Sniffer dogs: hot on the trail with the pet detectives

Dogs are used to detect everything from drugs to landmines, but the science behind the sniffers is surprisingly thin

A sniffer dog searches for mines along the border between Syria and Jordan. Photograph: Salah Malkawi/Getty Images

A sniffer dog searches for mines along the border between Syria and Jordan. Photograph: Salah Malkawi/Getty Images


As Rosslare Europort opens at 6am, Ralph is straining to get to work. His job is to locate cash, heroin, amphetamines, marijuana and other narcotics. He will put in a long shift for what seems a pittance. When he found more than €1 million worth of heroin last summer, he sat and waited for this reward: a tennis ball.

Last month, he helped uncover 4.5kg of herbal cannabis with a street value of €90,000. Ralph is an English springer spaniel, a detection dog for the Revenue. His most important traits are a desire to work and an obsession with the ball.

Dogs like this are used to detect everything from drugs to landmines, yet the science behind sniffers is surprisingly thin. The United States invested heavily in technology after the September 2001 terrorist attacks but came to realise that a ball-obsessed dog and his nose still wins.

Dogs don’t handle or eyeball objects, and so they take a good sniff, concentrating molecules in their nose. Their nose lining is rich in receptors; while we have about six million, a sheepdog boasts 200 million receptor cells. This would allow a dog to detect a teaspoon of sugar diluted in two Olympic- sized swimming pools.

Working dogs such as labradors and spaniels are favoured, but more breeds are being recruited. There isn’t much evidence to say one breed is better than another; what is certain is that a top sniffer dog is more than a good nose or the right breed.

A certain temperament
Sniffer dog trainers say it takes a certain temperament for a dog to become a star detector – and a clue to what it takes is that, often, top sniffer dogs start out as unwanted pets.

Ralph at Rosslare was one such dog. He was sent off to the Blue Cross in England. Fortunately, someone there saw potential in the unwanted spaniel and phoned Wagtail, a dog-training company.

“The dogs we need are highly motivated and very independent and fearless. They are usually what people might call naughty dogs,” says Louise Wilson, a lead trainer at Wagtail in Wales. “These dogs are relentless, and will continue to bring you the tennis ball for hours on end.”

Denny Lawlor, Ralph’s handler in Wexford, says: “It’s the drive in him. You would know it to look at him.”

When Ralph arrived he was suffering from malnutrition and his coat and skin were in incredibly poor condition. “From Ralph’s outlook and personality you wouldn’t know it,” says Helen Evans, his trainer at Wagtail. “Ralph was always an excitable, bouncy but sweet-natured dog. He excelled in his training and is still one of the quickest dogs I ever trained.”

A rare breed
Just three or four dogs in a thousand in the pet population might have what it takes. One trainer in the US tours rescue centres looking for ball or tug-toy obsessed dogs. His best detector is a Chihuahua.

Why a dog would work hard for a mere ball might seem puzzling to us, but the ball signals an event – fun and interaction with its owner. “Some dogs are highly motivated by the game that the tennis ball indicates,” says Dr Alexandra Horowitz, a behavioural scientist and author of the book Inside of a Dog . “They might like holding the ball in their mouths and to play a game with their handler.”

Dogs have also evolved to become expert people-watchers, as Horowitz writes: “Dogs are anthropologists amongst us. They are students of behaviour, watching us in a way that the science of anthropology teaches its practitioners to look at humans.”

Even pets are geniuses at body language. Pick up your keys to go out and an ear pricks up. They can be cued toward an object by bowing or nodding, or the turn of a head. After some training, they can find an object just by our eye movements.

“Dogs are attuned to our gestures, especially ones we habitually do,” says Horowitz. This is a problem for dog trainers; they must guard against cheating canines.

“Sometimes the dropping of your own shoulder when in training, because you see the item, could make the dog indicate [a find] ,” Wilson says. Pros often film themselves during training so that they are not inadvertently giving the game away in a poker-like “tell” that can be read by the dog.

What chemicals Ralph uses to spot old or new money or heroin in a hidden compartment isn’t known. What is certain is that a dog’s nose is not easily hoodwinked. “People try everything to distract dogs, such as placing food or coffee among drugs,” Lawlor says. Wilson says she has found chillies being used, but to no avail.

Today, Irish Revenue deploys 14 sniffer dogs – mainly labradors and springers – to detect drugs, cash and tobacco. Handlers practise their trade with significant success, while scientists still grapple with how they do it.

At Florida University, Dr Clive Wynne says the scientific evidence is amazingly thin, especially given the size of the sniffer industry and the fact that people rely on dogs to locate landmines. None of this bothers Ralph or his handler; they demonstrate an understanding between our two species formed over thousands of years.


A dog’s nose is so remarkable that we are still finding new uses for it. Dog trainer Louise Wilson at Wagtail, which trains dogs for Irish Customs among others, says dogs could potentially be trained to detect illegally smuggled rhino horn.

Everything has an odour, including illegally traded animal parts. Wilson has already helped to train and supply Gabon with dogs to detect illegally smuggled African elephants, and she believes dogs can help against illegal smuggling of endangered animals in other countries.

Dogs have also been shown in recent years to be capable of detecting human cancers.

The first reports came out in the medical literature in 1989, when a young woman in the UK told her dermatologist that her dog had been nipping and barking persistently at a suspicious mole on her leg.

Work towards an “electronic nose” for cancer detection has been going on for decades, but the dogs are still miles ahead.

Two recent reports in the European Respiratory Journal showed that dogs were able to distinguish between the breath of lung cancer patients and those without lung cancer. Researchers speculate that a “pet” scan could be used as an initial screening tool. In one study, dogs identified 71 samples with lung cancer out of a possible 100.

In Britain, the charity Medical Detection Dogs says that all dogs and breeds have the capability to detect cancer in humans. The charity says its dogs can detect minute odours associated with many cancers, although it is not known what exactly they are sensing.

Neither the Irish Cancer Society nor the HSE uses sniffer dogs for cancer detection, but say they would welcome further research.

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