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To humans, drool can seem pretty disgusting, but other animals use saliva in surprising ways. Here are some of the weirdest ways other animals use their spit to survive!

Hosted by: Stefan Chin

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{ ♪INTRO }.

Whether it’s a drool stain somebody left on your pillow, or a slobbery hello from your dog, saliva can seem pretty disgusting. But there’s more to it than what--sometimes literally -- meets the eye.

Although saliva isn’t exactly the most glamorous fluid, it moistens our food, helps us swallow, breaks down starches, and protects us from disease. And that’s just the tip of the iceberg. Other animals use saliva for even cooler, more unexpected tasks like to attract mates, or maybe even decide their future careers.

Here are three of the weirdest ways other animals use their spit to survive. Up first, red kangaroos. These animals are the world’s largest marsupials, hanging out in harsh, arid regions of Australia.

If you couldn’t tell by their amazing boxing physique, they’re incredibly athletic and can reach speeds over 55 kilometers per hour. As large, active animals in a hot and dry environment, they also have several adaptations for keeping cool as the temperatures rise. While bounding across the grasslands, kangaroos definitely break a sweat, and much like dogs, they also pant under hot conditions.

But on top of these common strategies for regulating temperature, kangaroos also soak themselves in their own saliva to cool down. Seems a little gross, but it’s totally effective. See, kangaroos have a complex network of blood vessels just under surface of the skin on their forelegs.

When they’re feeling the heat, blood flow increases to this area, and by licking and soaking their skin with saliva, kangaroos can promote greater heat loss. This is thanks to saliva’s heat capacity, or its capability to absorb heat. Saliva is mostly made of water, which has a high heat capacity.

That means that it takes more heat to increase its temperature compared to other substances. So as the water in the saliva warms up and evaporates from a kangaroo’s arms, it absorbs some of the heat from this vessel-loaded area and cools down their body. Although this adaptation is shared with other species of kangaroos, it’s especially obvious in red kangaroos.

So look out for their spit-soaked arms the next time you’re in Australia. Now, you might not think that producing a lot of saliva would be helpful when it comes to impressing a mate in fact, you’d probably assume the opposite. But for some species of insects, their spit can play a key role in finding love.

Like with scorpionflies! These flies get their name from the scorpion-like “tail” on their abdomen, which is actually just their terrifying-looking male genitalia. But that’s not the weirdest part of their mating habits.

Like many other animals, some of the male flies will provide their potential mates with a nuptial gift to woo them. Sometimes this comes in the form of captured prey, like a smaller dead fly, but the most valued gift of all which often comes from healthy males is a spitball! Males offer up a mass of saliva, and these apparently-tasty secretions result in higher reproductive success compared to males who don’t go the spit-route.

And the bigger the mass of spit, the better! That’s because the female actually consumes the ball during mating, so when there’s a bigger gift, she takes longer to eat, and mating lasts longer, which means the male has more time to transfer his sperm and spread his genes. And you thought flies weren’t romantic.

And finally, ants might not use spit to cool down or woo females, but the way they do use it might be even weirder:. For them, swapping saliva might actually help determine their future careers. As gross as it might sound, mouth-to-mouth communication is really common in ants.

It’s called trophallaxis and is often a way to share food between members of a colony. But it may also influence what an ant larva grows up to be. An ant colony is made of various castes, which play differing roles within the group.

And while a lot of factors contribute to what an ant ultimately becomes including genetics, nutrition, and their environment compounds passed through trophallaxis might also play a surprisingly large part. In one study published in eLIFE in 2016, scientists analyzed the saliva being exchanged with larvae of Florida carpenter ants. They discovered that the fluid carried proteins, small RNA molecules, and something called juvenile hormone, which is known to impact larval growth, as well as physical and behavioral development.

Getting this hormone likely influences what ants grow up to become and their roles in the colony. Because of how these chemicals change their bodies and behavior, they may become small worker ants, larger soldiers, or even future queens. It’s actually similar to a behavior among honeybees, where worker bees feed so-called "royal jelly" to larvae destined to become new queens.

And you thought the kangaroos were strange. So, you might have thought of saliva as something pretty straightforward, fighting off bacteria in your mouth and helping you swallow those large spoonfuls of sticky peanut butter. But for some animals, it’s a lot more useful.

That being said… I am very glad my career wasn’t decided through trophallaxis. I’ll take resume workshops any day. Thanks for watching this episode of SciShow, especially to our patrons on Patreon!

We really appreciate your support, and this show wouldn’t be the same without you. If you want to help us keep making videos like this one, go to patreon.com/scishow. { ♪OUTRO }.