They may be pests in a house, but in a war zone, these rats can be lifesavers.
Trained rats can sniff out TNT in landmines.
The rodents are trained through Pavlovian conditioning: a click sound to signal a food reward whenever they make the correct detection.
It takes nine months of hard work before a rat is deployed for mine detection.
A baby rat in a tiny red and black harness twitches its pointed nose incessantly, probing a grassy field where it is being trained by a pioneering Dutch NGO to smell out deadly landmines.
Other rats trained under the same scheme have already helped clear large swathes of land in neighboring mine-infested Mozambique.
Babette, the two-month-old baby, walks unsteadily across the weedy patch followed by two trainers rolling a bar that teaches her to go back and forth across the patch in straight lines.
Light, with an acute sense of smell and easily motivated by food rewards, giant African pouched rats have been found to be highly effective in mine detection by APOPO, the Dutch non-governmental organisation that launched the training project -- the first of its kind -- in this Tanzanian town.
The rodents are trained to detect the TNT in landmines through Pavlovian conditioning: a click sound to signal a food reward whenever they make the correct detection.
Training begins at four weeks old when the baby rats are exposed to humans to rid them of their fear of people and new surroundings, after which they are taught to associate a click sound with food.
Once that is achieved, they are then trained to distinguish TNT scent from other smells. When they successfully distinguish it, the click is sounded and they are given a bit of banana, thus reinforcing the link between positive TNT identification and food.
In all, it takes nine months of painstaking on- and off-field training for a rat to be deployed for mine detection.
"This work is not easy," recounts trainer Abdullah Mchomvu, holding a rat cage under his left arm. "You have to be patient. Sometimes I get frustrated, but then again I tell myself these are animals."
But "this work saves lives," he added.
It takes two de-miners a day to clear a 200 square-meter (2,150 square-feet) minefield, but if they work with two rats they can sweep it in two hours.
"Detection is the most difficult, dangerous and expensive part of mine action. Since rats are much easier to train than dogs, rats in this environment are much more appropriate," said Bart Weetjens, the founder of APOPO.
"They are very effective. We have very high success rates. So far they have helped re-open almost two million square meters (21.5 million square feet) of land" in Mozambique.
Despite their contribution, rats are more often seen as vermin that spread disease and destroy harvests.
"Rats absolutely have an image problem. People don't like them and that is one of our biggest struggles," said Weetjens. "We are trying to change that perception. Rats are very sociable, very intelligent highly likable creatures."
APOPO calls its sniffers "hero rats" in recognition of the work they perform.
The organization's website pictures rats that could be straight out of Beatrix Potter: all pink noses and quivering whiskers.
APOPO has even launched an Adopt-a-Rat scheme where individuals and corporations can contribute to the upkeep and the training of a sniffer rat, receiving in exchange an adoption certificate and email updates on the animal's training or career.
Weetjens said the next frontier would be to use the "hero rats" to sniff out narcotics or to search for survivors of disasters such as earthquakes or collapsed buildings.
