By Charlotte Owen
Tails come in all sorts of different shapes and sizes. If you’re a vertebrate, you’ve probably got one – though humans (and all great apes) are notable exceptions. So why do animals have tails, what are they used for, and why don’t we have one?
Fish have tail fins to help propel them through the water. They can be forked, rounded, pointed or flattened depending on swimming style but all fish have vertical tail fins, and they generate forward thrust by moving them from side-to-side.
Basking shark © Alexander Mustard/2020VISION
Tadpoles swim in a similar fashion but their tails disappear during metamorphosis. Adult frogs don’t need tails on land, and they swim using their long, powerful back legs.
Whales and dolphins (cetaceans) have horizontal tail fins, and they swim by moving them up and down. Individual whales can sometimes be identified by the unique shape and pattern of their tail fins.
Seals have tails too but they are small and often obscured by their hind flippers, which do all the hard work while swimming.
Most birds have tails ending in long flight feathers called rectrices. The name comes from the Latin for ‘helmsman’ or ‘one who directs’ and the tail feathers play an important role in steering, stabilising and braking during flight. They also help the bird balance while perched, and for flightless birds like the ostrich they provide stability while sprinting.
Blue tit © Nigel Symington
Bats have tails too. In most species they are incorporated into the wing membrane that stretches between their hind legs but some bats (the free-tailed and mouse-tailed bats) have tails that extend beyond the edge of the membrane, and they use their tail to feel their way as they back into crevices.
Pipistrelle bat © Barry Yates
Any animal that climbs, sprints or leaps over large distances will have a long tail that acts as a counterbalance and rudder. In general, the faster the animal the longer the tail – and without it, they would stumble and fall.
Red squirrel © Peter Cairns/2020VISION
Treecreepers and woodpeckers have specialised tail feathers that are stiffened to provide balance and support while climbing.
Great spotted woodpecker © Peter Brooks
A prehensile tail acts like a fifth limb, gripping onto branches and stems to help the animal climb or save them from falling. The harvest mouse is the only native British mammal with a truly prehensile tail, perfect for climbing through the stalk layer.
Harvest mouse © Derek Middleton
Sea horses also have prehensile tails, which they use to anchor themselves in place. While most tails have a round cross-section, the seahorse has a square tail and this unusual shape provides a stronger grip.
© John Newman
In some bird species, the males have extra-long or colourful tail feathers for use in courtship. The peacock is the most obvious example: males that are stronger and fitter can produce and maintain a larger, showier tail, and this is how females select the best mate.
Horses and other hoofed mammals have a tail perfectly designed to swish away any pesky flies that might try to bite them.
Keeping cool (or warm)
Rats can keep cool by dilating the blood vessels in their long, almost-hairless tails, which have a large surface area perfect for heat loss. When it gets colder, the blood vessels constrict so that body heat is conserved.
Brown © rat Gillian Day
Animals with furry tails like foxes, squirrels and dormice, can wrap up warm by tucking their tail around their head and body to sleep.
Red fox © Alan Humphries
Many animals display their emotions or intentions by the position of their tail, and body language is an important form of communication – especially for foxes and other canids.
Rabbits and deer can signal danger with a flash of their white tail, while beavers use their tails to slap the water.
Defence and escape
Common lizards and slow worms can shed their tails to escape a predator. This is called autotomy, or self-amputation. Once detached, the tail keeps wriggling long enough to distract the attacker while the lizard scurries to safety. The tail will eventually grow back but shedding it is always a last resort, because it also plays a role in locomotion, reproductive success and energy storage (via fat deposits).
Common lizard © Sean Stones
All of the above
Most tails are multi-functional, providing a combination of benefits.
Why don’t humans have tails?
Once upon a time, we did – but it’s a case of use it or lose it. When our ancient ancestors started walking on two legs, they no longer needed a tail for balance; in fact, it was probably more of a hindrance, so humans (and all apes) evolved to be tailless. Interestingly though, human embryos still grow a tail. It’s quite distinct for the first month or so of gestation but after that, the tail disappears and we are left with a tail bone but nothing to show for it.