Why do animals have tails?

This month, I’ve been thinking a lot about a question I’ve gotten several times from blog readers and on nature walks: specifically, why do animals have tails? Although I’ve heard this more often from younger children, plenty of adults also find it to be a head-scratcher when they really think about it. Tails, after all, are such a key part of how we think about animals. We humans don’t have tails, but many of the fellow critters with which we share the Earth have tails of all shapes and sizes. So why is that?

Although a lot of other blogs and online sources take a pretty simplistic approach to answering this question, I think there’s actually more to it than just what animals use their tails for. Exploring the world of animal tails from a more in-depth perspective, there is a lot we can learn from a scientific standpoint that makes other things in nature easier to understand. So I figured I’d spend this Naturalist Answers post answering this question from different perspectives to answer this question in a better way.

What are tails?

First, an important question that I don’t see other nature blogs talking about, which has a big influence on how we answer the bigger mystery of why animals have tails. What exactly do we mean by a tail? As any Beginner Naturalist might learn if they pick up a good book on plants, many parts of different plants that look the same are actually totally different things. For example, what look like petals on a sunflower are actually themselves tiny flowers that have adapted to perform the function of an individual flower’s petal. Or sharp, pointy thorns on one plant might look like spikes on another, but one came from a leaf bud, and the other from the tissue of the stem. We animals are not so different: things that may look the same or perform similar functions might not actually be the same thing. Horns and antlers, for instance, are made of very different stuff, even if they do similar things for their owners!

Read More: What’s the Difference Between Horns and Antlers?

While the tails of things like dogs and cats, or crocodiles and squirrels and birds are all the same sort of thing, an extension of their spinal cord, the tail of a scorpion or even of some fish is something very different, even if it does something similar. Perhaps the biggest divide among what we might call tails in the animal kingdom is the gap between vertebrates, those animals that have a spine, and invertebrates, those that don’t. While the majority of animals on Earth are invertebrates (more specifically, insects!), the wildlife we’re most familiar with, and who we think about when we think of tails, are the vertebrates. These include mammals, reptiles, birds, amphibians, and fish, most of whom definitely do have one kind of tail or other.

Read More: 8 Insect Orders that Every Nature Lover Should Know

Tails among invertebrates are not really tails in a technical sense, but they might serve that kind of purpose. Arachnids like spiders and scorpions, and insects both have abdomens, which are, for lack of a better word, their butts. They contain their guts, and stick out behind them, and are thus kind of like a tail. For animals like hymenopterans, the large order of insects that includes wasps and ants, females will have a stinger that resembles a tail, but is actually a modification of an egg-laying organ called an ovipositor. Meanwhile many crustaceans like horseshoe crabs, lobsters, crayfish, and amphipods have an extension from their rear-end called a telson which functions in many ways like a vertebrate tail. Scorpion’s famous tails are a great example of a very sophisticated telson.

The tails of more familiar wildlife like vertebrates are actually part of their spine, and stick out the back of their body along its centerline. These tails are thought to have first occurred in ancient fish, whose spinal columns extended into a rear appendage that they used for swimming. Fascinatingly, most modern day fish (with the exception of “living fossils” like paddlefish and sturgeons) actually have tails that are just made of fin tissue (more like cartilage), and which don’t include their spine, so they are different than the tail of, say, a fox or a tiger. With the exception of adult anurans (frogs and toads) and apes like humans, almost all tetrapods, which are the land-based animal descendants of many ancient fish, have tails. In tetrapods, the tail consists of the parts of the spine which extend out behind the pelvis. The human tail, which actually develops briefly in the womb and then is reabsorbed into the body, is only evident in the existence of a coccyx or tailbone.

While the tails of ancient fishes no doubt served them the way these flexible fins help their modern relatives get around, they also helped many land-based animals solve any number of problems. As we’ll learn in the next section, even though tails may have started off in the water, they do many fantastic things on land and in the air, too! So let’s dig into some of the reasons why animals have tails.

11 Reasons Why Animals Have Tails

1. Just Because

First and foremost, some animals just have tails. Those tails might not necessarily be super useful, but they can just stick around as a holdover from a time when they played an important role in that animal’s life history. This might not sound like a serious answer, but it’s actually one of the most scientifically interesting reasons for animals to have tails.

Read More: What is a Life History?

As I mentioned earlier, the aquatic ancestors of land-dwelling tetrapods had tails for swimming in the water. Sometimes, when a trait is super important, it just sticks around in a species’ descendants even if it isn’t useful. For example, pinky toes don’t do much for us, but we still have them! For some animals, having a tail may just be a mark of their ancient past, when a tail was a big part of their lives. When a group of organisms all has a trait that they got from their ancestors, it’s called synapomorphy. This is one of the least intuitive but simplest reasons why animals have tails: because their predecessors did!

2. Swimming (Aquatic Locomotion)

Plenty of animals other than fish have “real” tails and still use them for their original purpose: swimming through the water. You can find lots of examples among tetrapods that, after adapting to walking or crawling around on land, returned to the water. This includes some extremely cool animals, for example crocodilians (gharials, caimans, alligators, crocodiles), sirenians (manatees and dugongs), cetaceans (dolphins and whales), and sea snakes (Hydrophiinae). Interestingly, despite not having any limbs, snakes are still also tetrapods, but they lost their limbs over time since they weren’t useful for their particular lifestyle.

All of these swimmers make use of a strong, muscular tail with vertebrate in the middle of it. These powerful tails are their primary way of getting around in and under the water, and are an essential part of their lives. Swimming tails might be used to help predators chase prey, or slow grazers like manatees move between patches of attractive vegetation. Alternatively, they can allow an animal to “high-tail it” and escape falling prey to something else!

3. Balance

My first answer to the question of why animals have tails is typically that it helps animals maintain their balance. Watching a squirrel or a housecat run down a tree branch or make rapid turns and pivots while running across the ground shows how tails make them more agile and balanced. In an extreme case, cheetahs are famous for using their tails to help them turn quickly on their incredible sprints in pursuit of gazelles and other fast-moving, agile prey.

Beyond balancing for climbing and sharp turns, other animals use their tails simply to balance their bodies. Sauropod dinosaurs, the famously long-necked, giant herbivores like Brachiosaurus and Apatosaurus, probably needed their long, muscular tails to counterbalance their huge necks. This makes me think of the counterweights on construction cranes, which keep them from toppling over despite the long “arm” extending from their fronts.

4. Signaling (Communication)

For many animals, tails are a convenient “flag” for signaling, as they can stick up above the animal’s body and can be visible to others while they’re walking around or engaged in other activities. Anyone who has owned or spent time around dogs will be inherently familiar with the use of tails for communication. While dogs certainly have facial expressions and lots of other ways to express themselves, their tails can really say a lot! An upright tail often signals alertness and engagement with someone else, while a wagging tail famously conveys excitement, often in a positive way.

Cats’ tails will also show whether they are intrigued, scared, feeling social, or agitated. White-tailed deer use their tails to signal danger to their others nearby, and will flash their bright colors if fleeing a predator. Those bright colors might also serve a defensive function, but more on that later.

5. Aerial Steering and Braking

Bats and birds are two modern-day vertebrates that mastered the skies, and their tails play an important role in flight. While their wings provide the power for forward movement and the lift to keep them aloft, their tails are essential rudders and brakes. This can help them change their speed in the air, slow down or stop to land, and change directions rapidly if needed. For predatory animals, these deployable tail flaps gave them the agility to pursue prey in search of food, while they gave other animals the ability to escape when needed. While some pterasaurs, ancient, extinct flying reptiles, had tails, many did not, and they seem to have had a smaller role in flight.

6. Grabbing stuff

Famously, new world monkeys (those originating in the American tropics) have strong, flexible tails that can wrap around objects and perform a grabbing function like an extra hand. These prehensile tails are a huge advantage for animals dwelling in trees, letting them hang with all four limbs free to grab food, scratch, or get hold of the next branch. Spider monkeys (genus Ateles) are among the most famous examples of animals with prehensile, grabby tails.

Of course, monkeys shouldn’t have all the credit. Other animals also have prehensile tails, and without exception are extremely cool critters. In the reptile world, chameleons in Africa, the Middle East, and Southern Asia and Europe can use their tails as an extra support point when they are moving their feet between branches. Tree pangolins (Phataginus tricuspis) and Tamandua anteaters are both examples of cool tropical animals that use their prehensile tails to get around in dense rainforests. Closer to home for some, the North American opossum has a bare tail which similarly serves a grabby purpose.

Read More: All About the Opossum

7. Swatting Insects

Biting insects are a major problem for most land mammals, especially during certain times of year. Beyond just a nuisance, they can weaken animals in great numbers and more often transmit potentially harmful diseases. Tails are extremely useful tool for swatting away these pests, especially for animals that might be an easy target or not have another way of getting rid of them. Large herbivores like ungulates (hoofed mammals), elephants, and rhinoceroses all need their tails for dealing with these bugs since they make an easy target. Being large and occupying more open areas, they could otherwise get swarmed! Tails’ usefulness as a mosquito deterrent has been the subject of scientific studies. These found that animals invest significant energy in tail-swatting, but that the generated air movement is enough to deter half of mosquitoes even if they miss!

8. Fat and Water Storage

When I was in fourth grade, I got an African fat-tailed gecko (Hemitheconyx caudicinctus) as a pet. I can remember reading all about these neat animals in books from the library and on the internet. Among the coolest and most unexpected facts I came across was why they had such chubby tails: they use them for storing excess nutrients and also water, almost like a camel’s hump! In the years since, I discovered that quite a few other reptiles do this to a lesser extent, including alligators. These extra fat stores can help animals endure leaner times when food is hard to come by, especially in places with long winters or dry seasons. Some mammals can also make use of this strategy (although less dramatically than the reptiles), for example beavers and, surprisingly, Tasmanian devils!

8. Making Noise

Tails are also excellent tools for producing sounds. I’ve lost count of the number of times I’ve been startled by a sudden CRACK of a beaver tail striking the water while I explored a swamp or canoed in a lake or pond. Without my knowing, a beaver had spotted me, a potential threat, and used its flat tail to warn others in the area of the unwanted intrusion. For an animal whose vocalizations are restricted to little grunts and chirps, a beaver’s tail offers a great and far-carrying line of communication that is quick and efficient. Another famous example of a noise-making tail is a rattlesnake’s rattle. Although snakes can’t vocalize beyond a hiss, a few shakes of a rattlesnake’s tail is enough to get across a serious warning that few experienced animals ignore.

9. Warmth

If you’ve ever seen a hibernating chipmunk or a cat sleeping in a cold room, you may be aware of another under-recognized reason for animal tails: warmth! Many animals in cold regions have large, fluffy tails, which they can use the warm themselves when resting. The extra fur on a poofy tail can make a great insulator to buffer the feet, legs, or face from the cold when an animal is lying down. I don’t think I’ve looked at a picture of a cozily sleeping fox with its tail all curled up and not felt a little jealous.

Read More: How Do Plants and Animals Survive the Winter?

10. A Disposable Decoy

Although they perform a great many functions, tails for many organisms are a bit less important than other parts of the body. For example, I’ve seen dogs lose parts of their tails to injury, or to expectations of their appearance, and live perfectly happy, normal lives. Injuries to the limbs, head, or body might be fatal or severely affect an animal’s life, but injuries to the tail might not pose such a huge threat. As an extension of this, some animals have actually designed their tails to make an effective decoy when under attack.

This makes a lot of sense if you think about it: when attacked by a larger predator, the intuitive reaction for many animals is to, well, turn tail and run! If the tail is the closest thing to an attacking predator, and not the most essential part of the body, it makes sense that it might be worth sacrificing if it means getting out alive. Many lizard species thus have tails with special “breakpoints” that allow them to easily come off when the animal is in danger or under attack. An attacking predator is suddenly faced with a still-moving, detached tail—a big distraction!—that might hold its attention long enough for the prey to get away. Many species that lose their tails in this way can grow part most of all of their old tail in time, although it may come back looking a little funny.

Scientists call the way that lizards can “cut off” their own tail when it’s seized by a predator autotomy, meaning “self-cutting”. This allows them to—pun not intended—cut their losses and get out of a bad situation that may have cost them their lives.

11. Extra “Leg” or Kickstand

Although extremely uncommon, one last major reason why animals have tails is worth mentioning. A small group of animals, specifically kangaroos and their relatives (family Macropodidae) can use their tail to directly support their body weight on the ground. In other words, their thick, robust tails can act as a kickstand, or, in some cases, an extra (fifth) leg! Kangaroos in particular are famously the only animals capable of what scientists call pentapedal locomotion, walking on five “legs”!

Read More: The 15 Weirdest Animals in Australia

Although it also plays a big role in balance, kangaroo tails rely heavily on this extra leg when fighting. Male kangaroos will often box with one another when fighting over mates, and use their strong tails to support themselves when kicking at one another with both legs.

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