Meet the giant rats fighting wildlife trafficking

MOROGORO, Tanzania — Often dismissed as pests, rats have long been misunderstood. But the African giant pouched rat (Cricetomys gambianus), the world’s longest, is challenging that perception. With its intelligence and super sense of smell, this species has captured the interest of scientists in Tanzania, who now plan to use it as a crime fighter against illegally trafficked wildlife parts.

This story starts in the 1990s, when industrial engineer Bart Weetjens was looking for viable technologies to detect landmines in countries in the Global South. He then had a thought: Why not use rats? They’re cheap, possess remarkable olfactory systems, and are social and intelligent animals, contrary to popular belief. And so Weetjens founded APOPO, a nonprofit rat training organization in Tanzania, home to the largest and longest-living rat species.

Some of the African giant pouched rats trained by APOPO can live up to a decade, while typical domestic rats typically live only two to four years. This longer lifespan, along with their exceptional sense of smell, has made the African giant pouched rat of invaluable service for many years in various projects. Previous generations of these giant rats have successfully assisted in landmine detection, which was Weetjens’s initial goal, and in detecting tuberculosis.

Now, the rats have been trained for a new project, focusing on tackling the illegal wildlife trade. In its final trial stages, trainers have worked with the first cohort of wildlife detection rats.

How to train a giant rat

“You really have to learn the rat you are working with,” says Dora Hebert, a trainer at APOPO. “Rats are different from one another. Just like human beings.”

Hebert has worked for APOPO since 2022, focusing on the wildlife detection project. She, along with a group of scientists and trainers, is working to prepare eight rats to uncover all sorts of illegal wildlife products in cargo shipments, such as pangolin scales, rhino horns and elephant ivory.

These giant rats are bred in captivity, but they’re also occasionally crossbred with wild individuals. Selected rats begin training at a very young age, but not all will be suited for the job. Trainers look for individuals that are social, confident and eager to search for targets. Rats that fail to bond with their trainers or show little interest in the work are retired to a designated area for inactive rats. Only those that respond well to early interactions move on to formal training.

They’re trained in two key skills using positive reinforcement. When the rats are just a few months old, Hebert says, the trainers start teaching them to recognize the scent of target items, such as landmines, tuberculosis or wildlife products, depending on the project, and distinguish them from other odors, even when masked by strong smells. At the same time, they’re also trained to communicate their findings.

All trained rats wear a harness equipped with a ball on their chest. When they detect a target, they signal their trainer by pulling the ball, which triggers a sound to indicate their discovery. When they correctly identify a target, they receive a reward.

“Usually a syringe filled with a mixture of avocado, banana and pellets,” Hebert says.

When the rats have mastered these skills, the organization deploys them to search for scents in hangars, boxes, containers and ventilation systems. Their training occurs in a facility replicating real-world working environments, such as airports and ports.

Catch me if you can

“When we look at exit points from East Africa, seaports play a significant role [in wildlife trafficking]. And that includes ports like Dar es Salaam,” says Mikala Lauridsen, program office director at the East Africa office of TRAFFIC, a global wildlife trade monitoring NGO. The idea is that the rats will help conquer the problem at target sites.

“Illegal wildlife trafficking is a global issue. You have many different trade routes, both within the country but also across the region and across the continent. And these trade routes change constantly,” Lauridsen says. “So wildlife trafficking is a tricky area to tackle.”

The illegal wildlife trade is worth up to $20 billion per year globally, according to Interpol.

“The main challenge as far as being able to detect illegal wildlife products is that the criminal gangs are getting so creative with the way that they’re moving illegal wildlife products,” Lauridsen says. It’s a classic cat-and-mouse chase for authorities and traffickers — so why not let a rat outsmart the mouse?

Although they sound like the perfect heroes, these giant rats also have their limitations.

“Tools and technologies are extremely important, but it’s the people on the ground, the enforcement agencies working together within countries and across borders, and having strong laws and policies in place that will make and create the effective change,” Lauridsen says.

And, of course, not everybody is ready to include a rat in their lives.

“I do not like rats,” Lauridsen admits, but then adds, referring to the APOPO project, “These are special rats. It’s amazing what they’re able to do. Equip[ping] enforcement officers with the right tools and technology is one of the best solutions we have.”

Promising results

The training of the first wildlife detection rats is still ongoing, but the early results are promising. The project, which started six years ago, has made significant progress, with different generations of rats validating various stages along the way. Last year, the team published its preliminary findings in Frontiers in Conservation Science, demonstrating that giant rats can be trained to detect commonly trafficked wildlife items in a controlled laboratory setting. Now, the latest generation, which has been in training for two years, appears to be the first one to be deployed on the ground.

“We are now near the 90% accuracy of these rats detecting the wildlife products,” says José Eduardo Reynoso Cruz, behavioral researcher and lead scientist of the wildlife detection project at APOPO. The goal is to exceed 90% certainty and, above all, to reduce false positives, which isn’t an easy task.

Handling samples, whether wildlife products or nontarget items, requires great care to prevent odor contamination. For instance, if a trainer’s scent transfers to a sample, the rat may associate the odor with the trainer rather than the sample, undermining the training. To prevent this, it’s crucial to follow methods that minimize contamination. Additionally, it’s important to introduce a variety of smells to avoid unwanted odors and ensure the desired scent is strongly imprinted on the animal.

“We need to continue our training to see if our rats are still capable of being more precise and work in other environments,” Reynoso says. With this goal in mind, the team is now conducting its onsite trials at Dar es Salaam’s airport and port.

“We try to approach now to a situation that is more similar to what the rats could be facing when they are deployed, and train our rats as best as we can, to try to achieve this goal by 2025,” Reynoso says.

As the illegal wildlife trade continues to evolve, the use of giant rats may emerge as an unexpected, yet effective, solution. Only time will tell, but for now, these unlikely heroes are ready to take on the challenge — one scent at a time.

Banner image: Dora rewards Nandera with a mixture of avocado, banana and pellets. Image by Lucia Torres/Mongabay.