8. TELESCOPIC TENTACLES

The [snail’s] tentacles are as expressive as a mule’s ears,
giving an appearance of listless enjoyment when they hang
down, and an immense alertness if they are rigid, as happens
when the snail is on a march.

— ERNEST INGERSOLL, “In a Snailery,” 1881

WHEN MY SNAIL was active, its muscular head and foot were extended outside its shell, but at the slightest hint of a disturbance, it quickly withdrew them into the shell’s largest, outermost whorl. Its soft body, containing the vital organs—a lung, a heart, and a gastrointestinal system—was connected to its shell by an internal mantle, which also provided space for a water reservoir. It could store about one-twelfth its weight in water and thus, camel-like, survive stretches of dry weather.

About half of my snail’s respiration occurred through its skin, and the other half through a breathing pore—a little hole on its right side below its head. Called a pneumostome, this pore allows air exchange by diffusion, opening infrequently, maybe four times a minute, more or less, depending on the snail’s activity. As warm-blooded creatures, or homeotherms, we humans have to maintain a constant body temperature, but my cold-blooded poikilotherm snail’s temperature matched that of its changing environment. Thus it could get by on half the calories needed by a similarly sized mammal.

My snail was equipped with two pairs of tentacles: the lower pair were a quarter of an inch in length, while the upper pair were nearly half an inch long, with eyes at the tips. The snail could instantly retract its eyes through these hollow tentacles, which themselves retracted just as quickly into its head. “The first striking peculiarity [of the snail] is that the animal has got its eyes on the points of its largest horns,” exclaimed Oliver Goldsmith in 1774 in A History of the Earth and Animated Nature. And at the end of the nineteenth century, in The Dawn of Reason, James Weir explained more precisely that “the snail carries its eyes in telescopic watchtowers.”

When my snail was foraging for food or grazing on a mushroom, its tentacles quivered and twitched continuously. They stretched toward desirable smells but were instantly retracted from anything the least bit offensive. The snail could move its tentacles individually in nearly any direction up to a ninety-degree angle, sweeping them slowly back and forth and up and around, just as a boat under way in the dark swings its searchlights about to look for navigational marks.

While we humans have five senses, relying most heavily on vision to find our way, a snail relies almost entirely on just three senses: smell, taste, and touch, with smell being the most critical. My snail could not hear anything at all; it lived in a world of silence. Its “sight” was highly limited—just a general awareness of dark and light to help with orientation. Bright light might warn of a hotter, drier, and more challenging environment; dark suggested safer, cooler, more humid conditions. A sudden shadow might alert it to a predator.

It was its tentacles—which hold smell and taste receptors—that gave my snail its look of intelligence and purpose. So critical are they to a snail’s survival that, if injured, they can be regrown, just as a starfish can regrow an arm. In an article titled “In the Realm of the Chemical,” David H. Freedman explains:

The land snail . . . devotes about half its . . . brain to taste and smell affairs. It divides the job neatly between its two pairs of [tentacles]: one [upper] pair is waved in the air to pick up smells, while the second [lower] pair is dipped tongue-style into promising substances as a final check before ingestion.

Using the taste buds on its lower tentacles, my snail could distinguish between salty, bitter, and sweet flavors. The thousands of chemoreceptor cells along its upper tentacles were similar to those inside a human nose. Snails “see” the world through smell, the way many insects do, and they can detect aromas from a few airborne molecules.

In its native habitat, my snail determined the source of a scent and the distance from which it wafted based on wind speed and direction. There was no woodsy fragrance blowing through my room, and the snail, especially while it lived in the pot of violets, must have been surprised by the kaleidoscope of unfamiliar smells, the scent of humans, human food, tea, soap, paper, and ink.

Unlike the human nose, infamous for its secretions, the noselike tentacles of a snail are the only mucus-free part of its body. And compared to the stationary, side-by-side nostrils of a human, the snail’s two independent tentacle-noses give it a kind of stereoscopic sense of smell. I imagined a crowd of humans with smell receptors completely covering their arms, walking down the main street of a town. As they passed coffee shops, bakeries, and restaurants, their arms would wave wildly toward the aromas. Perhaps restaurant critics so endowed could, with the wave of an arm, report not just on their own entrée but also on those of other diners at nearby tables.

Though the snail had a sophisticated method of scent tracking, I wondered how it experienced a life so devoid of sight and sound. In its native woods, my snail could not see the moss over which it glided or even the plants it climbed. It could not see the trees, nor the stars overhead. It could not hear birdsong at daybreak, nor the midnight howls of coyotes. It could not even see or hear its own kin, let alone a predator. It simply smelled and tasted and touched its world.

The closest I could come to understanding the snail’s experience of its surroundings was in reading Helen Keller’s portrayal of the richness of smell and touch from her own human experience in The World I Live In:

I am not sure whether touch or smell tells me the most about the world. Everywhere the river of touch is joined by the brooks of odor-perception . . .

. . . Touch sensations are permanent and definite. Odors deviate and are fugitive, changing in their shades, degrees, and location. There is something else in odor which gives me a sense of distance. I should call it horizon—the line where odor and fancy meet at the farthest limit of scent.

I wondered if my snail was aware of a scent “horizon” and how far the odor of a mushroom could float through the air. A snail’s navigation is complex, based on ever-changing odors, sources of darkness and light, a tactile sense of air movement, and, through the touch receptors on its single body-foot, a response to vibrations and types of terrain. This was how my snail mapped the wild woods from which it came, as well as the crate beneath the pot of violets, and the terrarium.

I COMBED THROUGH SCIENTIFIC gastropod literature, eager to know more about my companion. I learned that snails are extremely sensitive to the ingestion of toxic substances from pollution and to changes in environmental conditions, such as temperature, moisture, wind, and vibration. I could relate to this, as my dysfunctional autonomic nervous system made me sensitive to these things as well.

Since I was unable to tolerate most drugs, my doctor prescribed treatments at such minute doses that a pharmacist said he felt as if he were dispensing medication for a mouse. My body’s temperature regulation no longer worked. One moment I was chilled, and the next too hot; this made life as a cold-blooded poikilotherm seem appealing. Before my illness, I had slept like a log with no window shades drawn; now my room had to be pitch black at night. The sound of the telephone sent a tsunamilike shock wave coursing through me, so I kept the ringer turned off. I could listen only to music that was slow and continuous; anything with individually punctuated notes was too jarring. This restricted my entertainment to the calm of Gregorian chants at a barely audible level. I wondered if the snail could sense the vibrations through the air, and what the Benedictine monks would think of singing to a gastropod.