How Do Animals Protect Themselves From Predators?

Have you ever wondered how animals protect themselves from being eaten by other animals? There are a couple of ways that animals can protect themselves from predators. Some animals hide from predators by blending in with plants, tree bark, and leaves around them, like the forest-dwelling rocket frogs and leaf-tailed geckos. Arctic foxes also blend in with the white snow of their arctic tundra habitats (Figure 1A). We call this cryptic coloration, or camouflage.

Other animals are bright and colorful. These animals are often red, yellow, or orange, which helps them stand out from their green or brown surroundings and makes them easy for predators to spot. That seems to make no sense, right? Why would animals want to stand out and risk being eaten? One reason for bright colors is to show predators that they are dangerous to eat! This strategy is called aposematism [1] (Figure 1B).

Warning! I Am Dangerous!

There are several ways that animals can show predators that they are dangerous to eat. First, the animals must have a primary warning signal that predators can either see (think of the bright colors on a monarch butterfly’s wings), smell (think of a skunk’s spray), or hear (think of a rattlesnake’s rattle). Next, the animals will have a secondary defense to signal their distastefulness to predators, usually poisonous chemicals called toxins.

This article will focus on aposematic coloration in animals, which means that color is used as the warning signal. The bright warning colors act as a sign telling predators that the animals have a secondary defense, such as being toxic. This means that these colorful animals can make predators feel sick or die if they are eaten. If a predator survives, it learns to avoid these brightly colored animals in the future. How do animals get their warning colors? As we describe below, they can get their colors from their parents and/or they can get their colors from the foods they eat.

Aposematism From Parents

Just like humans inherit characteristics like the color of our eyes, skin, and hair from our parents, animals can inherit colors from their parents. Some aposematic animals are brightly colored because their parents passed down their bright colors to them. Coral snakes have red, black, and yellow stripes on their bodies, which they inherit from their parents (Figure 1C). They have venom and their bites can be deadly to predators and to humans. Some mammals, like the skunk, also get their warning coloration from their parents. Predators know to avoid skunks and their smelly spray because of their black-and-white striped coloration [2].

You Are What You Eat: Aposematism From Food (And Parents)

Some animals also have warning colors because of what they eat (in combination with what they inherit from their parents). Their foods can give them a bright warning color and provide toxins that make them poisonous to predators. For example, many animals get their bright colors from carotenoids in their foods. Carotenoids are non-toxic yellow, orange, or red colors found in many of the foods that you eat, like carrots, bell peppers, and beetroots. The brightly colored tropical poison dart frog (Figure 1B) gets its color from its parents and from its diet of ants, beetles, and millipedes—which contain carotenoids. In addition to carotenoids, ants and other animals in the poison dart frog’s diet contain toxins that the frog can use to make itself toxic. Ever heard your parents say you will turn into a donut if you eat too many donuts? That is kind of what happens with the poison dart frog’s color and toxicity. If these animals eat more carotenoids or toxins, they become more brightly colored and more toxic.

Carotenoids are also found in weedy plants called milkweeds, which are eaten by the beautiful monarch butterfly. Carotenoids help give monarch butterflies their bright orange wings [3]. Monarch butterflies also eat and store a poisonous chemical called a cardenolide from milkweed. While cardenolides are poisonous to the monarch’s predators, monarchs are protected by a gene they inherit from their parents, which helps them reduce the negative effects of cardenolides. Cardenolides are not delivered in spray, like a skunk, or by a bite, like a snake. Instead, monarch butterflies store toxic cardenolides throughout their bodies, so when they are eaten, the predator also eats these toxins.

Another animal that gets its warning color from carotenoids in its food is the bright aphid. Aphids are yellow or orange sap-sucking bugs that also eat milkweed. They get their color from the milkweed and from their parents. Like monarchs, they can also store cardenolides from the milkweed to make themselves toxic. One predator of the aphid has grown to use the toxins from its prey: the beautiful ladybug. Ladybugs are beetles known for their red wings with black spots. They get their color from their parents and their carotenoid-containing diet of aphids. They get their toxicity from the cardenolides stored in the aphids they eat. Eating more aphids during their larval (immature) stage increases the toxins in their bodies and makes their bodies more red.

What Happens When a Predator Eats a Toxic Animal?

If a bird eats a monarch butterfly, the toxic cardenolides will cause the bird to throw up (Figure 2), since birds do not have protection from these toxins [4]. After the bad experience, the bird learns to avoid eating things that look like the monarch butterfly, including other orange insects. This is an example of an experience called taste aversion. Humans can experience taste aversion, too! Just like birds, after we get sick from eating a certain food, we typically stay away from that food for a while, out of fear that it might make us sick again.

Are Bright Animals Always Toxic?

If an animal shows a warning color and is toxic, that means the animal is honestly signaling its toxicity to predators. Sometimes toxic species will copy each other and present the same warning signal, so that predators learn to avoid both species. For example, in Figure 1C, you may have noticed how similar the viceroy butterfly and monarch butterfly look. These two poisonous species have grown to resemble one another. This is known as Müllerian mimicry.

Not every animal that shows a warning color is toxic, though—some animals have a warning color but are not toxic. Certain non-toxic animals mimic the warning colorations of other animals that are toxic. You may call that cheating! These are called Batesian mimics. Unlike Müllerian mimics, which are honest about their toxicity, Batesian mimics are dishonest. These animals take advantage of predators that avoid the bright colors they have learned to mean danger. Batesian mimics are protected because they look like true aposematic animals. One example is the scarlet kingsnake, which is a mimic of the coral snake in the United States (Figure 1C). These snakes look so similar that Americans have created a rhyme to help people tell the difference between them: “If red touches yellow, you are a dead fellow; if red touches black, you are all right, Jack”. This means that snakes with red and yellow stripes touching are dangerous! [5] Be careful though, because this pattern does not hold for all coral snakes outside of the United States.

Aposematism is All Around You

In summary, aposematism is a way that dangerous prey draw attention to themselves to warn predators not to eat them. If you look outside, you may recognize examples of aposematism all around you, such as ladybugs, bees, and wasps. There are also examples in your own life! Warning road signs are often neon yellow or red, to make the danger clear to drivers. Or think about spicy chips, which are often more boldly colored, along with their packaging (Figure 3). What other examples can you think of? Think deeply about the colors you see all around you and what they are telling you. Be honest, and do not be afraid to be bold and show a little color!

Glossary

Cryptic Coloration: ↑ A way that some animals hide from predators by blending in with their surroundings. Also known as camouflage.

Aposematism: ↑ A defense strategy used against predators, in which a warning signal is paired with a defense mechanism.

Toxin: ↑ A substance that is poisonous and can make animals that eat it feel sick or die.

Carotenoid: ↑ Yellow, orange, or red colors found in vegetables, monarch butterflies, aphids, and ladybugs. They are non-toxic.

Cardenolide: ↑ Poisonous chemical in the milkweed plant that monarch butterflies store to protect themselves from predators.

Taste Aversion: ↑ When a predator has a bad experience eating an animal and learns to avoid eating that animal in the future.

Müllerian Mimic: ↑ A poisonous animal that copies another’s warning signal, so that predators learn to avoid both animals.

Batesian Mimic: ↑ A non-poisonous that animal copies a poisonous animal’s warning signal, so that predators will avoid it, too.

Acknowledgments

We would like to thank Weixin Du for drawing Figure 2. Thank you to Amaya López Gordon and Monique Pipkin for providing feedback on each of the drafts.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.