It wouldn’t be entirely false to claim that the snail invasion Kerala battles every monsoon is, in part, a man-made menace.
The man responsible for this lived in Palakkad 25 years ago, and it was here that the state's population of the Giant African Snail began, recount researchers at the Kerala Forest Research Institute (KFRI).
“The snails had arrived in Kerala from Singapore for research purposes. But the researcher soon disposed them off as the project was mothballed due to personal reasons,” says TV Sajeev, principal scientist at KFRI.
However, back then, the Palakkad-based researcher was unaware that he had practically imported Frankenstein’s monster, which would go on to invade 85 percent of Kerala by 2019.
Scourge for locals
Early warnings were present as the first complaints from residents came within a few years of the snails arriving in Palakkad.
“The first snail invasion was traced near the Government Victoria college area in Palakkad. The snails reproduced aggressively and turned into a serious scourge for locals. To get rid of them, a program was started by the district administration where Rs 1 would be given in exchange for one snail. However, the snail population was so large that people collected dozens of them and the scheme had to be shelved for lack of funds,” Sajeev says.
Rated among the 100 most invasive species by International Union for Conservation of Nature (IUCN), the Giant African Snail or Achatina Fulica have already spread to 12 out of 14 districts in Kerala.
Barring Idukki and most of Wayanad, their populations have been recorded in every region. In Pathanamthitta, Ernakulam, Thiruvananthapuram and Muzhuppilangad and Parassinikadavu in Kannur, their populations have turned into an acute monsoon menace, forcing residents to vacate their homes in rare cases.
So acute was the problem that it forced Panchayats to approach the state government for a solution 7 to 8 years ago.
Local self government members from villages complained to the Agriculture Ministry first. However, there was no specific department for the snails and hence the ministry refused to help.
The Health Ministry also dismissed the issue as the snails were not found to spread any grave diseases. When Forest Department officials were sought, they too refused to work with the species. Finally, the KFRI took over and a team was set up to study the spread and eradication of these snails. Sajeev is part of this team which has been studying the snails for over five years now.
The team’s first assignment was to map the snail populations and their possible spread.
"Their populations were traced to 124 regions within Kerala and we also prepared a simulation model to map neighbouring regions that were easy targets for the invasions," Sajeev says.
In these snail-prone areas, KFRI sensitised local panchayats on eradication methods. In the early days, the Pathanamthitta health department urged residents to spray Metaldehyde, a chemical toxin that can kill the snails. However, this was soon shelved as the chemical killed aquatic life when it mixed with surrounding water bodies.
Soon enough, Metaldehyde was replaced by a mixture of copper sulphate and tobacco decoction, discovered by two research students who were studying snail eradication independently.
“We field tested the chemical mixture of copper sulphate and tobacco decoction and this proved to be highly successful,” Sajeev adds.
Not only was the newly-found chemical a neurotoxin, which killed the species, it also prevented bacteria from growing on dead snails, preventing decomposition.
In order to spray the toxin, researchers placed crushed papaya leaves as bait to attract snails in droves.
Decades of control measures later, today the KFRI has a nodal department which only focuses on invasive species of all kinds, including snails, and helps keep them in check.
Snails - an agricultural menace and health hazard
Despite sensitisation programmes, the South West and North East monsoons in Kerala still see the maximum levels of Giant African snail invasions. They enter kitchens, stick on compound walls for calcium and feed on 500 different plants including papaya, tapioca, colocasia, ginger and all tuber crops.
Research has also found that wild populations of the Giant African Snails carry Angiostrongylus cantonensis, a parasite which causes meningitis.
“If they enter the kitchens, this could lead to the parasite’s spread. We even advice people to use gloves while handling them,” Sajeev adds.
Trade helped spread snails
But it's not just Kerala. The Giant African snails, originally from Kenya and Tanzania, have found new homes in Tamil Nadu, Karnataka and the North East. Through trade and commercial activities, the species was able to cross oceans and spread over new lands. This is, in part, due to the import and and export of wood that boomed in the 1980s and helped distribute the gastropod.
In Kerala, this phenomenon was found in Willingdon Island in Ernakulam, which is a yard for imported timber. A molecular study of the the Giant African Snails from Willingdon Island revealed that they came from different parts of the world.
“They had varied genetic make up, although their features were the same. This helped reassert the theory that the snails spread with the wood,” Sajeev says.
Once they spread, the snail species, which can withstand a wide temperature range, look for moisture to breed and proliferate.
Mating and reproduction
Like most snails, the Giant African species too is hermaphroditic, with each snail having both male and female reproductive parts. This means that 100 percent of this snail population have reproductive capabilities.
And they reproduce with great vigour, helping their invasive nature, states Sajeev. Each individual snail can lay up to 500-900 eggs, twice a year.
“The snails have ‘mating ducts’ which fuse together to transfer the sperm into the female. Usually, the bigger snail assumes the role of the male and the smaller one, the female. If no other snails are found, an individual snail will self mate,” Sajeev adds.
The species typically engineer their mating season to coincide with the rains. Most eggs hatch into tiny snails during the wet months.
The eggs are buried under the soil and remain there until the next spell of rains when they turn into hatchlings. Greater moisture requirement forces the snails to crawl under the soil during the non-rainy months.
“When the rains are over they go back under the soil, tricking residents into thinking that the menace is over. Yet, the following rainy season, these snails are sure to return, much to the annoyance of people,” Sajeev adds.
An adult snail lives for 5-7 years and can start laying eggs within a year.