Can Bloodhound Dogs Smell Benzodiazepines?

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If ever a dog looked at home beside Sherlock Holmes' heel, it is the Bloodhound. That wrinkled face with droopy features and long, dangly ears immediately summons up images of a Bloodhound, nose down to the ground following a scent trail with a sleuth in tweeds following on behind. 

Indeed, such is the Bloodhound's reputation for picking up scents that they could be the poster-dog for sniffer dogs. But is a Bloodhound's scenting abilities limited to natural trails left by people or animals? Or can they detect substances such as drugs, of which benzodiazepines are an example?

The answer is a most definite "Yes" - Bloodhounds can smell benzodiazepines, and here's why. 

Introduction of Can Bloodhound Dogs Smell Benzodiazepines?

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Signs a Bloodhound has Smelled Benzodiazepines

Bloodhounds have the ability to smell a great many substances, indeed, the trick is to harness this ability to track down one particular odor. If we make the assumption that the dog has been trained to detect benzodiazepines, you can expect to see certain body language signals that show they are actively following a trail. 

When first directed to smell for drugs, the Bloodhound will scent the air. To do this, they move their head from side to side, nose high, in order to take small samples of air. The movement helps them work out where the concentration of scent molecules is strongest, and then move toward it. 

Whilst still distant from the source of the odor, the dog moves quickly. They either follow a zig-zag path or move their nose from side to side to constantly sample the air and stay on target. As part of this, the dog takes lots of rapid, shallow sniffs so as to constantly update the 'database' of signals coming back to them. 

Once close to the source of the odor, the dog switches to a different type of sniffing. This involves taking fewer, but deeper breaths. This focusses the nose on the quality (rather than quantity) of the smell. When the smell is natural, this gives the dog information such as how fresh the trail is. When locating drugs, it helps the dog pinpoint their exact location. 

Body Language

A Bloodhound on a scent trail shows certain body language traits. Those to be alert for include:
  • Alert
  • Barking
  • Whining
  • Pacing
  • Sniffing
  • Tail up

Other Signs

Other, more specific clues the dog is on a trail include:
  • Rapid, shallow sniffs or slow, deep sniffs
  • Nose to the ground
  • Taking a zig-zag route

A History of Bloodhounds

History of Can Bloodhound Dogs Smell Benzodiazepines?
The Bloodhound is an old breed with origins dating back to Europe in the third century AD. Two similar strains of Bloodhound developed almost in parallel. One strain, the St Hubert's Hound, was larger and tan or black colored. The other strain was white, of lighter build, and known as the Southern Hound. It was the St Hubert's Hound that went on to become the Bloodhound we recognize today, whilst it's thought (but not proven) the Southern Hound was the ancestor of the smaller, lighter Talbot Hound. 

The Bloodhound specialized in following scents. These were 'tracker' and 'finder' dogs, which lead hunters to prey rather than taking part in the kill themselves. They were used to hunt down larger animals such as deer, wolves, or even people, and as such, size and endurance were more important than speed. 

As the centuries passed, the deer population dwindled and the need for a large-but-slow scenting dog decreased. Other smaller, faster dogs that could chase foxes became more popular and the numbers of Bloodhounds dwindled. 

The Bloodhound became the dog of poachers and bounty hunters, specializing in tracking down prison escapees or felons. In the modern day, this talent for tracking people makes them the natural choice as search and rescue dogs. 

The Science of a Bloodhound's Ability to Smell

Science of Can Bloodhound Dogs Smell Benzodiazepines?
Bloodhounds belong to a group of dogs that have developed their sense of smell at the expense of their other senses. This group is called "the scenthounds."

Scenthounds achieve their olfactory feats through a number of adaptations. For example, that large, damp nose helps trap odor particles and offer them up to the nasal chamber. All the while, those long ears flap around as the dog follows a scent, creating micro-air currents which waft smells towards the nose. 

The nasal chamber contains scrolls of fine bone that is lined with scent receptors. These are many times more numerous than in the human, meaning the dog is able to detect the faintest of smells. In addition, those scent receptors report to an olfactory center in the brain, which is several times the size of the equivalent in the human brain. Indeed, the scent center in a dog takes up about 2% of the brain, compared to just 0.03% in a human. This means a whole lot more processing power when following a faint odor. 

Training a Bloodhound to Smell Benzodiazepines

Training of Can Bloodhound Dogs Smell Benzodiazepines?
The idea behind sniffer dog training is to teach the dog to associate a certain smell with their favorite game or toy. Then, when the dog chooses the toy smelling of the drug, they are rewarded with a game or treat. 

To begin with, the handler uses a clean, scent-free towel, to engage the dog in an active game of tug. The dog is encouraged, praised, and rewarded for playing so that they look forward to these sessions. 

Then, the towel is infused with a faint odor of benzodiazepine and the dog plays with it. The next step is to offer the dog a choice of two towels, one of which is unscented and the other, smelling of benzodiazepine. If the dog chooses the unscented towel, they are ignored. If the dog chooses the scented towel, the handler praises them enthusiastically and plays tug. 

The dog is then given an even wider choice of potential tug toys, but is only rewarded for choosing the scented one. Once the dog is regularly picking out the correct towel, the handler partially hides it so that the dog has to use their sense of smell to find it. As the dog becomes more adept, the scented towel is hidden completely out of sight with the dog expected to sniff it out. 

How to React to a Bloodhound Sniffer Dog:

  • A sniffer dog has a job to do and should not be distracted. If you see a working Bloodhound, always speak to the handler before approaching the dog to check if it is OK to pet them.