae in taro and P. parasitica in aubergine (Solanum melongena) and tangerine (Citrus reticulata) (Mead 1961 1979a, Turner 1964 1967, Muniappan 1983, Schotman 1989).

    Ecosystem Change:Costs to the natural environment may include (Raut & Barker 2002) herbivory; altered nutrient cycling associated with large volumes of plant material that pass through the achatinid gut; adverse effects on indigenous gastropods that may arise through competition; and indirect adverse effects on indigenous gastropods that may arise through control of the snail (eg: biological control with the rosy wolfsnail (Euglandina rosea) or use of chemical pesticides applied against achatinids.

    Human nuisance: A. fulica are also a general nuisance when found near human habitations and can be hazardous to drivers, causing cars to skid. Their decaying bodies release a bad odor 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).

    Human health: In many Asian, Pacific and American societies A. fulica may play a role in the transmission of the metastrongylus causative agents of eosinophilic meningoencephalitis (Angiostrongulus cantonensis and A. costaricensis).




         Location Specific Impacts:
    American Samoa English 
    Agricultural: In 1994 Achatina fulica threatened the production of basic food crops such as bananas and coconuts in Western Samoa. Damage to staple yam crops in the Samarai-Murua District were significant (Conservation International 2005, in Cooling 2005).
    Anguilla English 
    Agricultural: Achatina fulica is destroying cultivated plant life and other forms of vegetation in Anguilla. The snail spreads fungal and bacterial diseases of plants (Connor 2007).

    Economic/Livelihoods: The snails damage subsistence farmers’ crops. Residents continuously spend funds to control the snails. Some householders have resorted to procuring expensive poisoned bait to deal with the problem (Connor 2007).

    Human health: Achatina fulica is a potential carrier of the parasite Angiostrongylus cantonensis (rat lung worm), a potential cause of meningitis and brain damage, is associated with skin rashes (contact with slime) and the shells are potential breeding sites for mosquitoes (Connor 2007).

    Human nuisance: In some cases the snails leave unsightly trails on buildings and corrupt water sources around homes. They aggregate in large numbers becoming an unsightly nuisance and attach to houses leaving behind feces and slime. They overcrowd gardens and have the potential to create road blocks (Connor 2007).

    Reduction in native biodiversity: Achatina fulica has the potential to out compete other species of snails. It has been associated with destruction of native and endemic plants (Connor 2007).
    Brazil English 
    Agricultural: Achatina fulica occurs in dense populations in urban areas where it is a pest in ornamental gardens, vegetable gardens and small-scale agriculture. In rural regions A. fulica is present especially in vegetable gardens, small-scale plantations, or in abandoned agricultural areas, where the snails attack many crops to differing degrees (Thiengo et al. 2007). Those crop families most seriously affected in Brazil are the following: Acanthacea (Hemigraphis colorata, hera-roxa; Jacobinia coccinea), Araceae (Xanthosoma maffafa, boa), Asteraceae (Chicorium intybus, wild chicory; Lactuca sativa, lettuce), Cactaceae (Carica papaya, papaya), Compositae (Spilanthes acmella), Commelinaceae (Ipomoea batatas, sweet potato), Cruciferae (Brassica oleracea var. acephala, collard greens), (Brassica oleracea var. italica, broccoli; Brassica oleracea var. capitata, cabbage), Raphanus sativus, radish), Cucurbitacea (Cucurbita spp., pumpkin; Dioscorea bulbifera, yams), Euphorbiaceae (Lycopersicum esculentum, tomato; Manihot esculenta, cassava), Lamiaceae (Malpighia spp.), Malpighiaceae (Hybiscus spp.), Moraceae (Musa spp., banana), Musaceae (Ipomopsis spp.), Orchidacea (Arachis hipogaea peanut), Papilionaceae (Phaseolus vulgaris, bean), Rutaceae (Paulinia cupana, guarana), Sapotaceae (Capsicum annuum, bell pepper) and Umbelliferae (Boehmeria nivea) (Thiengo et al. 2007). Albuquerque and colleagues (2008) found A. fulica feeding on bull feces.

    Competition: Of concern is the damage caused to the environment, and potential competition with native terrestrial molluscs (Thiengo et al. 2007). Brasil has many large native snail species (eg: Megalobulimulus spp., Orthalicus spp., Thaumastus spp.) that superficially resemble A. fulica. These species may be vulnerable to competition with A. fulica, especially because they lay clutches of few eggs (Jurberg et al. 1988; Salgado Unpub., in Thiengo et al. 2007), whereas A. fulica lays clutches of up to 400 eggs (Raut and Barker 2002).

    Ecosystem change: Achatina fulica threatens wetland ecosystems in Pantanal. At some locations (chapadas and planaltos) A. fulica is a problem, but another invasive mollusc, Limnoperna fortunei (Bivalvia, Mytilidae) introduced from Asia is considered an even bigger problem in the wetland areas (C. Callil, pers. comm.).

    Human health: Many infections are spread by fresh water and terrestrial snails (Teles et al. 1997, Carvalho et al. 2003, in Albuquerque et al. 2008). Albuquerque and colleagues believe that A. fulica could represent a threat to human health and for this reason must be controlled or eradicated. The occurrence of A. fulica in new areas is particularly important to public health since it is one of the intermediate hosts of Angiostrongylus spp., a nematode that parasitises domestic animals and man causing an important emerging zoonosis (de Paiva Barcante et al. 2005). Thiengoa and colleagues (2008) provide the first report in Brazil of the development of A. abstrusus infective larvae in A. fulica evidencing the veterinary importance of this mollusc in the transmission of A. abstrusus to domestic cats. The mollusc is an important host for Angiostrongylus cantonensis, which occurs in Asia and the Pacific Islands and is a causative agent for eosinophilic meningoencephalitis (Graeff-Teixeira 2007). In the Americas there is another metastrongylid worm, A. costaricensis, that causes abdominal disease and may also be transmitted by A. fulica (Graeff-Teixeira 2007). Although both infections may occur in focal outbreaks and with low morbidity, very severe complicated clinical courses pose a challenge for diagnosis and treatment (Graeff-Teixeira 2007). However, data presented by Neuhauss and colleagues (2007) do not support a significant concern about the possibility of Angiostrongylus spp. transmission: parasitic burden and recovery rate of inocula in A. fulica were extremely low.

    Human nuisance: Populations of introduced Achatina fulica may reach enormous densities, to the extent that they crawl up the walls of houses in great numbers, make walking on sidewalks difficult without treading on them, and there have even been reports of cars skidding on massed crushed snails on roads (Mead 1961, in Thiengo et al. 2007).
    Cote d Ivoire (Ivory Coast) English 
    Agricultural: Within a short period of its introduction into the Ivory Coast Achatina fulica had achieved significance as a crop pest (von Stanislaus et al. 1987, in Raut and Barker 2002).

    Competition

    Economic/Livelihoods: At present there is little economic information on the economic status of Achatina fulica in areas invaded in Africa (Raut & Barker 2002). However, within a short period of its introduction to the Ivory Coast, A. fulica achieved dominance in the Achatinidae community (Raut & Barker 2002).
    Galapagos Islands (Ecuador) English 
    Reduction in native biodiversity: It has been estimated that more than a third of the endemic species of Orthalicidae in the Galapagos have become extinct during the last half century, in part due to the introduction of alien species (Coppois 1995, Parent & Smith 2006, in Borrero et al. 2009). From a conservation viewpoint, the presence of A. fulica in western Ecuador may be considered a major threat to "Darwin‘s Laboratory" (Borrero et al. 2009).
    French Polynesia English 
    Agricultural: In these islands Achatina fulica quickly became an agricultural pest.

    Competition: The impact of Achatina fulica on indigenous flora or gastropods is not documented locally, however, it may exclude indigenous snails (Meyer & Picot 2001).

    Herbivory: Achatina fulica may pose a threat to native plants (Meyer & Picot 2001).
    Ghana English 
    Agricultural: Within a short period of its introduction into Ghana A. fulica had achieved significance as a crop pest (von Stanislaus et al. 1987, in Raut and Barker 2002).

    Competition: Achatina fulica entirely displaced a native snail in Ghana (Cooling 2005).

    Disease transmission: Achatina fulica distributes, in its faeces, spores of Phytophthora palmivora, the cause of black pod disease in cacao (Theobroma cacao) plants in Ghana (Evans 1973, in Raut and Barker 2002).

    Economic/Livelihoods: At present there is little economic information on the economic status of Achatina fulica in areas invaded in Africa (Raut & Barker 2002). However, within a short period of its introduction into Ghana A. fulica achieved dominance in the Achatinidae community (Raut & Barker 2002).
    Guam English 
    Agricultural: Irrespective of crop the seedling or nursery stage is the most preferred stage and the most vulnerable. In some situations infestations of crops in the seedling stage are so severe as to demand changes in the crop species cultivated. In Guam, Indonesia and Malaysia, for example, A. fulica infestations made it uneconomic to grow vegetables, at least during the period of peak infestations (South 1926, Kondo 1950a, Mead 1961, in Raut & Barker 2002). Thus production of some crops has proved unsustainable in certain infested areas.
    India English 
    Agricultural: Irrespective of crop the seedling or nursery stage is the most preferred stage and the most vulnerable. In some situations infestations of crops in the seedling stage are so severe as to demand changes in the crop species cultivated. In India, for example, A. fulica infestations made it uneconomic to grow papaya (Carica papaya) (Raut & Ghose 1984, in Raut & Barker 2002). Thus production of some crops has proved unsustainable in certain infested areas. In the Inida (Raut & Ghose 1984, in Raut & Barker 2002) it has also proven difficult to produce yam due to A. fulica infestations.

    Economic/Livelihoods: Infestations of Achatina fulica have caused sufficient damage to crops to render growing of some vegetables unviable.
    Andaman and Nicobar Islands (India) English 
    Agricultural: This pest is polyphagous, attacking about 225 plants of agricultural and horticultural importance, including cuttings and seedlings. Vegetables belonging to the families Cruciferae, Cucurbitaceae and Leguminoseae are known to suffer the most damage. A. fulica is considered a serious pest of nursery beds of vegetables and flower plants. The snails move out of hideouts at dusk and feed throughout the night ravaging the seedlings (Prasad et al. 2004).
    Indonesia English 
    Agricultural: Irrespective of crop the seedling or nursery stage is the most preferred stage and the most vulnerable. In some situations infestations of crops in the seedling stage are so severe as to demand changes in the crop species cultivated. In Guam, Indonesia and Malaysia, for example, A. fulica infestations made it uneconomic to grow vegetables, at least during the period of peak infestations (South 1926, Kondo 1950a, Mead 1961, in Raut & Barker 2002). Thus production of some crops has proved unsustainable in certain infested areas.
    Japan English 
    Reduction in native biodiversity: More than 100 species of land molluscs have been recorded on the islands, of which 94% are endemic (Tomiyama & Kurozumi, 1992, Tomiyama 1994, in Ohbayashi et al. 2007). However, about 40% of the endemic species are already extinct (Kurozumi 1988, Tomiyama & Kurozumi 1992, in Ohbayashi et al. 2007). The following may be possible reasons for this decline:
    • Introduction of exotic snails such as A. fulica (Kurozumi 1988, Tomiyama 2002a, in Ohbayashi et al. 2007);
    • Introduction of the predatory snail E. rosea for the control of A. fulica in 1965 in Chichijima Island (Takeuchi et al. 1991, in Ohbayashi et al. 2007);
    • Predation by predatory flatworms distributed before P. manokwari invasion (Kawakatsu et al. 1999; Okochi et al. 2004, in Ohbayashi et al. 2007);
    • Invasion of the alien predatory flatworm P. manokwari in Chichijima Island in the 1990’s (Kawakatsu et al. 1999, Tomiyama 2002a, Ohbayashi et al. 2005, in Ohbayashi et al. 2007);
    • Predation by alien rats (Tomiyama 2002a, in Ohbayashi et al. 2007); and
    • Forest destruction (Tomiyama 2002a, in Ohbayashi et al. 2007).
    Madagascar English 
    Agricultural: It has assumed pest status through damage to crops (Barker 2002). It potentially feeds on a range of crops.

    Predation: Introduction of putatative biocontrol agents for A. fulica may lead to predation on non-target species (secondary or indirect impact).
    Malaysia English 
    Agricultural: Irrespective of crop the seedling or nursery stage is the most preferred stage and the most vulnerable. In some situations infestations of crops in the seedling stage are so severe as to demand changes in the crop species cultivated. In Guam, Indonesia and Malaysia, for example, A. fulica infestations made it uneconomic to grow vegetables, at least during the period of peak infestations (South 1926, Kondo 1950a, Mead 1961, in Raut & Barker 2002). Thus production of some crops has proved unsustainable in certain infested areas.

    Human nuisance: Achatina fulica is considered a serious garden pest in Malaysia.
    Mauritius English 
    Human nuisance: Achatina fulica is considered a serious garden pest in this country.
    Ile aux Aigrettes (Mauritius) English 
    Competition: Achatina fulica. may compete with some of the snail species selected for reintroduction: Ile aux Aigrettes once had a rich snail fauna but now hosts only relatively common species (Dulloo et al. 1997, Griffiths Cook & Wells 1996, in Craze & Mauremootoo 2002).

    Reduction in native biodiversity: Achatina fulica is present in large numbers as an invasive species and is a threat to the continued existence of the native flora (Mead 1979, in Craze & Mauremootoo 2002).
    Nepal English 
    Agricultural: Achatina fulica is a serious pest of vegetables and considered to be a major problem in kitchen home gardens by District Agriculture Officers in many districts where they occur. Many farmers have complained that they could not grow nursery-raised vegetables by transplanting them into the fields because they are immediately eaten by A. fulica. They can completely wipe out vegetable crops such as cauliflower, potato, cabbage, pumpkin, cucumber, bottle gourd, white gourd, spinach, radish and tomato. Cereals such as hyacinth bean, cow pea, black gram, maize and millet, and fruits such as banana, guava, papaya, and jack fruit are all considered to be vulnerable. One of the respondents in Mirmi told us that one day they destroyed 500 recently transplanted cauliflower and cabbage plants within just one night (Budha & Naggs 2008).

    Human nuisance: The snail is reported to leave sticky slime trails and excreta wherever it goes, including on vegetable leaves and the walls of houses. The density of rotting snails can impart an offensive odour along extensive lengths of road.
    New Zealand English 
    Agricultural: A. fulica could impact horticulture, agriculture, forestry and home gardens in New Zealand. Of the more than 500 species of plants it feeds on, the following plants are found in New Zealand: bananas (Musa spp.), Asplenium spp., Bougainvillea spp., cabbage and Cruciferae, cactus (Opuntia and Cereus spp.), Canna spp., carrots, capsicums, Compositae, Tagetes spp., Citrus spp., Cucurbitacea, Daphlia spp., eucalyptus spp., ferns, figs, hibiscus, Impatiens balsamina, jasmine, Leguminosae, lettuce, lilies, oleander, orchids, passionfruit species, potato, Rosa species, spinach, Solanaceae (egg plant, chillies and tomato), taro species, tabacco and yam (Raut and Barker 2002; Mead 1961, Srivastava 1992, Animal and Plant Health Inspection Service 2005, in Cooling 2005).

    Economic/Livelihoods: New Zealand's horticultural exports increased from approximately $1 300 000 in 1997 to approximately $1 800 000 in 2000 (Statistics New Zealand 2004, in Cooling 2005) and this sector would be one of the most likely, along with the nursery industry to be affected.

    Other: The snail has the potential to out-compete and displace native species, to alter the community composition, to modify the habitat and to introduce fungi and parasites into native ecosystems.

    Reduction in native biodiversity: Achatina fulica is known to eat Asplenium, Phorium and Cordyline snails (Venette & Larson 2004, in Cooling 2005). There are 16 native Asplenium species in New Zealand (Dawson and Lucus 2000, in Cooling 2005). A. fulica is also likely to cause significant harm to native plants (Animal and Plant Inspection Service 2005, in Cooling 2005).
    Northern Mariana Islands English 
    Agricultural: Irrespective of crop the seedling or nursery stage is the most preferred stage and the most vulnerable. In some situations infestations of crops in the seedling stage are so severe as to demand changes in the crop species cultivated. In Mariana Islands, for example, A. fulica infestations made it uneconomic to grow watermelon (Citrullus lanatus) and papaya (Carica papaya) (Chamberlin 1952, Raut & Ghose 1984, in Raut & Barker 2002). Thus production of some crops has proved unsustainable in certain infested areas.
    Rota Is. (Northern Mariana Islands) English 
    Agricultural: In Rota Island (Kondo 1952, in Raut & Barker 2002) it has proven difficult to produce yam due to A. fulica infestations.
    Saipan Is. (Northern Mariana Islands) English 
    Agricultural: In Saipan Island (Lange 1950, in Raut & Barker 2002) it has proven difficult to produce yam due to A. fulica infestations.
    Papua New Guinea English 
    Agricultural: A. fulica has been observed feeding on Taro in Papua New Guinea. Extensive damage to taro leaves has been seen at Situm Lae, Morobe Province and in Wewak, East Sepik Province. It feeds on the leaves, leaving behind the leaf vein (N. Simbiken pers. comm. 2006).
    Philippines English 
    Agricultural: In the Philippines (Pangga 1949, in Raut & Barker 2002) it has proven difficult to produce yam due to A. fulica infestations.
    Singapore English 
    Human nuisance: The snail is considered a serious garden pest in this country.
    Sri Lanka English 
    Agricultural: In Sri Lanka (Green 1910b, in Raut & Barker 2002) it has proven difficult to produce yam due to A. fulica infestations.
    Taiwan English 
    Agricultural: Achatina fulica has caused significant damage to vegetable crops and citrus in Taiwan.

    Human nuisance: Achatina fulica is considered a serious garden pest in Taiwan.
    Thailand English 
    Human nuisance: The snail is considered a serious garden pest in Thailand.
    Trinidad and Tobago English 
    Agricultural: Onions, potatoes, sunflowers, eucalyptus, brassicas and lettuce are preferred by A. fulica (Government of Trinidad and Tobago 2005, in Cooling 2005).
    Lana`i (Lanai) Is. (United States (USA)) English 
    Competition: Achatina fulica is causing the local extinction of unique snails.
    United States (USA) English 
    Agricultural: Mead (1961, in Venette & Larson 2004) lists four categories of plants that are likely to be damaged by A. fulica. The first category is garden flowers and ornamentals, which are completely susceptible at any stage of development. The second category is mostly vegetables with a higher probability of damage to Cruciferae, Cucurbitaceae and Leguminosae. The third category represents plants usually not eaten at the mature stage but are damaged earlier in development by bark being completely removed as is the case with breadfruit, cassava and teakwood. The final category includes crops upon which damage is indirectly incurred (e.g. when snails destroy a preceding cover crop) (Mead 1961, Muniappan et al. 1986, in Venette & Larson 2004).

    Threat to endangered species: Threatened and endangered plants in the US are potential hosts for A. fulica (Venette & Larson 2004).
    Hawaii (United States (USA)) English 
    Reduction in native biodiversity: Individuals of Achatina fulica were observed preying on veronicellid slugs at two sites on the island of Oahu, Hawaii. As such, the presence of A. fulica may pose a greater threat to terrestrial mollusc conservation than previously imagined.
    Venezuela English 
    Agricultural: The giant African snail is considered an agricultural pest.

    Disease transmission: A. fulica is a vector of parasitic worms in humans.



ISSG Landcare Research NBII IUCN University of Auckland