Aposematic Coloration: Nature’s Brightly Colored Warning Signs

A close-up image of a flamboyant cuttlefish sitting on the ocean floor

Many animal species use their coloration to blend in with the surrounding environment, concealing themselves from both predators and prey. For instance, plenty of ocean animals are able to blend in with the sandy ocean floor or rocky coral reefs.

But sometimes, you see a creature like the flamboyant cuttlefish (shown above). This aptly-named animal doesn’t blend in with anything, and you’d think its bright colors would just attract would-be predators.

These colors do stand out to predators, but that’s actually advantageous for the flamboyant cuttlefish. Its muscle tissue is highly toxic, and the bright colors serve as a warning to would-be predators. This is something known as aposematic coloration.

What Is Aposematic Coloration?

A close-up image of a fire salamander curled up on a mossy rock

The name “aposematism” comes from two Greek words: “apo,” meaning “away,” and “sematic,” meaning “sign.” That effectively sums up the purpose of the coloring — to predators, it’s a sign to stay away.

Aposematism as a whole doesn’t have to include coloration. It simply involves an animal using any perceivable characteristic to warn predators that it is venomous, poisonous, or otherwise unpleasant to eat. For example, the rattling sound that rattlesnakes make is a form of aposematism.

Some scientists even believe that humans historically used a form of aposematism as well. Researchers have hypothesized that human scent stood out to larger predators to warn them that early humans could defend themselves with weapons.

When animals use colors as a form of aposematism, those colors are typically very bright. If an animal has a pattern, the pattern almost always involves very high contrast. After all, the coloration must be (1) striking enough to catch the attention of a predator and (2) distinctive enough that the predator will remember it.

Most animals with aposematic coloring are red, yellow, black, white, or a combination of these colors. The animal pictured above is a fire salamander. You can see why its high-contrast coloration would stand out to predators.

The fire salamander secretes samandarin, a toxic alkaloid that makes vertebrates hyperventilate and gives them painful convulsions. If a predator experiences these symptoms after trying to eat a fire salamander, they almost certainly will remember the distinctive color and stay away in the future!

Examples of Aposematic Coloration Around the World

Because so many animals are dull in color in order to camouflage, seeing a brightly colored one can be exciting. Here are some of the most distinctive animals with aposematic coloration.

1. Strawberry Poison Frog (Oophaga pumilio)

A close-up image of a strawberry poison frog sitting on a yellow leaf

This colorful creature (sometimes called the blue jeans poison frog) is native to Central America. Its vivid coloring warns predators that it secretes a specific alkaloid poison called pumiliotoxin 251D. If a predator eats a strawberry poison frog or attempts to eat it, it may become paralyzed, experience convulsions, and even die.

Interestingly enough, this frog doesn’t actually produce pumiliotoxin 251D on its own. Rather, it obtains it from mites and other insects it eats and then isolates the compound. Other species of poison frogs do the same. When kept in captivity, they don’t secrete the toxin, as their diets don’t include the exact insects they eat in the wild.

2. Monarch Butterfly (Danaus plexipuss)

A close-up image of a monarch butterfly perched on pink and yellow flowers

The monarch butterfly is famous for its annual migration across North America. This butterfly species’ unique coloration has endeared it to people around the globe, but for would-be predators, it serves a very different purpose. Although the richly-colored orange on its wings might not look quite as jarring as bright red or bright yellow, the high-contrast pattern warns predators that it’s toxic and tastes incredibly bitter.

Like the strawberry poison frog, the monarch gets its toxins from the food that it eats. The caterpillars feed on milkweed plants. These plants produce toxic compounds called glycosides, so they are toxic to most animals. The monarch caterpillars have evolved to be immune to the toxins, and as they feast on milkweed, they accumulate the glycosides in their bodies.

If a bird or other animal eats a monarch caterpillar or butterfly, it will become temporarily sick, but it usually won’t die. However, it will remember the butterfly’s vivid coloration and stay away in the future.

3. Red Eft (Notophthalmus viridescens)

A red eft walks along a damp forest floor

The red eft might look like a small adult lizard, but it’s actually the juvenile form of the eastern newt. It can be found across much of eastern North America. Red efts have especially striking aposematic coloration — their bodies are bright orange, and they have small, bright red spots on their backs.

Predators are fortunate that this warning is hard to miss. Red efts produce tetrodotoxin, the same poison found in pufferfish. At least to humans, tetrodotoxin is about 1200 times more toxic than cyanide. Fortunately, you won’t be affected if you simply pick up a red eft — you’d have to eat one to be poisoned! Still, they should be left alone in nature, where they belong.

4. Velvet Ant (Mutillidae family)

A close-up image of a female velvet "ant," also called a cow-killer

Despite the name, the velvet ant isn’t an ant at all. It’s a type of parasitoid wasp, and only the females are wingless and look like ants (the males look more like actual wasps). It might look plush and soft, but touching one wouldn’t be a smart move. Females have an excruciatingly painful sting, so velvet ants are also sometimes called “cow killers.”

There are several different species of velvet ants, but fortunately, most are large enough that they can be easily spotted and avoided. The largest species is about ¾ of an inch long.

5. Greater Blue-Ringed Octopus (Hapalochlaena lunulata)

A greater blue-ringed octopus with illuminated, iridescent blue rings on the body

The glowing blue rings on this octopus might be beautiful, but if you see them flashing, stay away! This octopus species is one of the world’s most toxic marine animals. When it needs to warn away a predator, it will flash its blue iridescent rings.

Like the red eft, the greater blue-ringed octopus produces tetrodotoxin. It can release this potent neurotoxin when it bites either a predator or a prey animal. The bite itself is painless to humans, but the very painful effects of tetrodotoxin begin to take effect about 15-30 minutes later.

6. Skunk (Mephitidae family)

A black and white skunk with raised tail walks in a green backyard

You may have heard people talk about taking a bath in tomato juice after being sprayed by a skunk, but that “remedy” is just a myth — experts now recommend a mix of dish soap, hydrogen peroxide, and baking soda. Skunk spray comes from two glands that secrete pungent, sulfur-containing compounds. The smell is unpleasant enough to ward off almost all predators.

Fortunately, because skunks can’t immediately replenish their spray, they will first try to warn a predator. They will puff up, hiss, and stomp their feet. However, they’re also one of the rare mammals exhibiting aposematic coloring — once a potential predator is sprayed, it will remember the high-contrast patterning and stay away.

7. Cinnabar Moth Caterpillar (Tyria jacobaeae)

A close-up image of an orange and black cinnabar moth caterpillar crawling on a flower stem

The cinnabar moth is a beautifully patterned insect with striking red and black markings. Its caterpillar also has highly memorable coloring, as it’s marked with contrasting black and orange bands. These bands warn predators that the caterpillars contain toxic alkaloids, compounds they get from their diet of ragwort.

However, some scientists believe that in this caterpillar’s case, the aposematic coloring can also work as camouflage. Up close, the high-contrast pattern can’t be missed. But researchers have found that when the caterpillar is viewed from a distance, the black and orange colors seem to mix together and form a shade that actually blends in with the background.

8. Ladybug (Coccinellidae family)

A bright red ladybug (or ladybird) walks on a blade of green grass

The ladybug is more properly called a ladybird beetle or a lady beetle, as it’s a beetle and not technically a bug. There are many different species, but most have highly noticeable red wings with black spots.

This conspicuous coloration warns predators that the ladybug’s blood is full of highly toxic alkaloids. If the color alone doesn’t deter a predator, the ladybug can effectively offer a free sample of the poison by secreting a few drops of its toxic blood. In addition to plant alkaloids, ladybug blood also includes pyrazine compounds that smell especially bad.

9. Lionfish (Pterois species)

A close-up image of a lionfish on a vivid blue background

The lionfish is an especially stunning Indo-Pacific fish. But its spines and its high-contrast stripes aren’t just for show. Each of its 18 spines secretes venom that can be fatal. In humans, the venom causes full-body effects including nausea, fever, heart failure, convulsions, and temporary paralysis of limbs.

Despite their highly toxic venom, lionfish are somewhat popular aquarium pets!

10. Honey Badger (Mellivora capensis)

A honey badger surveys its surroundings as it perches up on a rock

The honey badger isn’t brightly colored. However, its patterning is remarkable because it’s the reverse of countershading, an extremely common form of natural camouflage. Countershaded animals have dark upper bodies and light lower bodies, and this pattern is thought to reduce the appearance of shadows, making them less visible to predators and prey.

Honey badgers are the exact opposite. The dorsal side of their body is light, with the ventral side being black. Like the black and white coloring of the skunk, the honey badger’s coloring can warn predators of its incredibly foul-smelling anal gland secretion. A honey badger’s spray can even temporarily blind an attacker!

Aposematism and Batesian Mimicry

A close-up image of a Mexican milk snake on a black background

Aposematism doesn’t only benefit poisonous, venomous, or otherwise unpalatable creatures. Over thousands of years, harmless species have evolved to look like harmful ones. This defense mechanism is known as Batesian mimicry.

The Mexican milk snake (shown above) is a great example of Batesian mimicry. It looks very similar to the Texas coral snake, shown below:

A Texas coral snake slithers along the concrete

Coral snake venom is the second most toxic of any snake in the world. (If you’re wondering, the black mamba holds the record for the most toxic snake venom.)

A Texas coral snake’s bite can be fatal. But if a predator is bitten and lives, it will certainly remember to avoid the snake’s red, black, and yellow bands.

The Mexican milk snake, on the other hand, is completely harmless, and a predator could eat one with no ill effects. However, because the coloration is pretty much indistinguishable from that of a coral snake, predators assume Mexican milk snakes are similarly venomous and avoid them entirely.

Fortunately, there’s a critical difference between the two species that lets humans tell which is venomous. The Mexican milk snake’s red bands are adjacent to the black bands, and the Texas coral snake’s red bands are next to the yellow bands. You might have heard the saying “Red next to black, venom lack. Red next to yellow, kill a fellow.” It’s an easy way to make sure you don’t get the two patterns mixed up!

Aposematism and Müllerian Mimicry

A close-up picture of a bumblebee on a blue flower

Batesian mimicry involves a harmless animal mimicking a harmful one to protect itself from predators. But sometimes, two harmful species share the same (or similar) aposematic coloration. This is known as Müllerian mimicry.

One example of this type of mimicry is the bumblebee. In North America, there are several species of bumblebee — so many that they have formed what researchers have called a “mimicry complex.”

As you may have already been unfortunate enough to find out, bumblebees have a painful sting. If a predator is stung, it’s likely to avoid any bee with similar black and yellow coloration. That way, if a predator has a bad experience with one bumblebee species, it will avoid all species — not just the one that stung it.

Aposematic Coloration Is All Around Us

As you likely saw above, many of the most strikingly colored animals live in tropical regions. But no matter where you are in the world, you’ll almost certainly see aposematic coloration when you look for it. These bright colors are warning signs, but they’re also beautiful to look at. Just be sure to admire them from afar!