Lives of Woodland Snails

Imagine having the time to watch the life of a woodland snail.  That’s what happened to Elizabeth Tova Bailey when she was felled by a mysterious neurological illness that put her flat on her back.  She could not move without pain, and so she was tended by a caregiver in a studio apartment.

Then, one day a friend brought her a pot of purple field violets that she had dug up in a New England forest.  It also held a woodland snail.  After finding the hungry snail had chewed square holes in her letters during nighttime forays out of the pot, she put withered flowers in a dish beneath it and watched from her bed as the snail crept down the side of the pot and ate the blossoms.

“I could hear it eating.  The sound was of someone very small munching celery continuously,” she writes in her charming and informative little book The Sound of a Wild Snail Eating. Thus began her sedentary adventures with this intriguing creature.

It reminded me of my own encounter with a woodland snail many years ago when our three boys were children.  On a hot, dry day in early August, I spotted one climbing a leaf.  When I looked at it with my hand lens, it ignored me and kept moving instead of withdrawing into its shell as snails usually do.

Fascinated by what I thought was an unusually sociable snail, I plucked the leaf and carried it and the snail home to show our sons.  When I put it down on the kitchen table, it quickly moved to the edge of the leaf and on to the table.  Then I put my forefinger in front of it, and it climbed up on it.  I could feel the suction from its pinpoint-sized mouth as it “tasted” or rasped my skin, a painless feeling similar to being licked by a cat.  I also watched it excreting slime from a gland behind its mouth, which enabled it to glide smoothly over my finger.

Moving one inch every ten seconds, it circled my finger several times before moving to its tip and extending its upper pair of tentacles toward my second finger.  It stretched the front part of its body across the gap and its head landed on my middle finger.  At the same time, its shell dangled in the gap and its foot or tail remained on my forefinger.  But it quickly pulled shell and foot on to my middle finger and performed the maneuver twice more to reach my little finger.

From tip to tip, its body measured two inches and its pair of larger tentacles with primitive eyes at its end was a half-inch long.  Below them, near its mouth, were two small tentacles that are sensitive touch organs.

When I put it back on the leaf, it withdrew into its shell. Still, our son Dave persuaded me to let it stay until my husband Bruce returned from work and could photograph it.  Bruce arrived two hours later, and I told him about my adventure.

As if on cue, the snail emerged suddenly from its shell and resumed its exploration of my fingers while Bruce took pictures.  What a ham! Afterwards, I put it outside on a leaf and off it went.

Later, I did some research on woodland snails and learned that they usually estivate on hot, dry days by drawing into their shells and sealing themselves off with a mucus door called an epiphragm. That same mucus it had secreted on my fingers has a high acid content that allows it to dissolve the calcium carbonate the snail must ingest to keep its shell strong.

A woodland snail obtains calcium by eating decaying leaves and wood, fungi, algae on wood and rocks, sap, animal scats, carcasses, other snails, bones, antlers, and soil.  They also absorb it through the soles of their feet.  Calcium carbonate not only forms their shell structure, but also helps in “fluid regulation, cell wall function, muscle contraction, and egg laying,” according to an excellent web site on Pennsylvania land snails, written by Ken Hotopp, Principal of Appalachian Conservation Biology, and edited by Tim Pearce, head of the Carnegie Museum of Natural History’s Section of Mollusks.

Unfortunately, acid rain reduces forest soil calcium, which, in turn can reduce snail numbers by as much as 80%. Decaying sugar maple logs are particularly rich in calcium.  So too are calcium-rich limestone outcrops.  Maybe that’s why we don’t see as many woodland snails on our acidic mountain land as are in our limestone-rich valleys.

In captivity, a  woodland snail eats lime and paper to obtain calcium, which brings me back to Bailey’s adventures with what she later discovered was a white-lipped forest snail (Neohelix albolabris), a denizen of humid woodlands from Georgia to Ontario and west to the Mississippi River.

“Despite its small size,” she writes, “the snail was a fearless and tireless explorer… With its mysterious, fluid movement, the snail was the quintessential tai chi master.”

Bailey’s caregiver found an empty rectangular glass aquarium and fashioned a terrarium for the snail with goldthread, partridgeberry, checkerberry, mosses, polypody ferns, a rotting birch log and a piece of bark festooned with multicolored lichens, all organic materials on which a snail feeds.  Every week it also ate one slice of Portobello mushroom. A mussel shell held water.

Like my snail, Bailey’s snail “seemed to defy physics.  It moved over the very tips of mosses without bending them, and it could travel straight up the stem of a fern and then continue upside down along the fern’s underside.” But, in reality, it is its incredibly adhesive mucus that allows such feats.

She also watched it grooming itself  as it arched “its neck over the curved edge of its own shell and cleaned the rim carefully with its mouth…Its curiosity and grace pulled me further into its peaceful and solitary world,” she writes.

Snails are mollusks in the Class Gastropoda, meaning “stomach foot,” which refers to their method of locomotion. The word “snail” is Old English and comes from the German “schnecke,” a spiral-shaped yeast bun.

A radula or chitonous organ in its mouth is covered with tiny teeth that point inward so it can grasp its food.  Its soft body has a lung, heart, and gastrointestinal system which is connected to its shell by a mantle that stores up to 1/12^th of its weight in water.  It breathes partly through its skin and partly through a breathing pore, a little hole on the right side below its head called a “pneumostome.” Next to it is an anal pore for excreting undigested food in the shape of a tiny, twisted rope.

A woodland snail has three senses — smell, taste and touch.  Their rudimentary eyes can only distinguish light from dark, and it can’t hear at all. Its tentacles are smell and taste receptors and can be regrown if they are injured.  If its shell is broken, its mantle, the membrane-like organ around the snail’s aperture or opening from whence the snail emerges, builds new shell material.

Nearly 1/3 of a snail’s daily energy goes into mucus production, which is filled with antioxidants and regenerative properties.  It even has material useful in treating acne.  Mostly important for maintaining a snail’s skin and allowing it to move, it also is used to deter predators.  When attacked, it exudes copious amounts which confuse or even smother its enemies.  Such enemies are legion — beetles and their larvae, flies, nematodes, ants, mites, spiders, millipedes, shrews, mice, amphibians, reptiles and birds, particularly ground foragers such as ruffed grouse, wild turkey, thrushes and blackbirds.

Even larger snails, such as the gray-foot lancetooth (Haplotrema concavum), a widespread Pennsylvania species, eat smaller snails.

One of the more interesting predator/prey relationships is that between land snails and Cychrine beetles, the latter evolving narrower heads to pull snails from their shells, while snails have evolved more obstructed apertures.

In winter, a woodland snail stops eating, makes a burrow with soil and leaves, and withdraws deep into its shell, its sealed opening facing upward.  Its heart rate slows to a few beats a minute and its oxygen to 1/50^th of its usual intake.

Land snails mate in late spring, early summer, or fall, depending on the weather.  Because most Pennsylvania land snails are hermaphrodites, meaning they have male and female reproductive organs, each snail produces eggs and sperm.  Some snails can fertilize themselves.  That’s what Bailey’s snail did.

Some snail families, after circling each other and exchanging tentacle touches and before mating, shoot tiny darts of calcium carbonate into each other.  Researchers believe these are reproductive hormones that increase paternity odds.

Then they embrace in a spiral direction and mate by exchanging sperm, which is often in spermatophore packages.  The donor’s penis transfers it into the receiver’s vagina, which, in both cases, is an opening called the “atrium” on the right side of the snail’s head.  Once inside, the spermatophore releases the sperm and sperm and eggs meet in a fertilization chamber.

Shortly thereafter, depending on the species, one to dozens of eggs is laid in a damp area.  Bailey’s snail laid some on top of the ground and some buried in the soil.

“Under a microscope the translucent egg-envelopes present a beautiful appearance, being studded with glistening crystals of diamonds,” wrote Ernest Ingersoll “In a Snailery” back in 1881 and quoted by Bailey in her exhaustive study of woodland snail natural history.

Bailey may be the first person to have recorded observations of a snail tending its eggs.  Her snail produced 118 offspring, losing none, as it would have in the wild, to predators.

Eventually, Bailey recovered and returned home, releasing not only her original snail but also its offspring.

Worldwide, 35,000 land snails have been named, but tens of thousands are still not identified.  In Pennsylvania, malacologists have discovered 120 land snail species of both shelled animals and slugs, although very little is known about the life spans and movements of most species.  But one study in Illinois of the broad-banded forestsnail (Allogonia profunda), a species also living in Pennsylvania, found that it moved back and forth between its winter hibernation spot and its home in pieces of log mold during its four-year life span.

All these small lives are virtually unknown to us.  And, as Bailey and I have discovered, even individuals in a species can behave differently.  I never could figure out why the woodland snail I found was out on such a hot, dry day.

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For more information:  Consult the Carnegie Museum of Natural History’s website at http://www.carnegiemnh.org/mollusks/palandsnails/

Read Bailey’s book, but if you find it at the library, as I did, be forewarned that it has been classified as a memoir by librarians, instead of a natural history book.  It has a several-page bibliography of books and articles about land snails, both recent and historical. Here’s the trailer from YouTube.