The Sound of a Wild Snail Eating (5 page)

9. MARVELOUS SPIRALS

And seeing the snaile, which every where doth rome,
Carrying his owne house still, still is at home.

— J
OHN
D
ONNE
, from “To Sir Henry Wotton” (1572 – 1631)

E
VEN WHEN MY
snail was asleep, I loved to gaze at the beautiful spiral of its shell. It was a tiny, brilliant accomplishment of architecture, and because the radius of the spiral increases exponentially as it progresses, it fits the definition of a logarithmic or an equiangular spiral. Also known as the marvelous spiral, it accounts for the sound of the sea that one hears when an empty shell is lifted to the ear: outside noise enters the curving chamber and echoes back and forth, jumbling into a continuous surflike tone.

In 1905, G. A. Frank Knight delivered a lecture to the Perthshire Society of Natural Science in which he noted that

the whole subject of convolution in the mollusca is one of extreme interest, and has excited the enquiries of eminent scientists . . . The animal, with unerring certainty, will mould for itself a habitation, which . . . will be finished with an absolutely perfect devotion to geometrical curves, proportion, and principles . . . How infinitely varied the series of curves may be, and how wide is the scope granted . . . [but] the law of “the spire of the logarithm” must be strictly adhered to.

In most languages, the word for “snail” refers to its spiral shape: in the Native American language Wabanaki, the term is
Wiwilimeq,
for “spiraling water creature.” Giovanni Francesco Angelita, an Italian scholar, wrote an essay in 1607 titled “On the Snail and That It Should Be the Example for Human Life.” He praises the creature’s thoughtful pace and good morals and credits it with inspiring everything spiral, from the invention of drill bits to Europe’s most famous staircases.

As a snail grows, its mantle secretes material at the shell opening, thus lengthening and widening its house by increments to keep up with its expanding body size. A snail’s shell is “part and parcel of the animal itself,” points out the nineteenth-century naturalist Searles Wood, as quoted in
British Conchology.
And Edgar Allan Poe, in an odd leap from his usual macabre genre, comments in the preface to
The Conchologist’s First Book
in 1839 that “the
relation
of the animal and shell, with their dependence upon each other, is a radically important consideration in the examination of either.”

My snail’s shell had five and a half turns or whorls around its center starting point. I could see the past growth lines, and its final shell opening was elegantly rounded off with a wide, creamy lip. Was this curved lip a way to strengthen the shell edge? Perhaps it was a sort of built-in gutter system. I would learn, soon enough, that this detail proved, irrevocably, my snail’s maturity.

In Italo Calvino’s book
Cosmicomics,
in a story titled “The Spiral,” the molluscan narrator expounds on the art of shell making and reflects on what it is like to be part shell. But it was the gastropod narrator in Elizabeth Bishop’s poem “Giant Snail” that is so enchanted with its own shell that it made me want my own:

Ah, but I know my shell is beautiful, and high, and glazed, and shining. I know it well, although I have not seen it. Its curled white lip is of the finest enamel. Inside, it is as smooth as silk, and I, I fill it to perfection.

The whorls of a snail shell lean asymmetrically out from the center. My snail’s shell was dextral, with a right-side opening, as is most common. However, some snails are sinistral, with a left-side opening. In his Perthshire Society lecture, G. A. Frank Knight takes us inside for an architectural tour:

If we imagine the interior of the shell to be a spiral staircase, then, as we ascend a
dextral
mollusc, the “axis” . . . of the stair would always be at our left hand, and similarly, if the mollusc be
sinistral,
the stair up into its interior would always curve round the axis on the right hand.

Spiral direction has an impact on relationships; a snail must find a mate of its species with a matching shell.

If a snail’s shell gets injured, a repair can be made quickly. New shell material is secreted by the mantle, and where there was once a crack, a scar appears, looking much like a skin scar. Even a missing shell section can be replaced. Oliver Goldsmith described this in 1774:

Sometimes these animals are crushed seemingly to pieces, and, to all appearance, utterly destroyed; yet still they set themselves to work, and, in a few days, mend all their numerous breaches . . . to the re-establishment of the ruined habitation. But all the junctures are very easily seen, for they have a fresher colour than the rest; and the whole shell, in some measure, resembles an old coat patched with new pieces.

In an article titled “Shell Fish: Their Ways and Works,” published in 1852, George Johnson praises the snail’s shell as “an edifice rivalling, nay exceeding, in complexity yet order of details and perfection of elaborate finish, the finest palaces ever constructed by man!” Johnson’s “elaborate finish” probably referred to the colorful shiny shells of the tropics. My woodland snail’s shell, however, though beautifully and perfectly formed, was an earthy color with a modest matte finish. It was better described by the Mandarin Chinese words for “humble abode,” which are “wö jū” or a
, literally meaning “snail’s house.”

Reminding me of a rolled-up sleeping bag—the kind I had once strapped atop a backpack—my snail’s shell was a brilliant solution to a life of wanderlust. And there was a further benefit. In the third or fourth century BC, the Athenian poet Philemon observed, “How ingenious an animal is a snail . . . When it falls in with a bad neighbor it takes up its house, and moves off.”

U
NLIKE THE STURDY EXTERNAL
shell of my snail, my supporting structure was internal. But the bones that made up the skeleton deep within me were losing their density at a rapid rate, and there was little I or my doctors could do to halt the problem. My status as a vertebrate was literally dissolving. I would eventually become a spineless, soft-bodied creature, more like a gastropod than a mammal. And unless my armpits could secrete shell material, I would be more slug- than snail-like.

I observed my snail’s spiral shell from the outside, but what was it like to live inside such a shape? Just a month before the onset of my illness, I had visited the Guggenheim Museum in New York. Halfway down the rotunda’s spiraling interior, I stopped. It was dizzying to look up as the floors curved around and above me and equally so to look down to the ground level far below. Now I tried to imagine, were I as large in proportion to the Guggenheim as the snail to its shell, what it would be like to have my head stick out the main entrance below and my body wind all the way up the spiraling floor.

10. SECRET RECIPES

My wide wake shines, now it is growing dark.
I leave a lovely opalescent ribbon: I know this.

— E
LIZABETH
B
ISHOP
, from “Giant Snail,” 1969

H
UNDREDS OF MILLIONS
of years ago, by chance, some marine snails evolved certain traits that allowed them to colonize land. To survive the challenges of a dry terrestrial habitat, they had to keep their bodies moist. While my mammalian ancestors evolved dry skin to prevent dehydration, my snail’s gastropod clan went in a different direction, perfecting and luxuriating in the sticky thickness of slime, or mucus. While
Homo sapiens
have internal mucus, and more of it than we realize, it’s the extravagant nature of the gastropod to be completely coated externally.

While slime can certainly be disgusting, it hadn’t occurred to me that it might be interesting. So many times I had come in from gardening to wash up, dissolving the dirt instantly with water and soap, only to find that the patches of slime from inadvertent encounters with hidden slugs—the less aesthetic relatives of my elegant snail—remained impervious, sticking to my hands like glue. It took a pumice stone or even four-hundred-grit sandpaper to get the stuff off.

Slugs, despite what one might think, given their naked look, do not predate snails on the evolutionary tree but were once snails that evolved over time to be shellless. Without a shell to tote around, they can change their shape more easily than a snail, thus squeezing into smaller crevices.

The biologists C. David Rollo and William G. Wellington once commented with amusement on their gastropod subjects: “A bag of cold water that cannot even move unless it leaks should not be able to survive outside a bog.” And yet, thanks to their protective slime, terrestrial gastropods have thrived.

Slime is the sticky essence of a gastropod’s soul, the medium for everything in its life: locomotion, defense, healing, courting, mating, and egg protection. Nearly one-third of my snail’s daily energy went into slime production. And rather than making a single batch of “all-purpose” slime, my snail had a species-specific recipe for each of these needs and for different parts of its body. It could adjust the ingredients, just as a good cook would, to meet a particular occasion. And in a catastrophic accident in which a snail is squashed, it can release a flood of lifesaving, medicinal mucus packed with antioxidants and regenerative properties.

Skimming a chapter titled “Molecular Biomechanics of Molluscan Mucous Secretions” by the zoologist Mark Denny in
The Mollusca,
I came across a powerfully alliterative phrase that stuck in my head: “the macromolecular architecture of molluscan mucus.” The technical details were beyond me, but clearly the phrase had to do with how the stuff holds itself together—how a quantity of water is controlled by a bit of salt and a protein-sugar. Denny points out admiringly that “if stirred with a rotating rod . . . [mollusk mucus] recoils when the stirring is stopped, and . . . has sufficient tensile strength to self-siphon out of a beaker.”

My snail secreted a special kind of slime for locomotion, called pedal mucus, over which it traveled. While its ability to glide over a patch of moss appeared effortless, when it went up the glass side of the terrarium, I could see bands of minute ripples moving across the underside of its foot. These ripples momentarily turned the mucus from solid to liquid, disrupting friction and allowing the snail to advance at a speed of a few inches per minute. Its single-footed method of travel was far more ancient than my own bipedal ambulation or that of my quadruped dog.

“Upon this slime, as upon a kind of carpet . . . [the snail] proceeds,“ wrote Oliver Goldsmith. The zoologist T. H. Huxley, author of
Practical Biology,
commented in 1902 that “the wave-like contractions” of a snail’s foot are “so delicately adjusted . . . that the creature can crawl with ease and comfort over a knife-edged surface.”

Slime travel has intrigued some innovative researchers in the Netherlands. Hoping to improve the comfort level of colonoscopies, they are designing a small robot that can travel snail-like through the mucus-coated intestines of humans. I wondered what other snail traits might inspire further biomimicry.

Pedal mucus is an incredible adhesive; it explains my snail’s ability to cross over soft mosses; proceed upside down along a leaf; or sleep, oblivious to gravity, high on the side of the glass terrarium or dangling from the tip of a fern frond. Before the snail’s arrival at my bedside, the concept of ceiling art had absorbed my attention. I would concoct in my mind various methods for safely affixing horizontal images to the white surface above me. Perhaps slime glue was the solution.

The sticking power of slime, in concert with a muscular foot, creates a creature of Olympic caliber, as documented by E. Sandford in the
Zoologist: A Monthly Journal of Natural History
in 1886:

Experiments to Test the Strength of Snails

Perceiving a Common Snail . . . crawling up the window-blind one evening, it occurred to me that I would try [to discover] what weight it could draw after it . . . Accordingly I attached to its shell four reels of cotton which happened to lie on the table . . . I then weighed the entire load and found it to be two ounces and a quarter, while the snail itself weighed only a quarter of an ounce. Thus it was able to lift perpendicularly nine times its own weight! I then made an experiment with another and somewhat larger snail, which weighed about one-third of an ounce, the load being . . . drawn in a horizontal position on the table. Reels of cotton to the number of twelve were fastened to it, with the addition of a pair of scissors, a screwdriver, a key, and a knife, weighing altogether seventeen ounces, or fifty-one times the weight of the snail. The same snail, on being placed on the ceiling, was able to travel with four ounces suspended from its shell. I next tried it on a piece of common thread, suspended and hanging loose, with another snail of its own weight, which it carried up the thread with apparent ease. After this I tried it on a single horse-hair strained in a horizontal position, but it had then enough to do to crawl over this narrow bridge without a load.

Where was the Society for the Prevention of Cruelty to Animals? Apparently it was not paying close attention to snails. Perhaps the larger snail’s refusal to carry a burden over the single horsehair was due, at least in part, to sheer exhaustion after participating in so many experiments.

Snails will often reuse their own or another snail’s trail in order to save on slime production. By detecting pheromones in a trail, they can determine whether it leads to foe, friend, or potential mate. Some terrestrial snails even “gallop” by picking up the front of their foot and leaping forward, leaving behind a dotted slime trail. This may save on slime use or possibly outwit a predator. If frightened, one snail species will lift itself up on its posterior and speed-glide eighteen inches per minute.

The idea of being coated from head to toe with such a slippery, sticky substance was unsettling to me. I thought that my snail would feel an equal aversion to sunning itself on a hot, sandy beach. Evolution has led to our contrasting skin anatomies and, as a result, to our opposite fears.