Return of the Aliens? Giant African Snails Invade Balmatta Area in City & Destroy Vegetation & also Pose Threat to Humans
Mangaluru: While I am referring to them as Aliens, they are not from Mars or any outer planet, these Aliens are from the earth itself. They are the Giant African Snails that have invaded again. Giant African Snail (Achatina Fulica) is one of the world’s largest and most damaging land snail pests. The Global Invasive Species Database has included this snail among the “100 World’s Worst” invaders.. Something strange is seen in the neighbourhood of Shanthi Nilaya Hall/ KACES in the Balmatta area in the City, where hundreds of giant size African Snails are clinging to the walls and trees. They’ve spread far and wide and multiplied in numbers beyond belief in this vast Balmatta area. It is learnt that inadequate monsoon-related cleaning works owing to the Covid-induced lockdown has intensified the menace of giant African snails in this area. The snails have become a nuisance for residents forcing them to approach agriculture officials seeking remedial measures to eradicate the pest.
Sources reveal that these snails attack vegetation/plants and also pose a threat to human beings. The snails enter houses through drains and their secretions of cause itching and allergy. A nematode, which will cause eosinophilic meningitis, is carried by the African snails. These snails are non-host specific and can consume at least 500 different types of plants. Cereals, most vegetables – including tomato, chilis, beans, eggplant, cucumber, cabbage, and other vegetables- fruits and ornamental plants – are all vulnerable for attack by these foraging molluscs. Vegetables are easier to nibble on as they are softer. They also damage plantation crops such as coffee, areca nut, rubber, vanilla, and pepper, even coconut by feeding on seedlings or buds.
These snails impact habitats by devouring native plants and competing with indigenous snail species. Giant African Snail is a threat to the sustainability of crop systems and native ecosystems has a negative impact on native fauna and acts as a vector of human diseases. Giant African Snail is a macro phytophagous herbivore and it also eats sand, very small stones, bones from carcasses and concrete as sources of calcium. It is a threat to native snails and affects native ecosystems by altering the food chain by providing alternative food sources for predators. This voracious snail feeds on a variety of vegetables and is considered to be a major agricultural pest; it also attacks plantations of teak, rubber, coffee and tea. It causes severe damage to horticultural and medicinal plants. In most parts of the world, the damage is greatest when the species is first established.
Unutilized lands, like FACT compounds and various other places, have turned out to be the breeding grounds for snails, which can survive for up to six to seven years in ideal conditions. If no food is available, the snails survive by eating calcium from concrete particles on boundary walls. If moisture is not available in the atmosphere, it goes into hibernation until a favourable situation emerges. It can survive in hibernation for up to two years without food. Natural enemies for the giant African snail are few. Pigs and ducks are their predators. It is learnt that these snails are also imported as a food source. Other pathways of spread include moving snail infested soil, plants and agricultural products. The snail is consumed as food and also used for medicinal and research purposes. It contributes to the degradation of animal matter.
Though people use salt to kill the snails, experts suggest either using tobacco decoction or collecting the snails together and pouring salt over them since the shells of snails are rich in calcium. A botany professor from St Aloysius College said, “One should attract the snails first before using the tobacco decoction. First, land has to be dug in places where the menace is high. A gunny bag, soaked with fermented coconut water or beer or leaves of cabbage and papaya, should be placed in the pit. Since these snails are calcium-rich, they get attracted to it. When they come to eat it, tobacco decoction mixed with copper sulphate should be sprayed over the snails, and the pests will die in three to four minutes”.
The fully grown Giant African Snail consists of 7 to 9 (very exceptionally 10) whorls, with a moderately swollen body-whorl and a sharply conical spire, which is distinctly narrowed but scarcely drawn out at the apex. The snail can reach up to 20 cm in length and up to 12 cm in diameter. The normal lifespan of the Giant African Snail is 3-5 years, but some may live as long as 9 years. The snail reaches sexual maturity in less than a year. Giant African Snail is capable of aestivating for up to 3 years in times of extreme drought. Since this Balmatta area is filled with decayed vegetation and rotten tree branches/plants has given scope for these snails to multiply. The snail also thrives in forest edges, modified forest, and plantation habitats. It is active at night and in most cases spends the day buried underground. Giant African Snail is highly adaptable to dry and cooler climates and hibernates 10 to 15 cm deep in soft soil during less favourable conditions for up to one year.
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 Giant African Snail poses and also 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 Giant African Snail for trade and its international spread. The locations of hiding places and snails are to be destroyed. Hand collection and destruction will be effective during the early phase of infestation. Cut pieces of papaya stems may be placed for attracting and trapping the snails. Use wet gunny bags and papaya leaves as bait to collect and destroy them. Common salt may also be spread on the snail infested area. Predatory snails, hermit crabs, certain birds and millipedes are found to feed on this snail and check the increasing population. The research found a method of first attracting the snails with vegetable waste and then a point application of TDCS (Tobacco Decoction and Copper Sulphate) mixture to destroy the snails pretty effectively.
If a concentrated effort is not taken across affected areas, the invasion of these alien Giant African snails will continue and it will spell disaster for both vegetation/agriculture as well as local biodiversity.