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10 Animal Defense Mechanisms to Avoid Being Eaten

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Duration:09:18
Uploaded:2016-10-16
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MLA Full: "10 Animal Defense Mechanisms to Avoid Being Eaten." YouTube, uploaded by SciShow, 16 October 2016, www.youtube.com/watch?v=d6Q8F2dShFs.
MLA Inline: (SciShow, 2016)
APA Full: SciShow. (2016, October 16). 10 Animal Defense Mechanisms to Avoid Being Eaten [Video]. YouTube. https://youtube.com/watch?v=d6Q8F2dShFs
APA Inline: (SciShow, 2016)
Chicago Full: SciShow, "10 Animal Defense Mechanisms to Avoid Being Eaten.", October 16, 2016, YouTube, 09:18,
https://youtube.com/watch?v=d6Q8F2dShFs.
There are two major groups in the animal kingdom: predators, and prey. If you’re a wild animal, and fall under the prey group, you might spend your days actively trying to NOT become another animal's dinner. In the fashion of natural selection, some animals have come up with some pretty bizarre strategies to stay safe. Learn all about them with Michael Aranda in this new episode of SciShow!
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Sources:
Assassin bugs
http://www.smithsonianmag.com/science-nature/this-insect-uses-its-victims-carcasses-as-camouflage-83656246/?no-ist
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2007.00335.x/full
http://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(02)02519-3#back-BIB1

Moths
http://www.life.umd.edu/faculty/wilkinson/honr278c/PDF/Miller01.pdf
http://science.sciencemag.org/content/325/5938/325.abstract
http://jeb.biologists.org/content/215/24/4278.short
http://voices.nationalgeographic.com/2013/05/13/moths-superhearing-evolved-to-escape-bats/

California ground squirrels
http://www.pnas.org/content/104/36/14372.full
http://www.scientificamerican.com/article/squirrel-hot-tail-tell-snakes/

Bombardier beetle
https://www.youtube.com/watch?v=TgqF-ND2XcY
http://news.mit.edu/2015/how-bombardier-beetles-produce-defensive-spray-0430
http://science.sciencemag.org/content/348/6234/563

Black-capped chickadees
http://science.sciencemag.org/content/308/5730/1934
http://www.washington.edu/news/2005/06/23/chickadees-alarm-calls-carry-information-about-size-threat-of-predator/
http://www.raptorsoftherockies.org/html/chickadee%20overview.pdf
http://octavia.zoology.washington.edu/publications/BergstromAndLachmann01.pdf

Triggerfish
http://www.arkive.org/queen-triggerfish/balistes-vetula/
http://pubs.iclarm.net/libinfo/Pdf/Pub%20SR76%207.pdf
http://animals.nationalgeographic.com/animals/fish/triggerfish/

Boxer Crab
https://www.deeperblue.com/creature-feature-not-quite-muhammed-ali/
http://www.sciencedirect.com/science/article/pii/S0022098113002827

Hagfish
http://jeb.biologists.org/content/209/4/702.long
http://jeb.biologists.org/content/208/24/4613.long
https://books.google.co.uk/books?id=uBXTCQAAQBAJ&pg=PA259
http://voices.nationalgeographic.com/2014/04/22/hagfish-slime-animals-science-weird-fish/
http://www.nature.com/articles/srep00131
https://books.google.co.uk/books?id=FyehAR6hsUUC&pg=PA235

Thomson’s gazelles
https://www.jstor.org/stable/4600191?seq=1#page_scan_tab_contents
http://www.sciencedirect.com/science/article/pii/S0003347203003531

Ground beetle larvae
http://io9.gizmodo.com/5842323/this-beetle-larva-tricks-its-predator-into-becoming-prey
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0025161
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 Intro (0:00)


[SciShow intro plays]

Michael: Here’s a protip: If you’re an animal in the wild, try not becoming someone else’s dinner. You’ll survive longer and have a better chance of passing on your genes. You could blend in with the background, or disguise yourself as something unappetizing, like a pile of poop! Or you could do the opposite, and have garish colors to let predators know you’re toxic. There’s safety in numbers, so maybe some stranger will be eaten instead of you.

Or try waking up after your predators have gone to sleep. All kinds of antipredator adaptations have evolved across the animal kingdom, from physical features to behaviors. And some animals use pretty bizarre strategies to stay safe.

 1. Assassin bugs and their camo meat-shield (0:40)


Assassin bugs are named for their predatory skills, but they’re actually somewhere in the middle of the food chain. So there’s a species of assassin bug that avoids the wrath of its predators by wearing the corpses of its prey!

This bug is mostly an ant-killer, using sharp straw-like mouthparts to dissolve the tissue and suck out those nutritious juices. But instead of tossing the leftover exoskeletons, the assassin bug sticks them together with tiny threads and stacks them on its back.

Now, one of its predators is jumping spiders, which rely on their eyesight for hunting. And a 2007 study showed that jumping spiders are around 10 times less likely to attack corpse-laden assassin bugs than bare-backed ones. Researchers think the ant-corpse backpack changes the bug’s outline and movement – so predators that depend on vision just can’t tell that it’s food. Or if they did attack, they might just get a heaping mouthful of ant corpses as the assassin bug scurries away... which doesn’t sound all that delicious.

 2. Moths vs. bats: warning, jamming, and dropping out of the sky (1:28)


Instead of sight, bats hunt using sound, also known as echolocation. Basically, they call into the night at frequencies higher than we humans can hear. The audio signals that bounce back let the bat know what’s around: trees, buildings, or maybe a tasty moth.

Moths may seem like an easy meal, but that doesn’t mean they’re defenseless against their flying foes. Some, like the greater wax moth, have evolved the ability to detect high-pitched sounds, like bat echolocation clicks. If they sense a bat getting too close, they might fly in wild patterns, or even drop out of the sky to avoid being caught. Other moths take it farther and emit clicks of their own to freak the bats out, or tell them, “I’m not tasty, don’t eat me!”

Plus, a few species of tiger moth can even use their clicks to interfere with the bat’s echolocation, a process called jamming. Rather than detecting a clear “moth” audio pattern, the bat gets a garbled signal – and can lose track of the moth in its confusion.

 3. The California ground squirrel’s 'hot-tail’ (2:15)


California ground squirrel moms also have a few tricks up their tails to keep their young safe from hungry predators. First off, they’re tough and willing to fight – with sharp teeth and claws, and have even evolved resistance to rattlesnake venom. So lots of predators take heed of her warning signals. If it’s a mammal like a fox or badger, she’ll call loudly. Basically saying, “I’ve seen you. You better stay away.”

But predators like snakes probably don’t hear airborne sounds as clearly, or even at all, so shouting would be a waste of energy. Instead, she uses tail-flagging: waving her bushy tail to tell them to back off.

But that’s not all: some rattlesnakes have heat-sensing organs that detect infrared energy. If one of these rattlesnakes is prowling around, the California ground squirrels heat up their tails while tail-flagging – probably through increased blood flow. When the rattlesnakes get the message, their behavior changes dramatically, from predatory to defensive.

Researchers think this hot-tail action is a special adaptation, because the squirrels only use it with rattlesnakes – not gopher snakes, which can’t sense infrared. So evolution has given these mammals a bunch of strategies to help future generations survive.

 4. The boiling acid of bombardier beetles (3:12)


Bombardier beetles aren’t the most graceful things. They’re bulky, and even though they can fly, it takes a while to get airborne. But if one feels threatened, it can buy itself some time … with raw pain! Tilting its back end towards its aggressor, the beetle fires explosive pulses of boiling hot, toxic liquid. The beetle’s abdomen contains two separate chambers, storing hydroquinones and hydrogen peroxide respectively. These react violently into a hot, high-pressure spray of benzoquinones: chemical irritants that deter virtually all predators.

Researchers from MIT have been studying this superpower. They used synchrotron X-ray imaging to see inside the beetle as it detonates. The flexible membranes and valves they discovered were complex, but they were only a few evolutionary tweaks away from the beetle’s much-less-violent relatives.

Understanding how this insect creates and survives these intense chemical sprays could even help engineers develop beetle-inspired propulsion and blast-protection systems.

 5. Black-capped chickadee call signs (4:04) 


Next up are black-capped chickadees. They’re common North American birds, and tasty treats for many birds of prey, also known as raptors. But these little songbirds have surprisingly complex ways of communicating, with special calls that trigger fight or flight reactions.

If a chickadee spots a soaring raptor, ready to snatch a meal, it’ll use a soft, high-pitched “seet” call. This works like an urgent whisper: “get down now!” But a less immediate threat, like a perched raptor, is signalled by the famous “chick-a-dee” call, which can be a call-to-arms. The call rallies the whole flock, and even-- sometimes other species, to mob and pester the raptor.

With its cover blown, the predator’s best bet is to try elsewhere. Researchers think that chick-a-dee calls could encode some detail about the predator, as well. The more “dee” syllables, the bigger the threat level – and up to 23 “dees” have been recorded!

 6. Triggerfish lockdown with a fin (4:46)


The colorful, kind of goofy-looking triggerfish are found in warm ocean waters around the world, and play it safer than some of these other animals. They search the ocean floor for food, like molluscs and crustaceans.

But if threatened, they’ll head for the nearest cubbyhole to hide. See, triggerfish have two spiny dorsal fins that normally lie flat against their body. If they’re wedged in a crevice, they can lock these spines upright to stay in place. That way, it’s a lot harder for predators like tuna and dolphinfish to pull them out and swallow them.

The “trigger” is a shorter, wedge-shaped spine that controls the longer, main spine. Pressing the trigger down is the only thing that’ll flatten the dorsal fin, but predatory fish can’t really get to it, or even know that’s where the release-mechanism is.

A triggerfish does have muscular control over this trigger spine, though, and can flatten its fins again when it feels safe enough to leave its crevice.

 7. A crab with anemone boxing gloves (5:29)


Crabs use their claws for all kinds of things: grasping food, nipping an enemy, or even attracting a mate. But boxer crabs, also known as pom-pom crabs, use theirs for brandishing weapons... by dual-wielding stinging anemones, like tiny toxic boxing gloves! Boxer crabs and different anemone species have evolved symbiotic relationships.

The candy-striped crabs get protection from predators, usually small fish, who don’t want a face-full of stinging tentacles. In return, the sea anemones get a mobile bodyguard 24/7, and pick up leftover food scraps dropped by the crab. So it sounds like a pretty good deal, but this relationship might not be as mutually-beneficial as it seems.

A 2013 study found that boxer crabs only let their anemones feed for short amounts of times, stealing the rest of the food for themselves. This keeps the anemones way smaller than they would be if they just grew on the seafloor – almost like portable bonsai. So even though this relationship looks kind of cute, it’s actually more of a one-sided, parasitic deal.

 8. Slime and twist with the hagfish (6:19)


Hagfish, on the other hand, look about an unappealing as their name suggests. Their antipredator defense is pretty gross, too. If startled or grabbed by a predator like a shark, a hagfish will spew out a bunch of goopy slime from pores all over its body. The slime is made from mucins and other thread-like proteins that expand in water, creating a thick gel that gets everywhere!

Beyond just being gross, this mucus is potentially lethal. It’s not toxic, but it can clog the gills of attacking fish, probably by keeping water from flowing as easily. All of a sudden, the predator has to focus on not suffocating to death, rather than finishing its lunch. Plus, to make a speedy exit, hagfish can twist their flexible bodies into an “overhand knot” shape to wipe off the mucus layer and slip away.

Hagfish slime is an area of active research, as scientists try and figure out how the massively long protein fibers in the slime are stored and deployed. One lab is even talking about threading similar proteins into tough, stretchy clothing of the future!

 9. Pronking – Thomson’s gazelle (7:10)


Pronking, or stotting, may sound like some new internet fad, but it’s a move with a message that keeps some animals alive. In the African plains, herbivores like the Thomson’s gazelle tend to hang out in herds, keeping multiple eyes on the lookout for predators, like big cat species.

So, as a gazelle, you may have some safety in numbers, but you still want to make sure the predator isn’t going for you. Predators don’t want to waste precious energy on a failed hunt, so many of them choose their target carefully – maybe a weaker-looking gazelle.

So, some prey animals pronk! Basically, it’s a high leap in the air with an arched back, and all four legs straightened out. It might seem like a wasteful, energy-intensive activity, but some researchers think that’s the point. Pronking could show that a gazelle has strength to spare, and predators had better pick someone else for their dinner.

 10. Ground beetle larvae vs amphibians: become the predator! (7:52)


In many cases, the food chain is pretty well-defined: Like how lions eat zebra, how spiders eat flies, or how many amphibians eat ground beetle larvae. Well, most of the time. Once in a rare while, there’s an evolutionary role reversal.

Introducing the Epomis larva: when prey becomes predator! The lone larva acts all innocent and helpless, wriggling around to entice the would-be predators. For any other ground beetle larva, the high-speed lunge from a hungry frog would mean game-over. But Epomis larvae are ready and waiting: with a sudden head flick, the grub dodges the frog’s attack and strikes back. It latches on to the frog’s body with its tough jaws and starts to chow down, sucking out fluids and eventually eating away at the soft froggy flesh.

We’re not exactly sure how this switcheroo evolved, but when scientists conducted nearly 400 Epomis larva versus amphibian battles-to-the-death, the grub won every single time. So however these ground beetle larvae managed it, it’s working well for them now!


 Outro (8:43)



The animal kingdom can be pretty brutal, because everyone’s just trying to eat and stay alive. But evolution keeps things interesting, especially with all the creative adaptations in prey animals – from hiding, to making a scene, to really putting up a fight.

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