The Most Extraordinary Defense Mechanisms in the Animal Kingdom: A Visual Guide

Every animal alive today is the descendant of something that did not get eaten. That is the whole story of this guide. Four billion years of predators pushing, and four billion years of prey pushing back, and what you get at the end is a beetle with a combustion chamber in its abdomen and a snail that dresses in iron.

We have been collecting these since the site began, one glass frog and firehawk at a time. Here they are together, sorted not by animal but by strategy, because the strategies are the interesting part.

Poison is one answer to the same question. So is lying. So is giving up a piece of yourself and walking away. Some of the animals below are famous. A few have been photographed only a handful of times. All of them are real, and every number here comes from a published study, because the truth in this subject is stranger than anything we could improve on.

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• 01 · Chemical Warfare
• 02 · The Art of the Lie
• 03 · Parts for Sale
• 04 · The Last Resort
• 05 · Bone and Iron
• 06 · Jamming the Signal

01 · Chemical Warfare

The oldest trick in the book is to be unpleasant to eat. Some animals borrow their poison from their food. Some brew it. One of them cooks it, in real time, inside its own body.

1. The bombardier beetle runs a chemistry lab at boiling point

Inside the abdomen of a bombardier beetle are two reservoirs, one holding hydroquinones and the other hydrogen peroxide. On their own they are harmless. When something grabs the beetle, a valve opens and the mix drops into a thick-walled reaction chamber lined with enzymes, and the reaction that follows is violent enough to bring the liquid to roughly 100°C and flash part of it into steam. The pressure blows it out of the beetle’s rear, aimed, with a pop you can hear.

The famous detail is that it is not one squirt. High-speed film by Thomas Eisner’s lab in 1990 showed the spray arriving as a train of pulses, around 500 per second, and later X-ray imaging at MIT found the pulsing is passive: each tiny explosion slams the inlet valve shut, the pressure drops, the valve reopens and the next charge drops in. The beetle is not firing a machine gun. It is running a pulse jet, and it has enough fuel for about twenty rounds.

2. The Texas horned lizard shoots blood from its eyes

When a coyote or fox gets too close, the Texas horned lizard tightens muscles around the veins leaving its head. Pressure builds in sinuses beside the eyes until the thin vessels in the eyelid rupture, and a fine stream of blood shoots out, up to about five feet, sometimes more than once. The blood carries a chemical, probably picked up from the harvester ants the lizard eats, that canids find revolting. They gape, shake their heads and walk away.

What we love is how specific it is. Field researchers found the lizards fire readily at dogs, foxes and coyotes but almost never at hawks or snakes, which do not seem to mind the taste. The lizard knows its audience. It also pays for the show, losing a meaningful fraction of its blood in a single episode, which is why it tries everything else first: freezing, running, puffing up, presenting its horns. The blood is the last word.

3. The hagfish chokes sharks with a bucket of slime

A hagfish has no jaws, no proper eyes and no spine, and it has been around for 300 million years, so it is doing something right. Along its flanks are rows of slime glands packed with two kinds of cells. One holds mucus. The other holds a single protein thread, wound up like a skein of yarn, up to 22 centimeters long. Bite a hagfish and the glands nearest the bite fire into your mouth, seawater rushes in, the mucus swells and the threads unspool and tangle into a fibrous net that expands about ten thousand times in under half a second.

Baited cameras off New Zealand caught it working on sharks, conger eels and wreckfish. In fourteen attacks, every predator gagged, convulsed its gills and backed off, and every hagfish swam away unhurt. The slime gets stiffer under suction, which is exactly what a fish uses to feed, but flows easily under shear, which is what the hagfish uses to escape its own trap: it ties itself in a knot and slides the knot down its body like squeezing a tube.

4. The hooded pitohui is a bird you cannot touch

In 1989 an ornithologist named Jack Dumbacher scratched his hand on a pitohui in Papua New Guinea, licked the cut, and felt his mouth go numb and burn. The bird’s skin and feathers turned out to carry batrachotoxin, the same molecule that makes poison dart frogs deadly, and it was the first documented poisonous bird. Local hunters had known for generations. The name pitohui is roughly Papuan for rubbish bird, meaning do not bother cooking it.

The pitohui does not make the toxin. It appears to collect it from small Choresine beetles found in its stomach, and birds in beetle-poor forests carry almost none. The dose is far below the frog’s, enough to deter a snake or a hawk and to keep parasites off the feathers, not enough to kill you. Two more toxic New Guinea birds were confirmed in 2023, so the list is still growing.

5. The golden poison frog is two inches of pure deterrent

Phyllobates terribilis lives in one corner of Colombia’s Pacific rainforest and is about the size of a bottle cap. Its skin holds around a milligram of batrachotoxin, which jams open the sodium channels that nerves and heart muscle depend on. The usual line is that one frog carries enough to kill ten people, which is an extrapolation from mouse studies and has never been tested, for obvious reasons. The Emberá people simply rub a dart along the frog’s back, and the dart stays lethal for a year or two.

Like the pitohui, the frog is a collector, not a chemist. Wild frogs get their poison from the beetles and mites they eat, and frogs raised in captivity on crickets are harmless. The frog’s own sodium channels carry a mutation that keeps the toxin from affecting it, and the color is the point: that yellow is a warning label, printed in the one language every predator in the forest can read.

6. The slow loris is the only venomous primate

It looks like a stuffed toy, which is part of the problem. When threatened, a slow loris raises both arms above its head. This is not surrender. On the inside of each upper arm is a gland that secretes an oily fluid, and the loris licks it, mixing it with saliva to activate it, then delivers it through grooved lower teeth in a bite that causes slow-healing, necrotic wounds. One human death from anaphylactic shock is on record.

The surprise came in 2020, when an eight-year study of wild Javan slow lorises found that the venom’s main use is not against predators at all. It is for each other. Over half the males and a third of the females carried scars from venomous bites in territorial fights. Mothers also lick their infants with it before leaving them alone in the trees, which makes it the only case we know of a parent poison-proofing a child.

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02 · The Art of the Lie

Not every defense is a weapon. Some of the most effective are performances, and the best performers in the animal world would not be out of place on a stage.

7. The mimic octopus changes costume depending on who is watching

Discovered off Sulawesi in 1998, the mimic octopus lives on bare sand with nowhere to hide, so it hides in plain sight as something else. It flattens its body and ripples across the bottom like a toxic flatfish. It splays its banded arms like a lionfish. It sinks six arms into the sand and waves the other two in opposite directions, striped, like a banded sea snake. What makes it different from every other mimic in nature is that it chooses. When damselfish harassed one, it switched to the sea snake, which eats damselfish.

You will read that it impersonates fifteen species. The peer-reviewed count is three. The rest are diver stories, and we suspect some of them are true, but three is already the most any animal has been shown to do on purpose.

8. The hognose snake dies dramatically, then checks if you are still watching

The eastern hognose starts with a bluff: it flattens its neck into a cobra hood, hisses, and strikes with its mouth closed. If that fails it commits to a different genre entirely. It flips onto its back, writhes, lets its tongue loll out of a gaping mouth, releases musk and feces, sometimes bleeds a little from the mouth, and goes limp. Turn it right side up and it will roll over again, because a proper corpse is on its back.

Then it watches you. A classic 1988 study found the snakes revived sooner when the human observer looked away, which means the performance is being monitored from inside. One individual held the pose for 45 minutes. We should add that the hognose is mildly venomous, with rear fangs tuned to deflate puffed-up toads, and is entirely harmless to people. The whole thing is theater.

9. The killdeer fakes a broken wing and leads you away from the nest

The killdeer is a plover that nests on open gravel with no cover at all, and it has no way to fight anything. So when a fox approaches, the parent runs off calling, drops, drags one wing, fans its rusty tail and staggers along the ground as the most tempting easy meal a predator has ever seen. It always staggers away from the nest. When the fox has followed far enough, the wing is miraculously healed and the bird is gone.

The act is tuned to the threat. A cow, which would not eat the eggs but might step on them, gets a different show: wings up, charging straight at it, which occasionally gets the bird trampled. Males take more risks than females and display closer to predators, and the whole routine peaks during incubation, when the eggs are worth the most.

10. A caterpillar in Peru turns into a snake on demand

Hemeroplanes triptolemus is a plain brown hawkmoth. Its caterpillar is something else. Disturbed on a leaf, it drops and hangs by its back legs, pulls air in through its breathing holes and inflates its front segments into a triangular head with two big glossy eyespots and scale patterns on the underside. Then it twists to face you and lunges, a mock strike from an animal with no teeth and no venom, and the birds fall for it, because a bird that pauses to check whether a snake is real is a bird that gets eaten by the real ones.

The strangest part is that the caterpillar does all this upside down, hanging by its rear. The disguise only exists for the few weeks it spends as a larva. The adult moth gives up impersonation and simply looks like bark.

11. Zebra stripes are not for lions. They are for flies

For a century the argument was that stripes confuse lions. A 2019 experiment on a farm in Somerset settled it another way. Researchers filmed horse flies around zebras, horses, and horses wearing striped coats. Flies circled and approached zebras just as often as horses, but they failed to land. They came in fast, did not slow down, and bumped off or veered away, as though the stripes broke the last moment of their approach. Flies that did land on a zebra stayed about a second before being swished off, against ten seconds on a horse.

Horse flies carry diseases that kill, so this is a defense in every sense. It is just aimed at a predator small enough to overlook. The pattern that made the zebra an icon turns out to be an insect repellent you can see from a mile away.

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03 · Parts for Sale

If you can grow it back, you can give it away. A surprising number of animals treat pieces of their own body as the price of admission to tomorrow.

12. Lizards leave their tails behind, still moving

Tail loss looks like an injury. It is a mechanism. A lizard’s tail vertebrae have preformed fracture planes, and the muscle, skin, fat and blood vessels are all segmented to match. When a predator grabs on, the lizard itself does the breaking: muscles contract, the tissues unstick along the plane, sphincters clamp the artery, and the tail comes away almost bloodless. Then it thrashes. Shed leopard gecko tails flip and jump for a minute or two and keep swinging for up to half an hour, holding the predator’s attention while the owner leaves.

The tail that grows back is a cartilage tube rather than bone, a slightly different color, with no fracture planes of its own. So a lizard gets one drop per section, and the second break has to happen higher up than the first.

13. The fish-scale gecko sheds its skin in a predator’s mouth

Geckolepis megalepis, described from a limestone massif in northern Madagascar in 2017, has the largest scales of any gecko relative to its size, and they are barely attached. Beneath them the skin sits loosely on the body along a preformed splitting zone. Bite one and the predator gets a mouthful of scales and skin while a small, pink, naked gecko sprints away. The tearing is controlled from inside, with blood vessels clamping down and cells contracting, and the whole coat regrows in a few weeks without a scar.

It is so eager to shed that the scientists who named it had trouble getting a specimen with enough scales left to describe, and ended up identifying it from micro-CT scans of the skeleton instead.

14. The sea cucumber fires sticky threads out of its rear, then grows more

Several sea cucumbers keep a bundle of blind-ended tubules at the base of their breathing organs, and when a crab starts nosing around, the cucumber points its rear at it, takes in water, contracts hard enough to tear its own body wall and shoots out a handful of them. On contact with seawater the tubules stretch to many times their length and turn instantly, ferociously sticky. Crabs and sea stars were immobilized in nearly every trial researchers ran, and predators that had touched the threads avoided the cucumber for days.

It only fires ten to thirty at a time, from a stock of many more, and each one regrows in about five weeks. The researchers who worked it out called it an almost inexhaustible defense at limited cost, which is the kind of sentence that makes us want to be a sea cucumber. Other species skip the threads and simply eject their entire digestive system, then regrow it.

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04 · The Last Resort

Sometimes the defense is the whole animal. These are the ones that spend their own lives, or their children’s, to protect everyone else.

15. Exploding ants take the intruder with them

In the canopy of Borneo lives Colobopsis explodens, a small reddish ant whose minor workers carry poison glands running the full length of their bodies. When a rival ant, usually a weaver ant, refuses to back off, the worker grabs it, presses its abdomen against it and squeezes until its own body wall tears at the seams, spraying both of them with a sticky, toxic, bright yellow goo. The worker dies. The intruder is glued in place, poisoned, or sent running. The researchers who described it in 2018 noted that the goo smells faintly of curry.

It is not reflexive. The ant warns first, raising its rump, and only ruptures if the threat keeps coming. The big-headed major workers never explode. Their job is to plug the nest entrance with their faces.

16. Old termites wear explosive backpacks

A termite in French Guiana, Neocapritermes taracua, may have the most elegant chemistry on this list. Its workers carry two pouches of blue crystals on their backs, made of a copper enzyme. In their salivary glands, separately, they store harmless hydroquinones. Neither is dangerous alone. When the worker is attacked it ruptures, the two mix, and the enzyme instantly converts the hydroquinones into a toxic, sticky benzoquinone droplet that kills or maims whatever is biting it.

The pouches grow as the termite ages. Young workers with sharp mandibles are useful foragers and carry almost nothing; old workers whose jaws have worn down carry the largest bombs. The colony has arranged things so that the least useful members become the most dangerous. A 2024 study finally solved the enzyme’s structure and found a rare chemical bond that keeps it stable as a solid crystal on a living back, waiting.

17. Japanese honeybees cook hornets alive

A single giant hornet scout can wipe out a hive of European honeybees, which have no answer to it. Japanese honeybees have one. When the scout enters, several hundred workers pile onto it in a tight ball and vibrate their flight muscles until the interior reaches about 46°C. The hornet dies in under ten minutes. The bees, whose lethal limit is a few degrees higher, survive. It is one of the only known cases of an animal using heat as a weapon.

The subtle part came later. Hornets can actually tolerate 47°C for ten minutes in normal air. What kills them is that the bees’ breathing pushes carbon dioxide inside the ball to over three percent, which lowers the hornet’s heat tolerance below the bees’. It is a slow, cooperative, precisely calibrated execution, and the bees that take part age faster and die sooner for having done it. We have written before about their Himalayan cousins, who ripple in shimmering waves to scare hornets off before it comes to this.

18. The fulmar chick spits oil that grounds eagles

Fulmars nest on sea cliffs and leave their chicks alone on the ledge for hours. The chick is fat, flightless and looks helpless. It is not. Fulmars digest fish into a concentrated stomach oil, roughly as energy dense as diesel, and a chick that is approached will spit it in an aimed jet a meter or more, several times in a row. On a mammal it just smells appalling for years. On a bird it is catastrophic: the oil mats the feathers, ruins their waterproofing and insulation, and a gull or skua or raptor that takes a full hit can end up waterlogged, grounded and dead of exposure.

In a 1974 study, five of six oiled birds died. Hatchlings can spit through the crack in the egg before they have even finished hatching. The name comes from Old Norse for foul gull, which is fair.

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05 · Bone and Iron

Then there are the animals that simply cannot be eaten, or at least cannot be eaten conveniently. Armor in nature runs from fingernail to iron ore, and two of the animals here build their weapons out of their own skeletons.

19. The pangolin makes lions give up

A pangolin is covered in overlapping plates of keratin, the stuff of fingernails, arranged so that every scale is overlapped by three above it. Scales and skin together are about a quarter of the animal’s weight. Threatened, it rolls into a ball, tucks its face under its tail, and can flex so that the sharp scale edges slice a probing mouth. Lions try. There is footage from the Masai Mara of a lion rolling one around like a football before giving up, and a night at Londolozi where a whole pride worked on a balled pangolin from sunset into darkness and left in the morning without a single loose scale.

The tragedy is that a defense built on holding still is perfect against a lion and useless against a person, who simply picks the ball up. The armor that beats the apex predator is why the pangolin is the most trafficked mammal on earth.

20. The diabolical ironclad beetle survives being run over

Phloeodes diabolicus is a drab, flightless beetle from the oak woodlands of California, and it can be run over by a car and walk away. In 2020 a team at UC Irvine and Purdue put it in a press and found it withstood about 150 newtons before anything gave, roughly 39,000 times its body weight. Other beetles failed at less than half that. The secret is that its wing cases, useless for flight, have fused along the back into a seam shaped like interlocking jigsaw pieces. Under load the joint does not snap. Its layers peel apart gradually, spreading the strain through the body instead of concentrating it.

Entomologists have known about this for a long time in a different way: the beetle bends steel pins, so museum specimens have to be drilled. The 2020 paper was published in Nature and has since been borrowed by engineers designing aircraft joints.

21. The scaly-foot snail builds its shell from iron

Around hydrothermal vents in the Indian Ocean, nearly three kilometers down, lives the only animal known to build iron sulfide into its skeleton. The scaly-foot snail’s shell has three layers, an outer skin of iron minerals, a thick springy organic middle and a hard inner shell, and together they crack in a way that blunts and deflects a crab’s claw rather than giving in to it. Its foot is armored in hundreds of overlapping iron-coated plates. Its heart is enormous, about four percent of its body, to pump blood past the bacteria in its throat that feed it, because as an adult it does not eat at all.

At one vent field the same species grows white instead of black, because the water there does not carry enough iron to build with. In 2019 it became the first animal listed as endangered because of deep-sea mining.

22. The pufferfish is a balloon that is also poison

A pufferfish has no ribs and no pelvic bones, a stomach that stretches like a balloon and skin whose collagen is folded into pleats. Threatened, it pumps water in until it is three or four times its normal size, a stiff sphere too big and too awkward for most mouths. If that fails, it is one of the most poisonous vertebrates alive. Tetrodotoxin, concentrated in the liver, ovaries and skin, is more than a thousand times more potent than cyanide, has no antidote, and leaves its victim conscious while paralyzed.

The fish does not make the toxin. Bacteria in its food chain do, and puffers raised on clean diets are harmless, which is why some Japanese farms sell toxin-free fugu. Even so, around fifty people a year in Japan are poisoned, almost all of them by preparing it at home.

23. The hairy frog breaks its own bones to make claws

The Cameroonian hairy frog gets its name from the fringe of skin filaments breeding males grow along their flanks, which are for breathing underwater while guarding eggs and have nothing to do with defense. The defense is in the feet. Each hind toe holds a sharp bone claw tethered to a small bony nodule. When the frog is grabbed, a muscle pulls the claw so hard that it snaps free of the nodule and punches out through the skin of the toe pad, giving the frog a set of bare bone spikes. There is no keratin sheath. These are broken bones, deployed.

How they go back in has never been observed. The leading guess is that they simply slide back as the tissue heals. Local hunters use spears and machetes on the frog rather than their hands, which tells you the claws work.

24. The Iberian ribbed newt stabs you with its own ribs

Along each flank of the Iberian ribbed newt is a row of orange warts. They mark the tips of its ribs, which are unusually long and sharp. When attacked, the newt flattens, arches its back and swings its ribs forward from about 27 degrees to 92, forcing the tips out through the skin as a row of spines. At the same moment, its skin pours out a milky toxin that coats the exposed bone. A predator’s mouth gets stabbed and dosed in one motion.

There are no permanent holes. The ribs pierce fresh skin every time and it heals over without infection, thanks to the antimicrobial peptides amphibians carry in their skin. The newt shows no sign of poisoning itself, ever.

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06 · Jamming the Signal

The last group does not fight the predator’s body. It fights the predator’s senses, with clicks, glow, ink, fog and, in one case, several gallons of something we would rather not describe.

25. The tiger moth jams bat sonar

Most tiger moths click at bats to say they taste bad. Bertholdia trigona, a small pink and cream moth from the American Southwest, clicks to lie. It buckles a pair of ridged plates on its thorax so fast that it produces up to 4,500 ultrasonic clicks per second, flooding the bat’s echo window with noise at exactly the moment the bat needs a clean return to judge distance. Bats attacking the moths miss, veer off or abort the attack. Silence the moth’s clickers and the bats catch it fine.

The elegant proof was that the bats never learned anything. They failed from the first trial, which rules out a taste warning and leaves only jamming. It was the first confirmed case of one animal jamming another’s sonar, and bats have since been found lengthening their final approach call to fight back.

26. The vampire squid throws glowing fog

Vampyroteuthis infernalis, the vampire squid from hell, lives in the oxygen-starved dark 600 to 900 meters down, is neither squid nor octopus, and is too slow to outrun anything. It also has no ink. What it has instead is light. Under mild threat it flips its webbed arms up over its body like an inverted umbrella, showing spines and flashing the photophores on its arm tips. Under real threat, those arm tips release a viscous mucus loaded with glowing particles, a luminous cloud that hangs in the water for up to ten minutes while the animal slips away into black.

It can also shed an arm tip and grow it back. And for all the name, it feeds on marine snow, drifting on the sticky filaments it trails through the water. The vampire from hell eats dandruff.

27. The Motyxia millipede glows to say it is full of cyanide

In the Sierra Nevada of California there are blind millipedes that glow greenish blue at night. They cannot see the glow themselves, so it was never a signal for each other. In 2011 a team set out 300 clay millipedes in the mountains, half painted with glow-in-the-dark pigment, and by morning the dark ones had been attacked twice as often, mostly by rodents. The glow is a warning, and what it is warning about is hydrogen cyanide, which the millipede releases from pores along its sides.

The best guess is that the light started as a side effect of coping with heat and oxidative stress in dry mountain nights, and only later got recruited as a label. Most of biology is old parts finding new jobs.

28. The sea hare blinds a lobster’s nose

A sea hare is a soft slug the size of a loaf of bread with nothing to hide behind. Attacked by a spiny lobster, it fires two glands at once: a purple ink made from the pigment of the red algae it eats, and a white secretion called opaline that thickens on contact with water. For a long time everyone assumed the ink was a smokescreen. It is closer to a sensory attack. The opaline physically coats the lobster’s antennules and blocks the pores it smells with, and the ink carries chemicals that mimic food, so the lobster stops attacking and starts trying to eat the water.

Sticky cellulose paste applied to a lobster’s antennae works almost as well as the real thing, which is how the researchers knew the trick was mechanical. The lobster is not frightened off. It just cannot find the sea hare any more.

29. The dwarf sperm whale inks like a squid

Kogia, the dwarf and pygmy sperm whales, are small, slow, shy animals a few meters long that hunt squid in the deep and are rarely seen alive. They also carry a sac in the lower intestine holding several liters of a dark reddish brown fluid. When startled by a shark or a boat, the whale voids it in a cloud that can spread across a hundred square meters of water, then hides inside the cloud or slips out the far side, exactly the way a squid uses ink.

So a whale that eats squid for a living has independently arrived at the squid’s best trick. Kogias also have a pale mark behind the eye that looks like a gill slit and a small underslung jaw, which together make them look a little like sharks from the side. Whether that is mimicry or coincidence, nobody has managed to test.

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The argument never ends

Every one of these is a solution to the same problem, and none of them are the final answer, because the predators are evolving too. Bats that hunt jamming moths have started lengthening their final approach call. A snake in Colombia can eat young golden poison frogs. Hornets will find a way. This is the part of nature we find most beautiful: not the armor or the poison, but the fact that the argument never ends.

If any of this made you want more, our stories on the Spider-Man lizard, the firehawks of Australia and twelve animals too weird for fiction are good next steps, and The World’s Most Astonishing Natural Wonders is the long version of the world these animals live in.

Questions people ask

What is the most powerful defense mechanism in the animal kingdom?

It depends on what you mean by powerful. For raw force, the diabolical ironclad beetle survives about 39,000 times its own weight. For chemistry, the golden poison frog carries the most potent toxin. For reliability, the hagfish has never been filmed losing to a shark. We would argue for the bombardier beetle, which combines chemistry, engineering and aim in an animal the size of a fingernail.

Which animals shoot blood from their eyes?

Several species of horned lizard in the genus Phrynosoma, best documented in the Texas horned lizard and the regal horned lizard. They do it almost exclusively at dogs, foxes and coyotes, whose mouths react badly to a chemical in the blood, and rarely at birds or snakes.

Do any animals really explode to defend themselves?

Yes. The exploding ant Colobopsis explodens of Borneo ruptures its own body to spray a toxic glue on intruders, and old workers of the termite Neocapritermes taracua carry crystal backpacks that mix with their saliva into a toxic droplet when they burst. Both die in the process, which is why it only makes sense in a colony.

What is the only venomous primate?

The slow loris. It secretes an oil from a gland on the inside of each arm, licks it to mix it with saliva, and delivers it in a bite. Recent research suggests it uses the venom mainly against other slow lorises.

Which animal has the strongest natural armor?

By weight, the diabolical ironclad beetle. By material, the scaly-foot snail, which builds iron sulfide into its shell and foot plates and is the only animal known to do so. The pangolin’s keratin scales are the most effective against large predators, since lions routinely give up on a curled pangolin.

Photographs are used under Creative Commons licenses and credited in each caption. Click any photo for the original.

Edited by Ben VanderVeen · About Moss & Fog