How To Build Little Doors Inside Your Shell: The Secrets of Snail Carpentry : Krulwich Wonders... Snails getting ready for winter are natural carpenters. They construct doors, or maybe you'd call them walls, inside their shells. They do this without hammers, nails or cement. Instead, they use their foot — and of course, their favorite material, mucus. Welcome to the ingenious world of snail construction.

How To Build Little Doors Inside Your Shell: The Secrets of Snail Carpentry

"I am going to withdraw from the world," says a snail in Hans Christian Andersen's tale The Snail and the Rosebush. "Nothing that happens there is any concern of mine."

Snail 1
Robert Krulwich/NPR

In the fall, snails get cold. They sense the days getting shorter so they prepare for what's coming. You'd expect them to, of course, but it's how they do it that surprised me. Until I read Elizabeth Tova Bailey's new snail book, I hadn't a clue. They begin by slipping into their shells ...

Robert Krulwich/NPR
In the fall snails sense the days getting shorter so they prepare for what's coming.
Robert Krulwich/NPR

... head in, foot last. And then they start building doors. Not doors of wood or stone or soil. Being snails, they choose mucus.

The goopy ooze they use for locomotion is also a sticky attractant, so using their feet (sorry, "foot"), they pick up bits of stone, leaf and soil, and, according to the Rev. William Kirby, who described this back in 1835, using that foot "as a shovel to make its mortar ... [as] a trowel to spread it evenly," they build a door. They seal the entrance to their shell in a manner something like this ...

Snail 2
Robert Krulwich/NPR

Snail scholars call this door an "epiphragm." Depending on the species and the harshness of the winter, a snail might make it thick or thin, or in some cases, it may make several of them, as described by Ernest Ingersoll in his 1881 essay, "In a Snailery."

"Withdrawing into the shell, the animal throws across the aperture a film of slimy mucus, which hardens as tight as a miniature drum-head. As the weather becomes colder, the creature draws itself a little farther in, and makes another 'epiphragm' and so on until ... the animal [is] sleeping snugly coiled in the deepest recesses of his domicile."

I imagine if you could X-ray a snail shell, you might see — if it's an especially cold winter — a series of doors within doors within doors ...

Snail 3
Robert Krulwich/NPR

These slime plates, according to the anonymous author of "Snails and Their Houses" (1888), "act on the principle of double windows, enclosing a layer of air between each pair, and so effectually protecting [the snail] from the cold."

Breathing? Eating? Pooping?

So how then, does an enclosed snail eat, defecate or breathe? The answer is: It slows itself way down. Whether dormant or hibernating, it stops eating, its heart rate goes to barely a beat or two a minute and, writes Elisabeth Tova Bailey, "its oxygen intake diminishes to one-fiftieth of its active use." As for defecation, I'm guessing some things they just live with.

I do worry about suffocation, though. Three doors in, buried in its hard shell, where is the snail to get any oxygen? Well, says Elisabeth, the doors may be porous to air, or "(s)trategically located breathing holes may be incorporated." However they do it, and different snails do it differently, when it starts to rain and snow, the snail is snug, warm and protected. Ready for winter.

Robert Krulwich/NPR
Snail 4
Robert Krulwich/NPR

Then months later, when temperatures rise and the sun stays longer in the sky, the snail somehow senses springtime coming, breaks down its doors and steps out for a stretch and another season of crawling, eating and, with a little luck, loving. It all happens slowly, of course, but it happens year after year. Doors are built. Doors are de-doored, the dance goes on, snail-style.


Elisabeth Tova Bailey's book is The Sound of a Wild Snail Eating. I've blogged about it before (when I learned that snails have teeth). The citations to old books in my post, I got from her. In her chapter about hibernation, she notes that making these mucus doors relieves snails of the chore of migrating — and then she tries to imagine a hibernating snail. What a concept! That gets her thinking about a French poet, Jacques Prevert, whose "Song of the Snails on Their Way to A Funeral" tells the story of "two snails that plan to attend a service for an autumn leaf that has fallen to the ground. They travel toward their destination, and when they finally arrive for the funeral, spring has come and all is happy again." Ah, sometimes things just work out.