[INTRO ♪]
When we need a little help sniffing something out,
we usually turn to our furry best friends.
And there's good reason for that: dogs are relatively easy to train,
and their sense of smell is as much as 100,000 times more acute than ours.
And they're cuter.
We have machines, sure, but electronic odor detectors
tend to struggle when the chemical of interest is in low concentrations
in a complex mixture of molecules, like, I don't know, the air.
So we've taught dogs how to sniff out
everything from sewage leaks to artwork-destroying insects.
But they're not the only critters whose sense of smell can be put to good use.
There are other champion sniffers that we could use
to detect everything from disaster survivors to gourmet fungi.
Here are six of the animal kingdom's most useful noses.
Truffles—the edible fungi that grow underground, and not the chocolates—
are a gourmet food that can fetch extremely high prices.
Since they're very hard to cultivate, they're usually gathered from the wild.
But finding fungi growing up to a meter underground is pretty challenging.
Luckily, pigs are here to help us sniff them out, and they have for centuries.
Pigs have over a thousand olfactory receptor genes in their genomes—
that's more than dogs, or us, so they're able to detect a wider variety of smells.
And their olfactory bulb—
the part of their brains that processes the information from smelling—
make up about 7% of their brain.
Your bulb is a mere 0.01% of your brain.
But the real reason we use them to hunt truffles
is that they seem to have a weird natural affinity for them.
In the 1980s, researchers discovered that truffles contain large amounts of
a musky steroid that boars secrete in their saliva to put their sows... in the mood.
So, many think that's what attracts the pigs.
But a study in 1990 suggested another compound—
dimethyl sulfide—was the odor instead.
And there hasn't been much follow up, so the jury is still out.
Either way, pigs' natural instinct to root around in the dirt
in search of food probably enhances their truffle-finding skills.
Though, apparently, the pigs are notorious for snacking on the goods they find,
and it's no picnic trying to wrestle a $1000 fungus from a 200-kilogram hog.
Which is probably why nowadays,
they're losing their truffle hunting jobs to trained dogs.
I guess natural talent just doesn't trump canine ease of use.
Detecting sick animals could help predict and track
outbreaks of diseases like bird flu that can jump from other species to our own.
But classic methods for detection, like blood tests,
require a lot of time and money for sample collection and analysis.
And why do that, when there's a living disease detector right under our noses?
Enter: Mice.
Like dogs and pigs, rodents have far more functioning genes
for odor reception than we do, so they're able to
distinguish between scents that we can't even smell.
And, relative to the size of their brains,
their olfactory bulb is 200 times bigger than ours,
and 5 times bigger than dogs'.
That, and their ease of breeding and care,
makes them ideal for use as biosensors: living chemical detectors.
In a 2013 study, researchers found that mice could sniff the difference
between the poop from healthy mallard ducks
and poop from ones infected with avian influenza.
The six trained mice managed to pick out the right poop about 80% of the time,
though that was under lab conditions—
it remains to be seen if they fare as well in the field.
But that hasn't stopped New York scientists from trying to take
the whole mouse biosensor idea to the next level using genetic engineering.
In 2016, they showed their "MouSensor" mice,
which are engineered with additional olfactory receptor genes,
can be up to one hundred times better than regular lab mice
at detecting particular smells—and those were just the pilot versions.
With results like that, it might not be long
before dogs start losing ground to super sniffing genetically modified mice.
Landmines left behind after conflicts kill thousands of people every year,
but finding and removing them is a dangerous and difficult task.
It's much safer for the humans involved if something smaller and lighter
can go through and flag where all the bombs are first.
People have used dogs for this, but they're expensive to train,
and hard to transport around the world.
So, a Belgian nonprofit enlists local noses instead—
those of Gambian pouched rats.
These so-called rats—which are actually members of
a different rodent family—are huge rodents native to central Africa.
They can be 75 centimeters from nose to tail and weigh over a kilogram.
Their vision is terrible, but they make up for it with an amazing sense of smell,
which they use to communicate with each other over long distances.
And that means their noses have no trouble detecting
small amounts of explosives like TNT, even if said explosives
are buried 20 centimeters below ground in a land mine.
They're also light enough to walk across minefields safely, and they're fast—
a single rat can check 200 square meters in 20 minutes,
which would take a person days to do.
The nonprofit calls their trained rodents "HeroRATS"—and it's easy to see why.
Gambian pouched rats helped clear over 13,000 mines in Tanzania,
Mozambique, Angola, and Cambodia between 1997 and 2015.
But the rats do require a rigorous training protocol
that takes the first nine months of their eight-year lives.
At least they look super cute in their special little harnesses!
After a disaster like an earthquake,
finding victims trapped in debris can be a slow, challenging process.
Search and rescue dogs and their powerful sniffers are a big help.
But often, a smaller, more agile critter would be even better.
Something like … a search and rescue cat!
Okay, cats aren't actually being trained to do this yet,
but experts argued in a 2017 paper that maybe they should be.
That's because, although we don't know as much about their sense of smell
as other animals, what we do know suggests they've got great noses.
For example, they have 30 variants of the V1R odor receptor gene—
dogs only have nine, and we only have two.
That suggests that they may be even better than dogs
at discriminating between some scents.
The scientists behind the 2017 review argue that this means they could
take over some of the scent-related jobs that dogs are trained to do now.
And since cats are better climbers and can squeeze into smaller spaces,
they might be better suited to searching for trapped people than man's best friends.
The problem is training them, but the researchers believe it's possible,
with proper socialization and the right rewards to motivate them.
I mean, if we can train pigs and mice and giant rats, how hard could cats be?
Though, that saying about herding cats does exist for a reason.
So whether cats will live up to their heroic potential remains to be seen.
When you're sick, you actually smell a little weird.
No offense.
The illness and your immunological reaction to it
alter the concentrations of some molecules in your bodily fluids.
I mean, you might not smell the difference, but bees can.
Though they don't have noses in the way we think of them,
honey bees do have an amazing sense of smell.
That's what allows them to sniff their way to food even if it's miles away.
And scents play incredibly important roles in bee social lives.
Which is why, in their genomes, they have 163 functional
odorant receptor genes—the smelling genes unique to insects.
Fruit flies, for comparison, which also have to sniff out their meals,
have less than half that number.
These diverse odor receptors allow bees to smell the difference
between subtly different varieties of the same plant.
And it only takes a single encounter with an odor associated with a reward,
like nectar, for a bee to be able to identify the smell again.
That makes it really easy to teach bees to detect a variety of chemicals,
including disease-specific odors on our breath.
A designer in the UK even invented a glass apparatus
that allows for diagnosis by bee.
The bees have to be trained on the smell of the disease in question,
but if a person with that condition breathes into the device,
the trained bees swarm towards their breath.
If they're not sick with the target illness, the bees don't react.
It's just a prototype, but it did work at least once,
identifying a confirmed case of diabetes.
And sure, dogs can perform a similar trick, but the bees are a lot easier to train.
It only takes about 10 minutes of training to get 98% accuracy from the bees,
whereas dogs take weeks and are only right about 71% of the time.
So making honey, pollinating plants, and now diagnosing diabetes—
is there anything bees can't do?
But bees aren't the only insects with smelling superpowers.
Wasps can get in on the act, too.
A tiny parasitic wasp called Microplitis croceipes
lays its eggs in the bodies of living caterpillars.
And it behaves differently when it smells its host as opposed to its food,
which means scientists can train a single wasp to identify two different smells!
On the downside, the wasps only live a few weeks,
and they only remember the scents they've been trained on for a couple days.
But on the upside, they're cheap to raise,
and are reportedly even easier to train than bees.
And according to researchers that have worked with them,
they can detect "almost anything"—they've trained wasps on explosives,
food toxins, and even the pheromones of bed bugs.
In trials, the wasps were at least ten times as sensitive
to the test chemicals as the best electronic sensors.
The researchers even invented a device
for harnessing the wasps' super sniffing ability.
They call it the "Wasp Hound", because it's kind of like having
a trained bloodhound… except it's a container of wasps,
that wiggle instead of howl.
The wasps are held in a cartridge, which is exposed to air samples.
Based on their movements, the researchers can tell
whether the chemical they've been trained on is present in the sample or not.
Sniffer wasps could be used for jobs considered
too dangerous for us or our loyal companions to perform.
But the startup hoping to market the wasps' mad sniffing skillz
hasn't been too successful, so it's unclear if wasps
will replace the hounds they're named after anytime soon.
But even if some of these examples are still conceptual,
it's pretty wild that all sorts of animals—
from those with backbones and four legs, to those with stingers and six legs—
have these amazingly useful olfactory abilities.
Whether it's ridding the world of dangerous explosives left over after wars,
or finding gourmet fungus growing underground,
these six animals follow their noses to do some incredible things.
If there's a scent we need to track down
that our human schnozzes can't detect,
there's probably a critter out there that can help us sniff it out.
Thanks for watching this episode of SciShow.
While our noses aren't quite as keen as the animals we just talked about,
they're not as bad at sniffing as you might think.
If you want to learn more about that,
you can check out our episode about human smelling abilities.
[OUTRO ♪]
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