The monsoons are here and apart from the now cyclic clutch of near-fatal fevers, parts of Kerala are now under attack from a most invasive pest, the Giant African snail. This brownish, affable-looking intruder which devours vegetation and multiplies exponentially was first noticed in some southern and northern districts in 2005. But now, in several panchayats in the southern district of Pathanamthitta, it’s eating up plants and vegetables and creeping up the walls of houses, feeding on the calcium content in lime and cement. Calcium enhances its shell. The species was reportedly brought to Calcutta from Mauritius as far back as in 1847. Later on, down the years it was noticed in Karnataka, Orissa and Bihar.
Now, it seems to have found an idyll in Konni, Pathanamthitta, where homestead crops have been devastated. Tackling the menace has not been easy since the snail is nocturnal. By morning it goes underground, leaving farmers aghast at the plunder. And it seems to reproduce at will, not at all at a snail’s pace. The number of eggs per clutch averages around 200. A snail lays 5-6 clutches a year with a survival rate of 90 per cent.
The problem in checking the growth of the giant snail (Achatina fulica), a native of East Africa, is that it’s a hermaphrodite (species with both male and female reproductive organs). Snails of the same size mate and transfer sperm mutually. Local photographer Ratheesh Babu noticed this first when his bike trampled some on the roads and he heard the sound of shells breaking. He took a few snails home to see whether they could be grown in captivity and could be set upon insects and parasites. “But one day I noticed that the jar was full with new offspring. That’s when I realised their capacity to multiply,” says Babu.
His two daughters did a bit of research and found that in a 40-square metre area near the local temple the snail population had increased from 800 to over 7,000 in 10 months. Adult snails can reach a height of around 7 cm and a length of 20 cm or more. Farmers spray a concoction of tobacco and copper sulphate to destroy them. Even common salt works. But too much salt in the soil ruins it. The agriculture department has been supplying metaldehyde as a pesticide but it only seems to kill native snails and slugs.
The African snail can’t stand heat and sunlight but nature has gifted it with some crucial survival techniques. It can go into a summer sleep (akin to hibernation) for over two years, retaining the body’s water content. Worse, it can store sperm for nearly three months. Which means a single snail that gets translocated from infested places can detach itself at a congenial distant area and establish a new colony. “The remedy lies in cordoning off infested areas and spraying the tobacco concoction on a war footing. Or else, it’ll spread all over, especially because it likes the monsoon and the swampy conditions of Kerala. It poses a grave threat to Kerala’s vegetation,” says Dr T.V. Sajeev of the Kerala Forest Research Institute, who is closely working with the Asia-Pacific Forest Invasive Species Network.
The locals in Pathanamthitta have also been complaining of an increase in ant attacks at homes following the snail outbreak. Ants come out in large numbers to feed on the snails and their colonies too swell. Another species which has welcomed the snail outbreak is the crow pheasant which seems to relish the new prey.
Environmentalists believe the snail’s rampant growth is a symptom of Kerala’s fragile environment, which has suffered a heavy casualty of molluscs and insects on account of the rampant use of pesticides in farms and paddy fields in past decades. It’s possible that this led to a decline in the numbers of their predators too. Devoid of competitors and predators, the African snail has found an opportunity to thrive.