One part, a dozen jobs
What Is a Tail For?
A tail can be a rudder, a balance pole, a fifth leg, a fly swat, a blanket or a shout across a field.
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Step 1 of 5
In water, a tail is the engine.
A fish sweeps its tail side to side and a whale sweeps its up and down, but both are doing the same thing: pushing water backwards, which pushes the animal forwards.
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Step 2 of 5
On a branch, it is a balance pole.
A squirrel or a cat running along something narrow flicks its tail the opposite way to any wobble. Throwing weight one way turns the body back the other — the same trick a tightrope walker uses.
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Step 3 of 5
Sometimes it is a fifth limb.
A monkey can hang from a gripping tail. A kangaroo props on its tail like a third leg and even pushes with it. In those animals the tail carries real weight.
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Step 4 of 5
Often it is a message.
A dog's tail, a deer's white flash, a cat's flick — these are signals other animals read from a distance, where a sound would give away where everybody is.
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Step 5 of 5
It can be a swat, or a blanket.
A horse or a cow uses its tail on flies all day. A fox curls its tail over its nose in the snow and breathes through it, so the cold air is warmed before it reaches the lungs.
You have the leftovers of a tail. A few small fused bones sit at the base of your spine, where a tail used to be.
The short version
A tail is whatever the animal needs most — an engine, a balance pole, a limb, a signal or a blanket.
Try it yourself
Walk along a line on the floor with your arms out, then with them folded. Your arms were doing the tail's job.
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