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These highly trained rats have sniffed out 150,000 explosives

The rats are fine: How once-overlooked animal skills are helping humans

By Molly Callahan

Every weekday, as the sun comes up over Morogoro, Tanzania, an elite team of land mine-detection specialists begins its training. While the breeze blows through the grassy, 60-acre training ground, the specialists weigh in (to ensure their carefully calibrated diets are on track), then set to work searching for deactivated, buried land mines. 

They have been trained since birth for this vital work. And for every land mine they find, during training and in the field, they’re rewarded with a delectable mash of bananas and avocados, or maybe a few peanuts. 

The specialists are rats. Gambian pouched rats, to be exact. The organization they work for, APOPO, has trained hundreds of them to sniff out and signal the location of buried land mines.

And they’re ideal for the job. Weighing about three pounds — roughly the size of a three-month-old kitten — they’re light enough not to set off the explosives. Their superb sense of smell enables them to detect the presence of as little as a billionth of a gram of explosive material. Indigenous to the sub-Saharan region where they work, they’re efficient breeders, with a gestation period of about a month. They’re highly intelligent and exacting, but also fun to work with — congenial, outgoing, curious.

Through the end of 2021, the rats have been responsible for finding 150,000 explosives, including land mines, that were then safely deactivated and removed from the ground. Across seven countries in Africa and Southeast Asia, they’ve had a hand (or paw) in returning 70 million square meters of land back to communities that need it, and “freed close to 2 million people from the terror of land mines,” says Lily Shallom, APOPO’s communications manager.

For centuries, humans have employed other members of the animal kingdom to perform duties that perfectly match their innate skills. Shepherds use dogs to corral flocks of sheep; farmers release goats to eat encroaching poison ivy; British officials have long kept cats in government buildings to protect against mice. This last practice can be traced back to the 1500s, and in 2011 the British prime minister’s feline-in-residence, Larry, was bestowed with an appropriate, if cheeky, title: Chief Mouser to the Cabinet Office.)

More recently, however, humans have turned to animal species beyond those usual suspects — for jobs that perhaps come less intuitively to those new animal partners. The US Navy, for example, trains dolphins to detect underwater explosives in its Marine Mammal Program. 

“If you look at the tree of life, there is such a diversity of attributes that non-human animals can bring to humans,” says Jennifer Smith, an evolutionary biologist at Mills College at Northeastern University. Dogs and cats have been domesticated over time to fill specific needs for humans, but many other animals can also be helpful, she says.

In other words, a dog may be a man’s best friend, but humans have been busy making other friends, too. 

When it comes to choosing those friends, Smith considers an animal’s umwelt, a German word that animal behaviorists use to describe the world as each organism perceives it. Though we all may share the same environment, humans perceive that environment differently than bats, which perceive it differently than rats. 

Humans, for example, have excellent vision — but only during the day. At night, a bat’s high-pitched screams can help it echolocate small moths from nine yards away in total darkness. An owl’s dish of stiff feathers around its face funnels sound to its sensitive ears so that it, too, can track prey at night.

Might the unique strengths of each animal, developed over millennia for a specific purpose, be harnessed to fill in the gaps in humans’ abilities?  

Animals “can offer attributes to humans, or the possibility for partnerships where other species can do things differently, or add value to the lives of humans,” Smith says. 

As anyone who’s tried to train a cat knows, though, a good partnership relies upon more than just dovetailing abilities. 

Magawa died from natural causes a few months after his eighth birthday. He found over 100 landmines and other explosives during his career in Cambodia, making him APOPO’s most effective rat to date.

“When I’m thinking about animals as partners, I’m also thinking about their longevity, for example,” Smith says. Golden retrievers are highly trainable and make for excellent service animals. But their lifespans, relative to their human counterparts, are short. By the time a retriever is trained to recognize its handler’s low blood sugar or help its visually impaired partner navigate the city, the dog only has a few years left.

“We’re talking about living animals that have their own needs and their own lives,” Smith says. “I think it can be a win-win if both the human and non-human are getting something out of it” — through, say, protection from predators or a reliable source of food. 

When we do find the right partnership, she notes, animals can help untangle some of the most vexing problems humans face. And the results can be lifesaving.

Land mines are one such problem. Buried during decades-old conflicts, the subterranean explosives still injure or kill thousands of people per year. The Land Mine and Cluster Munition Monitor, an independent watchdog group, estimates that millions of land mines are still buried around the world, with a particularly high concentration in southern Africa left over from colonial and post-colonial wars. Between 1961 and 1997, leftover land mines claimed the lives of 250,000 people in the region, according to a 1997 report by Human Rights Watch

That year, 133 countries signed on to the Anti-Personnel Mine Ban Treaty, an international agreement facilitated by the United Nations that bans the production and use of land mines. As diplomats were meeting in Ottawa to codify the treaty, another idea was born a continent away that would also help to save lives. 

Bart Weetjens, then a graduate student in product design at the University of Antwerp, was considering the problem of land mines from a different angle. A Zen Buddhist monk and entrepreneur, Weetjens kept rats as pets. He knew they were intelligent animals with superior scent-detection abilities — capabilities that would make them perfect for finding buried land mines.

Weetjens and a friend — Christophe Cox, now APOPO’s chief executive — teamed up in 1995 on a rat research project. Weetjens had come across some research touting gerbils’ scent-detection abilities, and he wondered whether rats, which were cheaper, more widespread across the world, and more intelligent than gerbils, could do the same thing.

That research would eventually grow into APOPO, named for a Dutch acronym that translates to “Anti-Personnel Land Mines Removal Product Development” in English. The organization, founded in Belgium with an operational headquarters in Tanzania, now sends trained rats to known land mine sites around the world. Weetjens and APOPO have been recognized for humanitarian work by organizations such as the World Economic Forum, Ashoka, and the Skoll Foundation.

APOPO is currently active in Angola, Zimbabwe, Mozambique, and Cambodia; it has completed mine-detection missions in Vietnam, Laos, and Thailand. It has also provided mine-detecting dogs to projects in South Sudan and Turkey.

APOPO’s trainers use a positive-reinforcement method to train the rats from a young age to sniff out inactive TNT, gradually making it harder and harder to find as the pups grow up. Naturally curious and highly motivated by food, the rats are eager to explore their surroundings for the buried TNT (which the trainers pack into tea infusers), knowing that they’ll be rewarded for their discovery with a treat from their trainer, says Shallom, the APOPO spokesperson.

Over about a year, the rats are trained to find smaller quantities of explosive material within larger plots of land. They run through training exercises until they detect 100 percent of the loaded tea infusers, and then must pass a test in which they’re allowed only one false positive. Once they graduate, the rats can be deployed throughout southern Africa and southeast Asia, where they’ll sniff out land mines until they retire, Shallom says. 

A single APOPO rat can have a sizable impact. In January, the organization mourned the loss of Magawa, who died from natural causes a few months after his eighth birthday. Stationed in Cambodia, Magawa found over 100 land mines and other explosives during his career, making him APOPO’s most effective rat to date, Shallom says. 

In recognition of his valor, the People’s Dispensary for Sick Animals, a charity organization, awarded Magawa its gold medal — the organization’s highest honor, akin to the George Cross award given out by the British government for “acts of the greatest heroism or of the most conspicuous courage in circumstances of extreme danger.”

Magawa’s line of work is, indeed, highly dangerous — for humans. Pressure-activated antipersonnel land mines typically require about 11 pounds of weight to detonate. This makes them a terrible threat even for children skipping across mine-infested territory. 

But the rats are too small to set off a mine. Indeed, not a single APOPO-trained rat has died in the line of duty, Shallom says. Ensuring the rats’ well-being throughout their entire lives is an important part of APOPO’s mission, she says. “We really do think of them as our partners.”

The rats are kept in clean kennels with their siblings as young pups and are moved to their own enclosures as adults, Shallom says. They’re fed a balanced diet and enjoy frequent play breaks, even during training. A veterinarian visits the site every other week to check on their health. And, when older rats start to become less enthusiastic in the morning — a sign that they’re ready for retirement — they’re transferred out of the workforce. At that point, the rats still receive regular health checks and stimulating playtime for the remainder of their lives, six to eight years on average, Shallom says. “We have had a few retirees who hit the ripe old age of 10,” she says.

Land mine detection is just the beginning for APOPO, Shallom says. The organization has also trained rats to sniff out tuberculosis in samples of sputum — a mix of saliva and mucus coughed up from the lungs. So far, they’ve screened more than 800,000 samples and found an additional 25,000 tuberculosis patients that local clinics missed, she says. The organization is also exploring whether the rats can be trained to find survivors in collapsed buildings or other catastrophes. 

The possibilities for human-animal partnerships may be limited only by our imagination. Consider the glowworms that helped British troops read maps at night during World War I, or the ferret-engineer who helped the US military connect new computers to its missile warning center in 1999. Perhaps there are some tasks for which other animals are simply more qualified than humans.  

“In terms of animals, it’s just trying to come up with innovative ways to use their skills,” Shallom says. “Rats have this amazing sense of smell; how can we use that in scenarios that would be difficult for a human? Often it comes down to getting past the barriers we’ve already set in our minds about how we view or think about these animals. Rats get a bad rap, but they’re really spectacular little guys.”

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Molly Callahan is a senior writer for Boston University.

Photo by APOPO


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