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Whether it’s for food, protection, or a little healthy grooming, a lot of animals of different species form some surprising mutualistic relationships in nature.

Hosted by: Hank Green

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[Scishow Intro].

Hank: In the wild, it’s easy to imagine that every species is out for itself. But animals of different species form all sorts of relationships in nature, and some of them are downright friendly.

That’s what you call mutualism: a relationship where both organisms benefit from the arrangement. Kind of like a “You scratch my back, I’ll scratch yours, because neither of us can scratch our own backs cuz our arms are wrong.” Such animal partnerships show just how interconnected the animal kingdom really is. So today, we’re gonna talk about 8 unexpected but very real animal duos, from hunting partners to grooming buddies, these animals make interspecies friendship look easy.

 Coyotes & Badgers (0:49)

Coyotes and badgers are both common predators in much of North America. But rather than fight for food, the two have been known to work together as hunting partners. You see, badgers generally hunt ground squirrels underground.

They put dead ends in their tunnels, then scare them into that trap and dig them out. Sounds terrible. They are not friends.

Not friends. Coyotes hunt these squirrels above ground by waiting until they venture far enough from their tunnels to pounce. And because their styles are so different, if these two predators team up, they can both benefit.

When squirrels detect a badger, they often run above the ground to escape, right to where coyotes are waiting. And when squirrels detect a coyote, they usually retreat to their tunnels, putting them right where the badger wants them. A 1992 study found that when working together, coyotes captured 34% more squirrels than working alone.

And while it’s harder to count the prey badgers catch when they’re in the dirt, badgers that work with coyotes spend more time underground. Biologists’ figure that’s because they’re hunting more or eating more, and either way, that’s a win for them. Both of these species are pretty smart and social and live fairly long lives, so it’s not too surprising that they’re able to form this kind of relationship.

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But scientists don’t see these pairings everywhere.

They seem to occur more often where there are more coyotes and badgers, which makes sense, because there are a ton of them around, they’re bound to run into each other. And that means there’s more opportunity for an accidental assist to lead to a lasting partnership.

They also seem to happen in areas where there’s a lot of dense, small bushes. These make it harder for both hunters to succeed solo, so the benefits of teaming up are all that more appealing.

 Gobies & Shrimp (2:26)

It’s not just predators that work together though, prey species can also team up for extra protection. One of the most well-studied mutualisms is one that occurs between snapping shrimps and gobies, a kind of small fish. Dozens of species of these animals pair up. The shrimp is really good at digging, so it digs and maintains a burrow for both of them.

The goby, meanwhile, has better long-distance eyesight, so it watches out for predators. And in many pairings, the two communicate through touch. The shrimp taps the goby with its antennae to let it know that it’s there, and the goby flicks its tail to tell the shrimp that trouble’s brewing.

Some species in this setup are obligate partners, meaning they literally don’t make it if they don’t have their brother from another mother, or like, I guess brylum from another phylum. Even when the partnership is optional, though, biologists have found that if you take away a shrimp’s fish buddy, it eats less, presumably because it’s more worried about being vulnerable while foraging. And in studies, gobies that don’t pair with shrimps tend to disappear.

Without their well-maintained panic room, they just get eaten. Of course, it’s not always a single shrimp-fish pair: both the shrimps and the gobies will live with their mates, too, bringing the twosome to a foursome, or even a fivesome, since the shrimps frequently form thruples instead of couples. This partnership makes a lot of sense from an evolutionary perspective.

Gobies are generally fond of hiding places, so it seems like they’d dart into a shrimp burrow on occasion. And the shrimps probably wouldn’t mind that, if having a goby roommate meant knowing when to duck underground.

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Then over time, selection favored individuals that formed partnerships, and the species began to influence each other’s evolution, or to co-evolve.

Some scientists think they’re seeing this happen in real time. They’ve found species of shrimps and gobies that are doing their individual jobs together, but without the specific communication system.

So basically, it’s the beginning of what is expected to be a beautiful friendship. Sometimes, though, a burrow isn’t cozy enough. Sometimes what you really need is a turtle butt.

 Crabs & Turtles (4:29)

Take it from oceanic crabs. They have been known to make a home on the butts of sea turtles, specifically, the little area between the tail and the upper shell. See, the crabs can’t swim very far, so they live on anything that floats. But they prefer places where they can hide, which makes turtle butts the obvious choice.

It’s a good home, too. The crabs on turtles tend to be big and healthy, suggesting they get plenty of food. They’re also more likely to be monogamous, since there’s room for two and only two.

And the females are more likely to be brooding eggs; a clear sign to biologists that turtle butt is awesome habitat. For awhile, it wasn’t clear what, if anything, the turtles got out of having these rear-end residents. Scientists used to think that the crabs ate the turtle’s poop, which would have made this a strictly one-sided relationship.

But studies of the crab’s stomach contents revealed that they actually feed on barnacles and other organisms that attach to turtles. Since these can damage the turtle’s shells and make it harder to swim, the crabs provide a valuable cleaning service. They’re like live-in maids.

On your butt.

 Mice & Beetles (5:35)

Some rove beetles live in the fur of small South American mammals, especially rodents. At first, scientists thought these beetles were parasites, though, that would have made them the world’s only blood-sucking beetles. But back in the 1980s, a pair of biologists questioned this idea. The mice didn’t seem to care that the beetles were there, which is weird, because these are not small beetles.

They’re about a centimeter long, on a roughly fifteen centimeter-long mouse.

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The beetles could even walk across their faces and the rodents didn’t do a thing about it.

But, when the scientists placed these beetles on another mouse species, things were totally different. The mice immediately scratched them off and killed them.

A closer look revealed that the beetles don’t feed on the mammals directly; they eat the fleas and ticks that do. So, they get a nice, cozy place to live and all the bugs they can eat. And it turns out the beetles only attach to the mammals’ fur at night when they’re active.

During the day, they just hang out in the nest. That is most likely how this mutualism started; the beetles stumbled upon the feast of parasites in the mammal’s nest and decided to stick around. At some point, they got so friendly with their furry roommates that they started hitching rides, that way, they wouldn’t miss a meal if the animal decided to spend the day somewhere else.

Some small mammals have several nests; others don’t have a formal nest, and just curl up wherever they see fit. So sticking with the source of their meal is kind of important. And intriguingly, this beetle-mammal pairing seems to happen on other continents, too.

There are a couple of species of rove beetles in Australia that sometimes hang out on rats and possums there. So far, we’ve mostly covered partnerships between species that wouldn’t otherwise bother each other.

 Frogs & Tarantulas (7:16)

But predators and their prey can team up, too. Look no further than frogs and tarantulas. Large spiders are opportunistic hunters that often eat frogs, but several species have learned to shack up with their potential food. These spiders let the frogs live in their burrows undisturbed, even though they still eat other frogs; they’re somehow able to tell frog species apart.

And scientists think this recognition is chemical. You see, when spiders grab a potential meal, first they ‘taste’ it with chemical sensors. And researchers have actually taken the skin from a spider’s partner frog species and glued it onto another frog that the spiders usually eat.

Lo and behold, when a spider grabs a frog wearing one of these skins, it lets it go, like,

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“You have no quarrel with me, little frog. You are wearing the skin of my friend.” The frogs clearly benefit from this partnership, because, like, they’re not eaten by the spider, and they get a safe place to hang out. In return, scientists think the frogs eat ants and other tiny insects that would otherwise attack the spiders’ eggs.

It’s not entirely clear how these particular frogs got so lucky, but the species involved may be generally toxic or otherwise unpalatable to the spiders. So it’s possible that spiders don’t really want to eat them in the first place, though how they learned to just let them chill in their burrow is still a mystery.

 Mites & Beetles (8:38)

Speaking of tiny bugs that like to eat eggs: mites are usually considered pests. But if you’re laying eggs in a popular egg-laying area, it’s good to have them on your side. Which is why some carrion beetles have struck a deal with them. As their name implies, carrion beetles eat dead things, and they lay their eggs in them, too.

Well, them and every other fly and beetle in the vicinity. So, to get a leg up on the competition, the carrion beetles let the mites ride around on them. The mites eat up all the other eggs and larvae they can find, leaving the beetles with the perfect nursery for their eggs.

In return, the mites get a free ride to food supplies they couldn’t otherwise reach. It’s so beneficial for the beetles and the mites alike that it has turned into a lifelong partnership. The mites reproduce in the same brood chamber as the beetles, so the mite babies can attach to the beetle babies from day one.

But it’s a delicate partnership. You see, if there are too many mites, they tend to start eating the beetles’ eggs, too, reducing the brood’s chance of survival. Too few mites or no mites at all doesn’t immediately harm the beetles, so you’d think that they’d err on the side of caution.

But without the mites, other critters, like, little worms called nematodes, reproduce unchecked, and the beetles end up carrying them along with them to each brood site. Those not-so-nice hitchhikers can harm the beetles’ young, either directly or by competing with them.

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So, without mites, every subsequent brood is a little less successful, fewer survive, and those that do are smaller.

So ultimately, it’s in both the mites’ and the beetles' best interest to team up.

 Sunfish & Seabirds (10:11)

Sunfish are the world’s heaviest bony fish, but they also have another claim to fame: they’ve been known to host more than 40 different parasite species. No one likes having parasites, but in the open ocean, there aren’t any, like, cleaner fish stations to stop at. So, these oceanic travelers head to the surface and follow flocks of seabirds instead. Birds have no problem lending a beak, since they get a snack in the process.

But it’s not exactly easy for them to spot a fish that’s underwater, even one as big as a sunfish. So the sunfish angle their huge bodies sideways at the surface and just sit there, patiently waiting for the birds to pluck off worms or other parasites clinging to their skin. People used to think that this cleaning behavior happened by accident.

Sunfish spend a lot of time in deep, cold water, so they thought this surface behavior was just them, like, basking in the sun to warm up. But scientists have found this idea questionable, since there’s no relationship between how long the fish spend in cold water and how long they spend basking. It makes a lot more sense if the basking is for parasite removal specifically.

These worms can cause serious damage, so it’s in the sunfish’s best interest to get them off.

 Mongoose & Warthogs (11:20)

Perhaps the cutest pairing in the animal kingdom is the one between common warthogs and banded mongooses. Not meerkat. Mongoose. It’s not quite Timon & Pumbaa.

We got real close, but it’s not. See, mongooses clean ticks and parasites off of the warthogs. If a group of warthogs runs into a band of mongooses, they signal their interest in spa services by lying down.

Then, the mongooses approach and give them a full body anti-parasite treatment. The warthogs get clean, the mongooses get a snack. And as the 2016 article in Suiform Soundings describing the behavior notes, it’s only one of a few known cases of a mammal cleaning another mammal species.

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And one other thing that stands out: it only seems to happen in areas with a good number of people, too, which might explain how the friendship formed.

You see, something similar happens with coatis, a small South American raccoon relative that looks surprisingly like a mongoose, and tapirs, an animal that is not all that different from a warthog. Both mongooses and coatis spend a lot of time around human settlements scrounging for food. And since garbage dumps are popular areas for wildlife, these animals end up spending a lot of time around other species.

Biologists think that they spent so much time eating next to other species, that eventually they got comfortable enough to start picking food right off of them.

 Outro (12:43)

As these 8 partnerships show, not every species is out only for themselves. Whether it’s for food, protection, or a little healthy grooming, a lot of animals have figured out that life can be a little bit easier when you have a little help.

After all, when you’re trying to survive in the wild, you need every friend you can get. Thanks for watching this episode of SciShow! If you think these animal friendships are pretty neat, you’ll probably love our episode on symbiotic bacteria.

And to stay up to date with all of our episodes, be sure click on that subscribe button! [Scishow Outro].