[♪ INTRO] We owe a lot to our senses. Whether it’s hearing, sight, smell, taste,
or touch — whatever combination we have allows us to experience the
world in pretty exquisite detail. But some animal senses are
so much more acute than ours that they’re basically superpowers. And we’re not just talking dog
whistles and eagle-eyed vision. From animals that can taste with their
whole bodies to those with incredible super-smell, the animal kingdom
gets a whole lot more extreme — and more fascinating. Like in these five examples. For context, biologically speaking, a sensory system is a group of specialized
cells tuned to a certain type of signal. When they get the signal,
they fire off a nerve impulse, and that causes some kind of response. For vision, those specialized
cells are called photoreceptors. Humans have four types of them, including
three that contribute to color vision, and each is tuned to a
different range of light waves. Our brains can decode the signals from these cells to discern millions of wavelengths,
which we then perceive as colors. But our eyes are far from the best.
Other animals can see more colors, in lower light, or with more detail. And when it comes to cool eye tricks, the
mantis shrimp leaves everyone in the dust. This aquatic creature has the
most complex eyes of any animal. Depending on the species, they can have between 16 and
21 types of photoreceptors! Most are tuned to narrow bands of wavelengths, from deep red to far ultraviolet—including
wavelengths that are invisible to us. But that doesn’t mean they can discern
more distinct colors than we can. Researchers hypothesize that they
can probably recognize far fewer — possibly just one color per type of photoreceptor. But they can also process
color information really fast. See, for us, color vision hinges on
decoding that happens in the brain, and this takes a little time. But in mantis shrimp, color
perception happens right in the eye. So, they can react to the situation more quickly. This speed is important for the mantis
shrimp’s dynamic, super-competitive lifestyle, which involves lots of flamboyant signaling,
fighting, and fast-action hunting. But speedy color vision isn’t their only
trick. They can also see polarized light. Polarized light happens when light
waves all vibrate in the same plane — like, when they’re all oriented up and down. This is in contrast to regular light, which is made of waves
vibrating in all orientations. To us, polarized light doesn’t really
look any different from regular light. But some animals, like mantis shrimp, can see it, and they use it to glean important information. Not only that, but mantis
shrimp are the only animal known to be able to perceive circular polarized light. That’s polarized light that also spirals in
a clockwise or counterclockwise direction. They even have areas on parts of their bodies
that reflect this strange light pattern! That may help them communicate
with each other or identify mates. And newer evidence suggests
that their complex visual system may also help them learn and remember
information about their surroundings. Next, in stark contrast to mantis shrimp,
the star-nosed mole is practically blind. But vision isn’t very important for it anyhow, since it spends most of its time
in dark underground tunnels. Plus, it has a super-sense that more
than makes up for its poor eyesight. Maybe unsurprisingly, it has to do with its nose. Which is so distinct, it gives
the star-nosed mole its name. But their star-shaped snout
isn’t so much for smelling. In fact, its pink, fleshy appendages
don’t have smell receptors at all. Instead, they’re covered in mechanoreceptors. Mechanoreceptors respond to physical changes. So, when something stretches or pushes
on them, they fire off a nerve signal. When there’s a bunch of them spread
across an area, like your fingertips, they can gather information about
features like shape, texture, and size. And overall, something like your
fingertip is pretty sensitive. But this mole’s centimeter-wide star
packs about five times more sensing power than you have in your entire hand. In fact, it may be the most
sensitive touch organ in any mammal. And it gives the star-nosed mole unmatched
precision and speed. Like, officially. The Guinness Book of World Records has
named it the world’s fastest eater, in the mammal category. These little animals are voracious predators, and they use their star to forage for
invertebrates on their damp tunnel walls. Their nose’s super sensitivity
lets it find the tiniest prey— ones that are too small for
other predators to bother with. But on the flip side, because
their food is so small, they have to find a lot of it.
And here, too, the star delivers. As a mole forages, it touches its
star to up to 13 places per second. And it’s so good at collecting information
about things like size and texture, that it can decide within about 25 thousandths of
a second whether something is edible.
It’s also helpful that the
mole’s food-finding apparatus is optimally located right by its mouth,
and this likely adds to the speed. In a simulated tunnel experiment, one mole found and consumed 8
pieces of food in just 1.8 seconds! Another animal that uses super-sensitive
touch to hunt is the harbor seal— but in a very different way. Seals are pinnipeds—a group that also includes walruses and eared seals, like sea lions. And these animals are known for having
extraordinarily sensitive whiskers. The base of each whisker is
packed with mechanoreceptors. And compared to other mammals like your cat, pinnipeds have about ten times
more nerve endings per whisker. That makes them sensitive
to the tiniest movements. And sort of how like people use their
fingertips, pinnipeds can pass their whiskers over an object to quickly and accurately
sense its size, shape, and texture. Walruses, for example, use their whisker
touch to find edible items on the seafloor. But most true seals, like harbor
seals, take it up a notch. They can use their whiskers to sense
and follow trails of water disturbances that other animals or objects leave behind. Scientists think this helps them
hunt for their main food source: fish that swim in the water column. And their unusual whisker shape makes
them uniquely well-suited to this task. Other animals, even other pinnipeds,
have smooth, cylindrical whiskers. But true seals have flattened,
wavy-looking or wiggly-looking whiskers. A 2020 study showed that this
shape reduces drag in the water and reduces whisker vibrations as the seal swims. Since there’s little interference
from the seal’s own movements, it’s more sensitive to the
trails of other objects. And seals can extract impressive
details from these fleeting trails, including the size and shape of the object
that left it and the direction it was moving. Even after the thing that made
it has moved tens of meters away. In other words, never play
Marco Polo with a harbor seal. Next up are catfish. Catfish are bottom-dwellers that typically
live in dark, murky places. And although their eyesight is decent, their super-tasting
ability is what helps them find food. Compared to what we can do,
it’s also a little disturbing. So, taste relies on chemoreceptors— sensors that are activated when they
bind to certain molecules, or chemicals. And while our taste receptors
live mostly in our mouths, some animals have them in weird places. Like, flies and butterflies
can taste with their feet, and octopuses taste with their tentacles. But catfish can taste with their entire bodies. Basically, they can taste
anything that touches their skin, including water that’s recently passed
over something that they might want to eat. But instead of responding to
sweet, sour, or salty tastes, they’re highly sensitive to certain amino acids. Amino acids are the building blocks of
proteins, so they’re found in all living things. But the key here is that these molecules
are released in high concentrations by catfish’s favorite food: aquatic invertebrates. Now, we can taste amino acids
too, but catfish can sense them at concentrations 100,000
to one million times lower. And because their sense of taste is spread around, they can even tell what direction a
taste is coming from and hone in on it. The taste receptors are more concentrated
in certain places, though— like the fronts of their fins, which helps the catfish
pick up on taste trails as they swim. And they’re especially dense on the fleshy, whisker-like things around
their mouths, called barbels. So, as catfish forage for
food, they brush their barbels along muddy stream beds—or, for
marine species, the ocean floor. And when the signal is strong
enough, the taste of amino acids can make them start snapping their
jaws at the surrounding water. But that’s not the only unusual sensing
ability that sets catfish apart. In a 2014 study, researchers
found that at least one species can sense tiny decreases in water pH, or acidity. It’s not yet clear if this is
a function of their taste buds, but it fires up the same nerves. Either way, pH-sensing appears to
help them find tasty, little worms— since when the worms exhale carbon dioxide, it combines with the water
nearby to make carbonic acid. Our final animal is bears,
known for their super-smell. Smell uses chemoreceptors, kind of like taste. But these receptors bond to molecules
that move through the air, specifically. Now, considering that dogs can sniff out
things like drugs, money, and even cancer, it’s not surprising that
humans aren’t going to win any awards in the smell department. But bears are especially impressive. Like other animals with keen noses, they just have more real estate
dedicated to sensing smell. In fact, compared to us, some bear
species have five times more brain space dedicated to smell, and about 100
times more area inside their noses. Their sense of smell is not only keen
but also remarkable for its range— a distance that’s measured in kilometers. In fact, the range is so great
that it’s really hard to measure exactly how far it extends. Long-distance smell is useful because
most bear species roam over large areas, and it keeps them up-to-date
about what’s going on around them. Like, it can help them track their kids,
sense potential mates, and sniff out food. And lots of bear species seem to have this gift— as a fair number of backpackers will tell you. Like, in Yosemite National Park, black
bears can sniff out food hidden in a car— even crumbs and food residues. And
then rip the car apart to get it. And polar bears? They can
pick up scents on the wind and track them to seal breathing
holes up to three kilometers away. Bears’ keen noses may also help
them communicate with each other through scents left behind in their footprints. Like, male brown bears have a certain way
of grinding their feet into the soil when they really want to leave their scent behind
and let females know they’re available. And pandas can smell 120-day-old
scents left behind by other bears. Which is just, well, humbling. So, we humans like to think we’re the best because of our big brains and
ingenuity—and those are pretty great! But it’s also worth sitting back
and just admiring how other animals get to experience the world, too. Because there’s a lot to smell, taste,
hear, and see out there, and sometimes, the only way we can learn about it is by
watching the rest of the animal kingdom. This episode of SciShow goes
out to our patrons on Patreon! You might not have a star-shaped
snout or be able to taste things with your entire bodies, but we
still think you’re pretty incredible. Thanks for supporting free
science education on the internet— we couldn’t do this without you. If you’re not a patron, thank you for
supporting us by watching the show! If you want to learn more about our Patreon, you can also go to Patreon.com/SciShow. [♪ OUTRO]
