A swarm of stink bugs and a river of rats: why India’s flowering bamboo causes a crisis for humans

Every few decades mass blooming in Mizoram’s forests causes a rodent boom – and devastation to crops. The cycle is well-known, so why aren’t farmers and authorities better prepared?

In the hills of Mizoram state in north-east India, the first thing that farmers notice are the swarms of stink bugs, known locally as thangnang. It can mean only one thing: the rats are coming. And with them, famine.

As dawn breaks in Mamit district, Maunsanga, a 62-year-old farmer, walks across his plot, stopping where his rice crop once stood. He bends down to examine a broken stalk.

“I have been cultivating in this place for the last 40 years. Each year has had its own problems, but what I have noticed this year is that the damages are almost everywhere. No matter how alert we are even during night-time, there is nothing much that we can do about saving our crops,” he says.

The damage may be evident this morning, but it began months earlier, in late 2025, deep inside bamboo forests dominated by Melocanna baccifera and Bambusa tulda.

Each of these species flowers en masse once every few decades, producing huge numbers of seeds. These flowering periods go by different names: Melocanna baccifera’s is known as mautam, while Bambusa tulda’s is thingtam.

There is usually a gap of 18 years between a mautam and a thingtam, and 30 years between a thingtam and the next mautam. Once it begins, the mass flowering phenomenon is not limited to a single season, but can unfold over years – and is heralded by the thangnang bugs.

“The cycle usually happens every 48 to 50 years, depending on the bamboo species,” says Dr Lalthanzami, of the Forest Research Centre for Bamboo and Rattan.

“The seeds become a major food source for rodents. Their breeding increases rapidly during this period and once the bamboo seeds are depleted, the rodents spread into nearby farms,” he says.

Scientists say the crisis may have consequences beyond crop losses. After flowering, large stretches of bamboo die naturally, leaving hillsides more exposed during heavy rainfall seasons.

“Bamboo plays a major role in stabilising soil in these hill regions,” says Dr R Zoramthanga, of Pachhunga University College in Aizawl. “Once flowering is completed, the bamboo dries and dies. This increases the risk of soil erosion and slope instability, especially during monsoon months.”

He says heavy rodent feeding on bamboo seeds could also affect natural regeneration in some forest areas. Birds, insects and small mammals that depend on bamboo habitats are forced to adapt or move.

“It is not just a farming issue,” Zoramthanga says. “It is an ecosystem shift.”

In villages such as Hriphaw, Mamte and parts of Lunglei district, farmers say they first noticed unusual rodent activity late last year as bamboo flowering intensified in nearby forests.

Lalduhsaki, a farmer from Hriphaw, says at first he thought it was ordinary pest damage, but after some weeks he realised it was different. “The rats kept increasing and they were moving in large numbers.”

In Lunglei district, another farmer, C Lalhriliana, says families have spent weeks guarding fields at night.

“You hear movement in the grass before you see anything,” he says. “Sometimes there are so many that you cannot stop them. By morning, large sections of the fields are destroyed.”

According to estimates from the state agriculture department, more than 5,300 farmers have been affected across Mizoram. Rice has suffered the highest losses, though maize, ginger, pumpkin and beans have also been damaged. For many villagers, the damage to their harvest is already changing daily life.

“Earlier I could harvest 30 or 40 bags of rice,” Maunsanga says. “This year I got only three bags. It is not enough even for my own family.”

In Mamte, another farmer, Chungtea, says he tried changing planting schedules after hearing warnings from neighbouring villages.

“I planted early thinking we could avoid the worst period,” he says. “But the rats arrived before harvest. We lost almost everything.”

People in several districts say the effects are visible in local markets and ration shops, where subsidised grains are distributed by the government.

“We used to store food for months after harvest,” says Lalbiakzuali, from Aizawl district. “Now many families buy rice every week because they do not have enough stored grain.”

At some ration shops, queues have become longer in recent months as villagers increasingly depend on subsidised supplies.

The state government has started rodent control operations in affected areas, with agriculture department teams distributing chemicals including zinc phosphide and bromadiolone, alongside awareness campaigns on their use.

“We are trying to control the rodent population quickly before further crop losses happen,” says Hmangaihchhunga, a district agricultural officer in Lunglei. “Field teams are visiting villages regularly and monitoring affected areas.”

He says the government has started assessing crop losses for compensation and seed assistance programmes. Officials are also trying to reassure farmers that the rodenticides are safe, though concerns remain. In Hriphaw, a village council member, Vanlalruata, says some people refuse to use the chemicals because they fear contamination.

“Our water sources are very close to the fields,” he says. “People are worried that poison could enter streams used for drinking water and fishing.”

Instead, many communities have returned to traditional control methods. Bamboo traps known as vaithang and chepthang are now common along field edges and footpaths.

Farmers spend nights checking traps, carrying torches and trying to keep rodents away from crops. “We catch many rats every night,” Lalhriliana says. “Sometimes dozens. But the numbers are still very high.”

The thingtam cycle has been documented in Mizoram for generations. Records show similar rodent outbreaks linked to bamboo flowering, including during the 1958-60 famine, which had a lasting political and social impact on the region.

Prof Lalrinmawia, a historian at Mizoram University, says communities have long understood the pattern. “People know bamboo flowering can lead to rodent outbreaks,” he says. “But long-term planning and preparedness have remained inconsistent. Many times the response begins only after the damage has already started.”

Researchers say there is limited evidence on whether climate variability is affecting the intensity of ecological impacts linked to bamboo flowering. “The flowering itself is a natural biological cycle,” says Lalthanzami of the Forest Research Centre. “But changing rainfall patterns and environmental stress may influence how ecosystems respond.”

There have been calls for monitoring of the flowering of the bamboo, better storage facilities for grains, and alternative cropping systems. “We need preparation, instead of an emergency response every few decades,” Lalthanzami says.

For farmers, however, the immediate concern is surviving the coming months. “We need seeds for the next season,” Chungtea says. “People also need food support now.”

In Mamit district, as evening approaches, Maunsanga walks back from his damaged field carrying an empty sack.

“We know this will happen again,” he says. “But knowing is not enough. Each time, we start from the same place.”

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