India's Monkeys Keep Killing People, so Scientists Are Trying Radical New Sterilization Strategies

A monkey sits outside the Taj Mahal.
A monkey sits outside the Taj Mahal.
Photo: Julian Finney (Getty Images)

One evening last November, a young woman named Neha was feeding her infant son inside their house in Runkata, a small town in the outskirts of Agra, India. Suddenly, a monkey broke into the house, snatched the baby boy from her arms, and made away with him. Neighbors chased the unexpected kidnapper with stones, but to their horror, the baby was soon found lying blood-soaked on a nearby terrace. Despite being rushed to the hospital, Arush, who was just 12 days old, did not survive. Perhaps this sounds like a freak tragedy, a rare case of a wild animal behaving outside its natural order, but truthfully, there was nothing especially rare about this incident.


Less than a month before, in nearby Tikri, a 72-year-old man was stoned to death as he was scavenging for dry wood, when a troop of monkeys on the surrounding treetops rained bricks at him after picking them up from a nearby construction area. Elsewhere, in Himachal Pradesh, 86 cases of monkey attacks were registered with the state government from 2017 to 2018. In one strange incident, a monkey was spotted playfully showering fistfuls of cash at passing strangers from a treetop in Shimla, after picking up over ₹10,000 (around $140 USD) from a nearby home. Other incidents of hostile simians turning on humans have been reported across Tamil Nadu and Odisha.

There are a few reasons behind the sudden increase in aggression among the macaques of India, according to Iqbal Malik, a primatologist and environmental activist based in New Delhi. “The rhesus macaques, generally speaking, are a harmless and peaceful species. They live in troops, with each troop consisting of infants, sub-adults, sexually mature adults, and the elderly. Infants stay close to their mothers up to the age of six months, and the mother-infant bond is extremely strong,” Malik explained to Gizmodo by phone. “Reports of violence among rhesus macaques mostly emerge from cases of chaotic fissioning, breaking of groups, and separation of mothers and infants.”

Large-scale deforestation destroys their natural habitats, resulting in the fragmentation of groups and causing monkeys to move towards rural and urban areas in search of food, she said.

A monkey in Jammu, India.
A monkey in Jammu, India.
Photo: Channi Anand (AP)

Moreover, the rhesus macaque is an excellent forager, Sindhu Radhakrishna said in an interview with the Hindustan Times. Radhakrishna is the dean of the Animal Behavior and Cognition Programme at the National Institute of Advanced Studies, Bangalore. When monkeys infiltrate human habitations, they find easy access to energy-rich foods, which is why they like staying close to humans, she said.

In 2006, Himachal Pradesh became the first state in India to introduce surgical sterilization for rhesus monkeys, aimed at curbing their ever-increasing population and finding a possible solution to the rising reports of simian violence leading to agricultural damage throughout the region. As of 2019, there are about eight monkey sterilization centers spread across the state, where macaques brought in by trappers are sterilized using laser vasectomies in males and endoscopic thermocauteric tubectomies in females, Satish K. Gupta, emeritus scientist specializing in Reproductive Cell Biology at the National Institute of Immunology, New Delhi, said in an email to Gizmodo.


The results of the program, however, were inconclusive, Gupta said. While the number of rhesus macaques in the state reduced from 3.2 million in 2004 to 2.1 million in 2015, incidences of violence seem to have remained more or less the same.

Malik believes that the poor execution of the program may have had the unintended effect of making the monkeys more aggressive. “The sterilization itself is innocuous, if done right. However, the forest department’s haphazard approach to the trapping and release of monkeys and their treatment before and after the operation, could be the real reason behind the problem.” The rhesus macaques are a strongly tribal species, she said. When individual monkeys are trapped and separated from their tribes, it disrupts an intricate communal bond. This is especially pronounced in the case of young juveniles who make for easy catches as they are separated from their mothers. When the monkeys are reintroduced into the open, they find it difficult to fit in, causing them to look for alternate sources of food near human habitations. It also makes them violent and temperamental, Malik said.


Following after Himachal Pradesh, the Agra District Administration partnered with a local nonprofit called Wildlife SOS to run a similar program in Uttar Pradesh throughout 2016. However, only 500 monkeys had been captured by 2018, while the expenses incurred by the administration exceeded ₹18,600,000 (over $260,000 USD). As with Himachal Pradesh, the actual number of attacks involving monkeys showed no signs of slowing down, said Javed Akhtar, the chief conservator of forests with the government of Uttar Pradesh.

In response to repeated failures, the Indian government is now considering alternate means of population control for the macaques. Immunocontraception, a technique which involves the administration of a vaccine that creates a temporary immune response against a protein or hormone crucial to reproduction, therefore rendering the monkeys infertile, is receiving particular attention. However, there are quite a few caveats.


“The major issue here is the delivery of the vaccine,” said Gupta, who noted that current vaccines often require multiple injections throughout the year in order to have the desired effect. A proposed solution to this problem has been turning the vaccine into a consumable pill and placing it inside monkey bait, but even that presents multiple challenges, as the leader of a troop will consume most of the oral bait and only the leftovers will be available to other monkeys, Gupta said. Immunocontraception is a technique most feasible for larger animals, such as elephants, which can be targeted via dart guns, he explained. The Ministry of Environment has currently assigned its immunocontraception project to the Wildlife Institute of India.

Despite the considerable efforts put in by the government to study different methods of population control for the rhesus macaque, no real research has been done to understand the long-term effects of these birth control procedures on the monkeys and their biology, said Gupta. In the absence of a viable birth control strategy and the required know-how to execute it properly, the most helpful idea may be to encourage people to avoid feeding stray monkeys or leaving leftovers out in the open, said Malik. Not showing your teeth or making eye contact, making loud noises to scare away strays, and keeping trash bins and water tanks covered at all times are some other suggestions provided by the New Delhi forest department. Unfortunately, these tips likely provide little feeling of security to the people living in daily fear of these primates.


Ritoban Mukherjee is a freelance science journalist based out of West Bengal, India, who is curious about robots, dinosaurs, and everything in between. Twitter: @kosmodrone




Macaques are very intelligent creatures. Off the top of my head while teaching in Delhi:

- Macaque climbed to the 3rd story apartment of a neighbor. Climbed through the window. Went straight to the breadbox and stole rolls. Then, opened the fridge and took some veggies.

- Macaque troop climbed to the top of the roof of another neighbor and opened their water tank. The troop bathed in the tank and then left. Monkey poo in the drinking water.

- Macaque troop turned on the spigot and hose of another neighbor. Troop had some drinking water. But, they were not polite enough to turn off the water when they were done. Neighbor ran out of water.

- A family of Macaques used to have breakfast each morning outside my front door. Each day, I would wait for them to finish before I walked to work. However, one day I had to get to work early. So, I left early - during their breakfast. Once I walked outside, the troop scattered: moms grabbed their babies and ran up a telephone pole, elders climbed up a short wall, etc. However, the adolescent males were pissed. A couple of them grunted at me. Whereas one of the adolescents climbed down from a tree and stood up on his hind legs and literally threw a punch at me (mind you, he did not clench his fist - it was more like a slap). I was caught off guard and shrieked. The sound of me screeching frightened him and he ran up a wall. Other adolescent males had grunted at me as I have walked to school in the past, but this was the only time one actually confronted me.

-One way that the city tried to keep macaques away was to employ “Monkey Wallahs.” These men would ride their bikes with Langur monkeys on their handlebars. When the Macaques saw the much larger Langur in their neighborhood, they would flee (just would still regroup 30 minutes later). The best part of seeing the Monkey Wallah was during the cooler months. During that time, the monkey would be wearing an adorable hand-knitted sweater that was bright red.