A Snail on a Sooty Tin Roof
December 2, 2021
Melissa Donahue
Tracks on the roof
This is the view of the roof of the library on the Learning Center Campus. The markings have caused a bit of discussion among the Nature Center's naturalists. Even though it looked as if an alien creature is visiting the library, it soon became clear the truth was far more interesting.
White-lipped Snail
Land snails are responsible for these tracks on the roof! According to the TN Wildlife Resources Agency, there are at least 120 land snail species in middle Tennessee. Fossil records show snails have been on the earth at least a half a billion years. With a life span of 2 – 5 years, it has been discovered snails have a memory, can retain knowledge for weeks to months, and adapt behavior based on that memory.
A snail consists of a hard shell and a soft body. The shell, made mostly of calcium carbonate, is protection for the soft body. It grows with the snail and can provide a place for the snail to hibernate if environmental conditions become unfavorable.
The soft body contains all the organs and orifices the snail needs to live. As you can see from the above diagram there are a lot of organs in a little space. The snail has a lung and breaths through a respiratory pore as well as the skin. When thirsty, they can sip through the mouth or drink through the skin. The process of drinking through the skin is called "foot drinking". The snail has both male and female parts, but that subject is for another blog.
Close up of long and short tentacles
Each snail has two sets of tentacles that can regrow if needed. The upper tentacles allow them to experience the wider world. Longer, with a pair of retractable eyes on top, these tentacles wave in the air to pick up smells, moving towards good smells and away from bad. Although they have eyes, snails rely on smell, taste, and touch rather than sight to experience the world. The second set of tentacles are smaller. These tentacles are used to dip into potential food sources for a final check before eating. Using these small tentacles a snail can distinguish between salty, bitter, and sweet. The tentacles are the only mucus free section of a snail’s body.
Most people when they think of snails think of slime. Slime (mucus) is used for movement, defense (who wants to eat a mouthful of slime?), temperature regulation, courting, mating, and egg protection. A snail produces at least five types of mucus cells. One type of slime allows the snail to move. Moving on a bed of slime, which they have changed from a solid to a liquid disrupting friction, a snail can move a few inches per minute. Navigation relies on odors, dark and light and touch receptors on the body/foot. These touch receptors respond to vibration and the types of terrain. Snails seem to have a home base, often in the leaf litter, and are active mostly at night. They will venture out for food, often returning to the same spot each morning, although, if necessary, they will change their sleeping spots. Juvenile snails tend to go further afield than older snails.
Close up of Snail Markings
It seems these odd trails were caused by a snail eating. Snails are scavengers and eat what they can find, observations indicate their favorite food to be mushrooms. Although they may prefer mushrooms, these scavengers find the mold on the roof an easy meal. A snail has a sword like tongue and an immense number of very sharp teeth The teeth are pointed inward, with 80 rows of 33 teeth. The teeth are positioned on a multitoothed ribbon called a radula, so when teeth wear down a new row takes its place. Land snails do not chew their food, but instead scrape it, using their radula.
Snail Markings and Ruler
So...back to the mysterious markings on the roof of the building. The snails are enjoying a meal of sooty mold. The mystery starts with the woolly aphids on the hackberry trees around the building. The aphids suck the sap out of the leaves and secrete a substance called honeydew which drops onto the roof and mold grows. As a result, a black mold covers the roof of our library. The snails then eat the sooty (black) mold. We were intrigued by the patterns of these snails and decided to take a closer look. Using their many teeth and sword like tongue the snails make passes along the roof. There are about 25 licks per pass and 14 passes in one inch. After a little math it was determined that the snails tongue covered 13.5 inches for every inch the snail moved forward, or the snail’s tongue moves about 14 times faster than the rest of the snail. Please contact me if you want more information.
A special thanks to Will Chamberlain for all his help and math skills. And his contribution of this haiku.
"Spiral coiled stone home,
Slow it glides on self-paved paths--
Silent in the night."
(Wi Cha)
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