Giant African Snail

In Solomon Islands

The giant African snail (GAS), Lissachatina fulica, previously known as Achtinidia fulica, arrived in Solomon Islands was first reported at Ranadi, Honiara, in 2006. It is believed to have arrived in the country several months earlier on earth-moving or logging equipment that had been landed without biosecurity clearance. Since then active campaigns have been carried out to, first, try to eradicate it but after that proved impossible, to reduce its impact and contain it to the outbreak area. Public awareness campaigns have been implemented and speedy responses made to eliminate all newly reported incursions. To date it is only confirmed to be established in Honiara and eastwards along the North coast of Guadalcanal.

Damage

GAS causes economic damage to a wide range of crops and ornamentals, vegetable crops are severely affected. Homeowners and market gardeners are all impacted and the Ministry of Agriculture and Livestock has been assisting by supplying snail baits to all requesting them. Recently the flatworm generalised snail predator Platydemus manokwari has been found in the area and it is reported as having a significant beneficial effect on the GAS populations. It is not known if the flatworm is indigenous or a recent introduction but this is the first reported identification in Solomon Islands. Attempts will be made to enhance the effects of the flat worm and spread it to new areas.

Usually, the snail eats rotten vegetation and animal wastes; however, a wide range of vegetables, ornamentals and tree crops are also eaten.   GAS attacks more than 500 types of plants, but it prefers breadfruit, cassava, cocoa, papaya, peanut, rubber and most species of legumes and cucurbits. Cuttings and seedlings are especially vulnerable. Damage is greatest when outbreaks first occur in a new area. Population explosions result in hundreds of snails per square metre. 

The economic impact of the snail is unclear. When first introduced, populations soar, but population explosions are often followed by population crashes. It then becomes a minor pest of agriculture and human health.

The rat lungworm parasitises the snail, and if the snails are not cooked thoroughly before being eaten by human beings, the lungworm can cause meningitis. 

Management 

Natural enemies - Ducks will attack the snail; they are the only type of livestock that will do so. Although population explosions can be immensely destructive immediately after spread to a new area, invariably snail population will decline. The problem is how to deal with the snail until that happens, which may be months or years.  Elsewhere predatory snails, such as Euglandina rosea and Gonaxis quadrilateralis have been introduced to control the snail, but the effects have been a disaster for local snail populations. Environmental impact studies are essential because of the non-specific nature of these predators.  As mentioned above the predaceous flatworm, Platydemus manokwari, is present in Solomon Islands.

Cultural control - The following are recommended:  

• Make a strip of bare earth about 1.5 m wide around cultivated areas. Bands of sand are also effective
• Collect snails regularly, preferably by mobilising the community – schools in particular. Bury the snails or feed them to pigs after boiling for an hour
• Conduct awareness campaigns:
  • Snails should not be kept as pets;
  • They are a threat to human health; and
  • Community action is needed to control them. 

Chemical control - Chemical control needs to be combined with cultural methods to be effective. The chemicals metaldehyde or methiocarb (as pellets containing 1.5-1.8 % of poison) are probably effective in small-scale cultivation, but their use over large areas is not encouraged. Take care to prevent livestock, pets and children from eating the pellets, put them in tins or bamboos in the evening and collect them in the morning. Poisoned snails should never be fed to pigs or other livestock.