Hundreds of people who live in seven villages in the southern Indian state of Tamil Nadu say they are reeling from an infestation of yellow crazy ants.
These insects, they say, attack their livestock and affect crop yields, putting their livelihoods in danger.
Yellow crazy ants are among the world’s worst invasive species, according to the International Union for Conservation of Nature.
They don’t bite or sting but spray formic acid, which can cause reactions.
These ants – their scientific name is Anoplolepis gracilipes – are usually found in tropical and sub tropical regions. They move in an erratic, uncoordinated way, with their movement becoming more frantic when disturbed.
Experts say these ants proliferate quickly and can “do a large amount of damage to native wildlife”. Many parts of Australia have reported infestations of these insects.
Dr Pronoy Baidya, an entomologist who has done research on yellow crazy ants, says they are an “opportunistic species”.
“They don’t have any diet preferences. They eat anything and everything,” he says, adding that they also prey on other ant species, bees and wasps.
The affected villages in Tamil Nadu are situated in a hilly region around the Karanthamalai forest in Dindigul district. Most people here are farmers or cattle owners.
“As soon as we go near the forest, the ants climb on us, causing irritation and blisters. We can’t even carry water to drink as they swarm that too. We don’t know what to do,” says Selvam, a 55-year-old farmer.
The villagers told BBC Tamil that they have seen these ants in the forest over the past few years. But this is the first time they have appeared in such large numbers in the villages, throwing life out of gear.
Cattle herders who lived near the forest say they have vacated their settlements due to the infestation.
“Since my house was infested with these ants, I left and came [to the village]. We are not able to control them, their numbers keep increasing,” says Nagammal, whose goats were attacked by the ants.
Local forest officer Prabhu told BBC Tamil that he has ordered officials to “conduct a thorough survey and submit a report”.
“I can comment on this only after getting the report,” he said.
Dr Singamuthu, a government veterinary doctor, told BBC Tamil that the ants “look like normal ants”.
“We do not know why they have spread. We also do not understand how to control them. We cannot say with certainty that this is the reason for the problems faced by humans and cattle,” he says, adding that villagers have been asked not to send their cattle into the forest for grazing.
Villagers, meanwhile, have alleged that their livestock and even snakes and rabbits have died after being attacked by these ants.
Dr Baidya said that the formic acid sprayed by hundreds of ants may have affected the eyes of the animals, but adds that “it is not recorded whether they specifically target the eyes”. In humans, he says the acid can cause allergic reactions but may not be life-threatening.
Experts are worried that proliferation of these insects could affect the ecology of the region.
When these ants first invaded Australia’s Christmas Island, they displaced native ants by attacking them and taking over their food sources, Dr Baidya says. They have also killed millions of red crabs on the island by blinding and incapacitating them.
Dr Priyadarshan Dharmarajan, an entomologist who works with a conservation group, says these ants have a symbiotic relationship with aphids, which are sap-sucking insects that can harm crops.
“They feed on the milk-like substance produced by aphids, which are not good for crops,” he says.
Dr Dharmarajan says the problem may have worsened now due to steadily rising temperatures.
“When the environmental temperature increases, their metabolic rate also increases, causing them to eat more. That could be a reason,” he says, adding that this can’t be confirmed without data.
“We have to collect more data regarding weather patterns in the areas of infestation and analyse it.”
