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One foot, one shell, no hurry

How Does a Snail Carry Its House?

A snail's shell is not a house it moved into. It grew out of the snail's own back, and it is growing still.

One muscular foot, nolegsSlime to glide on andto grip withA shell that grew fromits own backEyes on stalks thatpull in
Everything a snail needs is attached to it.

  1. Step 1 of 5

    It moves in ripples along one foot.

    A ripple starts at the back It travelsforwards That strip sets down further ahead The nextripple begins

    Underneath is a single flat foot. Waves of muscle run along it from back to front, so a small strip is lifting and reaching while the rest holds still — a conveyor belt made of one muscle.

  2. Step 2 of 5

    The slime is two things at once.

    Pressed slowly Stiff — it gripsPushed hard Runny — it slides

    Press it slowly and the slime is stiff enough to grip. Push it suddenly and it turns runny and slippery. That is how a snail can climb straight up glass and still not slide back down.

  3. Step 3 of 5

    The shell grew with the snail.

    1 Hatches with atiny shell2 Adds new rim atthe opening3 The spiral getswider each turn

    A snail hatches with a tiny shell already on it and adds to the open edge as it grows, curling round and round. The lines you can see are the record of that growth, like tree rings.

  4. Step 4 of 5

    It is made of the same stuff as chalk.

    A hard, banded shell Calcium taken from itsfood

    The shell is mostly calcium, taken from the snail's food and soil. Which is why snails hunt for gritty, chalky places — a snail short of calcium ends up with a thin, easily broken shell.

  5. Step 5 of 5

    The eyes are on stalks, and they retract.

    1 The stalk isstretched out2 Somethingbrushes the tip3 It turns insideout and pullsin

    A garden snail has two long stalks with simple eyes on the tips, and two short ones for smelling and feeling. Touch a stalk and it pulls in on itself, the way a sock turns inside out.

    Snail eyes see light and dark and rough shapes, but almost no detail. Smell and touch matter far more to a snail than sight.

The short version

A snail glides on ripples of one big foot over clever slime, inside a shell it grew itself out of calcium.

Try it yourself

Look at a snail on the inside of a glass jar. You can watch the ripples travel along its foot from underneath.

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