**4. Impact of snails on agriculture**

Many researchers have reviewed the impacts of invasive mollusks on agriculture [42, 43] bio‐ diversity and human health. However, the annual costs associated with damage to the envi‐ ronment and agriculture due to alien species in the USA have been recently estimated to be US\$120 billion. The combined costs associated with damage for the United States, the United Kingdom, Australia, South Africa, India and Brazil have been estimated as US\$314 billion per year [43]. In the tropics, the loss caused by the snails is threefold. Primarily, there is loss of the agricultural products followed by the cost of labor and materials associated with the manage‐ ment of such pests. Lastly, there is opportunity losses related to the changes in agricultural practice such as cultivation of pest‐resistant species only.

Among mollusks, the giant African land snail, *A. fulica* tops the list of agricultural pests. *A. fulica* (*Lissachatina fulica*) is a herbivore, feeding primarily on vascular plants [21] and plant tissues containing high protein and calcium content [44, 45]. All *Achatinidae* species need cal‐ cium for the formation of shell and reproduction. Thus, environments rich in calcium carbon‐ ate, such as limestone landscapes having a pH of 7.0–8.0, and urban areas with abundant concrete are preferred [28].

The adult snail of *A. fulica* daily consumes large quantity of plant material approximately 10% of its weight [46]. The seedling stage of plants is most preferred and vulnerable. The extent of damage is based on the chemical composition of the plant and varies spatially as well as temporarily [47]. Many researchers have stated that infestations by snails to the nursery stage are so severe that demands change in cultivation practice. For example, in Malaysia, Guam and Indonesia, during the season of peak infestations of *A. fulica*, it is almost impossible to grow vegetables [27, 48, 49].

*A. fulica* is considered the most damaging land snail in the world as it can dwell on over 500 different crop species. It is a non‐host specific pest of crops like peanuts, beans, peas, cucumbers and melons. If fruits and vegetables are not available, snails can feed on variety of ornamental plants, tree barks and even paint on houses [21]. The snail also allies with other soil invertebrates to decompose the leaf litter [50] and is the most destructive pest; it is ranked second among the 100 worst alien invasive species [51]. It affects tropical and subtropical areas, causing large damages to farms, commercial plantations and domestic gardens. It can also be found on trees, decaying materials and next to garbage deposits [17]. In urban areas, the deposition of solid waste by humans is primarily responsible for the proliferation of pests [12]. This species has attained pest status also due to its voracious feeding, competing for physical space with the native fauna resulting in disequilibrium of biodiversity [12]. Apart from being an agricultural nuisance, snails can thrive in cities, crawl up the walls of buildings and skid cars on highways [27].
