From poison dart frogs to hagfish slime: 20 animal defenses

Frogs in the family Dendrobatidae are known as poison dart frogs or poison arrow frogs because the toxin exuded by their skin was used by humans to poison the tips of arrows. Most are also brightly colored to warn predators that they are dangerous to eat. Dart frogs are widely kept as pets, which is perfectly safe: They are not poisonous in captivity because the toxin derives from the insects they eat in the wild.

Venom and poison are not the same: Poison makes you sick if you bite the animal, and venom makes you sick if the animal bites you. The primary function of venom is to disable the snake’s prey but it can also serve as a defense against predators. Possibly the most dangerous venomous snake is the inland taipan of Australia, which has the most toxic venom and injects the largest amount with each bite.

Squid ink is more than an ingredient for pasta dishes: It’s an incredibly clever defense. A squid will squirt out a cloud of ink when being chased by a predator. This not only makes it harder for predators to see the squid, it may even fool them into biting at a glob of ink, thinking it’s the tasty creature they’re hunting.

Many insects use an irritating chemical called benzoquinone as a defense against predators, but bombardier beetles take this to the next level. They combine ingredients to produce it inside their bodies at the moment of use, and the chemical reaction heats almost to the boiling point and provides the pressure to eject a spray from their abdomen.

The hagfish is unusual in many ways, including its lack of a jaw and backbone, but most of all for its unique and uniquely gross defense. When it’s attacked or just stressed out, special glands produce about a teaspoon of slime that instantly expands in size 10,000 times. Even a shark will gag and spit the hagfish out and go look for a less slimy meal.

There’s a less fancy way to expel something repulsive as a defense: just throw up. The nestlings of the Eurasian roller upchuck noxious orange vomit when disturbed. Like the dart frog’s poison, it’s thought to contain chemicals derived from the insects in its diet, and experiments show that it’s distasteful to potential predators.

Sea anemones have stinging tentacles that they use to capture prey. The clownfish is immune to their toxin and lives among them, safe from predators. It’s not a one-way relationship, though: The clownfish pays back in several ways, including providing nutrients and helping provide oxygen, aerating the water with its swimming motions.

All species of armadillo have a shell made of hard bony plates covered with a layer of keratin that provides a tough barrier to predators. The three-banded armadillo takes this defense a step further: It’s the only species that can roll up into a ball with its head and legs tucked inside. When they’re rolling up, the shell snaps shut on their assailant, providing an additional deterrent.

Many animals defend themselves by looking like another animal that predators don’t want to mess with. The robber fly doesn’t have a sting, but it looks like a bumblebee, so insect-eating creatures leave it alone.

Looking like something else can also be a different kind of defense strategy: If predators can’t see you, they won’t know you’re there. Stick insects are found all over the world and have evolved to look like astonishingly precise imitations of the vegetation they live among. Some even add to the disguise with their behavior by gently waving like a leaf in the wind.

Evolving to look exactly like one other animal works, but what if you could imitate different animals depending on the situation? That’s what the mimic octopus can do. It’s been observed transforming to look like at least 15 other kinds of sea life from venomous sea snakes and lionfish, to flatfish camouflaged against the ocean floor.

Imitating the way another animal looks isn’t the only kind of mimicry that animals use as a defense. The burrowing owl lives in ground squirrel burrows, which are also frequented by rattlesnakes. They can produce a hiss that sounds like a rattlesnake’s rattle that frightens intruders away.

The Spanish ribbed newt has a unique, bizarre defense that sounds like it must hurt itself as much as it hurts its attacker: It pushes its own sharp-pointed ribs through its skin. On top of that, like most amphibians its skin secretes a poisonous substance, so any predator that tries to eat it gets a mouthful of toxic spines.

When a giant Japanese hornet invades their nest, Japanese honeybees gather around it in a tight ball and begin to vibrate their wings, generating heat and carbon dioxide. They’ve evolved the ability to withstand the resulting temperature of 46 degrees Celsius that’s enough to kill the hornet.

In a number of species of mammals, hair has evolved into stiff, pointed spikes. Hedgehogs add to this defense by rolling into a tight ball completely covered with spines, protecting their head and soft underparts. When the predator drops the spiky ball, the spines also serve as a shock absorber to cushion the hedgehog’s fall.

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Many types of lizards can lose their tail when attacked and later grow it back. It may wiggle for a few moments after detaching, distracting the predator. If the lizard is bitten on the tail by a venomous snake, this prevents the venom from reaching the rest of their body.

When disturbed, a hognose snake will first put on a display of attacking, but if that doesn’t work, it will pretend to die—writhing as if in pain and ending up flat on its back with its mouth open and no signs that it’s breathing, emitting a foul-smelling liquid. This convincing display may persuade predators that it’s not safe to eat.

The killdeer feigns injury to lure predators away from its nestlings. Fluttering along the ground as if its wing is broken, it looks like easy prey, so the attacker is drawn away from the eggs or helpless youngsters.

Snakes aren’t the only animals that produce venom, and biting isn’t the only way to use it. The platypus, one of only two egg-laying mammals on the planet, is also one of the few venomous mammals. Male platypuses have glands in their abdomen that produce the venom and a hollow spur on their hind legs to deliver it.

The Texas horned lizard is well camouflaged in its environment by its mottled skin, but if that doesn’t work, it’s got plenty of other strategies to try. First, it turns its side to the predator to show it what it’s getting into—a long body lined with spines—then, it puffs itself up to look more threatening. If that’s not enough, it squirts a jet of blood out of its eyes that contains noxious substances derived from its diet of insects.