Armies of snails are marching across the State, devouring crops, fouling water sources, crawling through houses and sending citizens into a tizzy.
Heavy infestation has been reported from Alappuzha and Pathanamthitta districts and pockets in Thiruvananthapuram since the onset of monsoon when conditions became favourable for the Giant African snail ( Achatina fulica ) to emerge from hibernation and proliferate. The slimy shelled creature is one among the worst invasive species in the world.
Studies conducted by the Kerala Forest Research Institute (KFRI), Peechi, indicate that the alien species is spreading to more places in the State. Scientists admit it is difficult to eradicate the menace.
According to T.V. Sajeev, entomologist at KFRI, A.fulica became an invasive species in Kerala because of the few predators, hermaphroditic (having both male and female reproductive organs) nature, high rate of reproduction, hibernation capability, and generalist feeding nature.
Threat to cropsA serious agricultural pest, the Giant African snail is known to attack more than 500 plant species, including vegetables, coconut, cocoa, papaya, banana, arecanut, coffee, and even rubber. Though there has been nothing so far to suggest that the snail could be a disease carrier, the fact that it is a vector of the nematode Angiostrongylus contonensis causing Eosinophilic meningitis in humans is a cause for concern.
In Kerala, an infestation of snails was first reported from Palakkad in the 1970s. The adult snails grow up to 20 cm in length and 250 gm in weight.
Salt as destroyer“Managing a snail infestation is difficult because it is sporadic and not easy to monitor,” says C. Nandakumar, entomologist at the College of Agriculture, Vellayani. He advocates collection and destruction as the best control strategy.
Farmers use wet gunny bags and papaya leaves as bait to collect the snails. They then sprinkle common salt which penetrates the permeable skin of the snail, dehydrating it to death.
Other methodsDr. Sajeev, however, feels that a decoction of tobacco and copper sulphate is more effective in snail control.
A modelling study carried out by the KFRI revealed that the typical bioclimatic conditions in the lowland and river valleys in the midlands of Kerala were conducive to the proliferation of the snail. The presence of the snail has been reported from all but four districts.