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INVASIVE ALIEN SPECIES


FAUNA

For a small island, Sri Lanka is rich in biological diversity. Yet, this natural wealth is under threat from various sources, including invasive alien species.
IAS grow rapidly, compete vigorously, push out native species and alter ecosystems. Their impacts are enormous and they have the potential to cause damage to the environment, human health, livelihoods and the economy.
Currently, 8 species of animals.
 
 
 
 

Giant African Snail

Lissachatina fulica (Férussac, 1821)

Common names: Giant African Snail (English): Kalutara Golubella (Sinhala)

Synonyms: Achatina fulica (Bowdich, 1822), formerly Férussac, 1821Gient Snail

Identification characters:

Lissachatina fulica has a narrow, conical shell, which is twice as long as it is width. The shell is generally reddish-brown in colour with weak yellowish vertical markings, but coloration varies with environmental conditions and diet. A light coffee colour is common (Cooling, 2005). A fully grown snail consists of 7-9 whorls (10 in some exceptional cases) with a moderately swollen body-whorl and a sharply conical spire, which is distinctly narrowed but scarcely drawn out at the apex.

Total length:

Adults of the species may exceed 20 cm in shell length but generally average about 5-10 cm. The average weight of the snail is approximately 32 g (Cooling, 2005).

History of introduction:

This species was first introduced to Sri Lanka in the 1900s. Available records suggest that this species was not introduced deliberately but through the negligence of a British planter.

Present distribution:

This species is seen to be native to the coastal region of East Africa and is also seen to occur in large numbers along the forest margins (Crowley & Pain, 1964 in Raut & Barker, 2002). Lissachatina fulica appears to extend its range from 250-830 km from the coast, travelling further inland in the northern section of the range (Mead, 1949, J. Bequaert in Lange, 1950, in Raut & Barker, 2002).

In Sri Lanka, it appears to have an island wide distribution. They are inhabitants of mainly agricultural/horticultural lands and may extend into lowland rain forests.

Dispersal and reproduction:

These snails usually start laying eggs at 6 months of age and their fecundity lasts approximately 400 days. This species is known to be an obligate-crossing hermaphrodite: one externally fertilized snail could establish a population (Smith & Fowler, 2003). Lissachatina fulica is known to lay large eggs with diameters ranging from 4.5 to 5.5 mm. Their eggs are only known to hatch at temperatures above 15oC (Srivastava et al., 1985).

Individual snails have been seen to travel up to approximately 50 meters overnight (Mead, 1979; Secretariat of the pacific community, 1999). However, the natural dispersal rate should be considered as 125 meters per month (particularly in wet weather).

The spread of the species may facilitated by the transport of eggs or adults as passive passengers when moving plants, soil, garden waste, vehicles, building material and equipment from infected areas to new locatities.

Impact on native species and habitats:

The possible effects of Lissachatina fulica on natural habitats and native species are not well documened. They may have a direct effect on both terrestrial vegetation and native snails, either by feeding or functioning as competitors respectively. It is listed as an agricultural pest.

Direct exploitation/ destruction of native species:

Direct exploitation of native species by Lissachatina fulica is not known. But, it may have a significant impact on the native plants, and native snails as discussed above.

Current uses: No uses are documented.

Natural threats (predators): Common coucal and Mongoose are the main predators of Lissachatina fulica.

Prevention and control: Poor quarantine regulations and the animal's high reproductive capacity are the main reasons for the rapid dispersal of this snail. Preventing its introduction is the most cost effective option. Because of the huge risk that the Giant African Snail (GAS) poses as well as its multiple methods of dispersal, strict quarantine and surveillance activities are necessary to control its spread. Creating awareness about the various negative impacts of the snail can help stop the illegal import of GAS for trade and its international spread.

Control: Control methods like collecting snails by hand or incinerating them with flame throwers have been used to control infestations of GAS, but neither of these methods are very effective. In China, the snail is used as a food item, which controls the population to a large extent, but may also encourage further deliberate spread. Chemical control involves using Metaldehyde, Methiocarb or a combination of these chemicals with other molluscicides as bait formulations or foliar sprays. But these chemicals can also harm non-target snails and endemic forms. In India, cuttings of Anona glabra are used as a snail repellent to protect nursery beds. Kerosene and salt are used in some countries to control the snail. The predatory rosy wolf snail (Euglandina roseai), which is native to the southeastern United States, has been introduced to islands in the Caribbean, Pacific and Indian Oceans as a biological control agent for the GAS. However, in Hawaii and French Polynesia, this predatory snail has caused the extinction of numerous endemic tree snails. Platydemus manokwari, a turbellarian flat worm, has been reported to be successful in controlling GAS in Guam, Philippines and Maldives. However, this worm has also been implicated in the decline of native snails.

1243Drowingmap

 
 
IAS Documentary
Information for the public knowledge about Invasive Alien Species in Sri Lanka...

AS policy Intro
Information about the policies of Invasive Alien Species in Sri Lanka...



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