Thursday, May 7, 2020

Trailing the Snail

From guest blogger, Tonya Smith, MN
After walking with my eyes glued to the ground looking for fungus after a rain,  I happened to look up at chest level and spotted this snail feasting on the fungi on a dead tree limb.  My close inspection including a camera lens inches away from it did not in any way interrupt it’s meal. It looks like a Whitelip Snail but we would need measurements and pictures of the aperture of the shell looking for teeth to be sure.

Snails are graceful animals that rely on touch and smell since their vision is limited and they have no ability to hear. Using their muscular foot (yes, one foot) lubricated with mucus, land snails glide along a variety of surfaces found in the woods.  If you have ever seen a snail crawling on a glass window or aquarium, you would see their movement is powered by succeeding waves of muscular contractions that move down the ventral of the foot. Wikipedia   The mucus is secreted from a gland on the foot  reduces friction,and the risk of injury from sharp objects including the sharp edge of a razor blade as in this video.   But snails do have their limits. They will not cross copper since it reacts with their slime giving them a shock.

Snails have four tentacles with eyes at the tip of their longer pair of tentacles. Their vision is limited to recognizing light and dark and knowing when to find protective cover from the sun which is critical to their survival. Snails are usually active at night, on rainy days or when humidity is high. All four of its tentacles are equipped with olfactory sensors. These noses-on-stalks allow snails to sample biochemical compounds in the air and on the ground. Snails' acute sense of smell can detect fungi from a distance, home in on a rotten log, smell other snails’ slime, and find their way back to a preferred resting location. They can swivel their tentacles independently and more importantly, regrow them if they get bitten off - a great survival mechanism.

Land snails eat a variety of foods including living or dead plants, rotting wood, algae, and fungi as you see here. Some may also dine on animal scat, tree sap, and dead animals.  A few species are carnivores, feasting on earthworms, roundworms, other snails and their eggs. In the circle of life, land snails are prey for a wide variety of reptiles, small mammals, birds, and insect larvae. Snails eat by scraping surfaces with a specialized structure called a radula. It is a long strip of tissue like a wood rasp with hundreds of replaceable teeth. The radula is drawn back and forth over a surface, scraping food into the mouth.  Here is a video clip of the radula in action.

Since snails are hermaphroditic, they can both “father” and “mother” offspring. When a pair of snails mate, they can fertilize each other, and each may lay a cluster of eggs. Land snails usually lay their eggs in clusters in a small hole they dig into damp soil.  Before hatching, a baby snail grows a protoconch, the embryonic shell which is colorless and very soft. Check out these newly hatched snails in motion.  You won't need slow motion.

The mantle is where new shell material is formed. It starts out soft like the material of the protoconch then expands the shell and hardens it. The protoconch it was born with ends up in the center spiral of the shell when the snail is fully grown. As a snail matures, the number of whorls or spirals which its shell has increases and the rings can be used to approximate the age of the snail. A calcium rich diet is important to the health of a snail’s shell. The baby snail starts this healthy diet by eating what’s left of its egg shell.

Now what about that slimy slime trail? According to Ken Hotopp, an expert on land snails of the eastern U.S. snail slime is “a marvel of chemistry,” and all slime is not the same. It varies in its chemical makeup, acidity, and thickness. Foot slime is thinner, allowing for a smooth flowing movement, but it gets tacky when snails stop, enabling them to attach to a surface, even upside down. The slime that protects snails from drying out has anti-fungal and anti-bacterial properties.

A thick slime is exuded when snails feel threatened, which makes them distasteful to things that want to eat them. Some species have a slime visible under ultraviolet light, probably serving as a warning to predators that see in the ultraviolet portion of the spectrum. Slime can also attract predators. The carnivorous snail, Haplotrema concavum, hunts other snails by following slime trails. (Snail Slime is Sublime)

Snails sense when they’re upside down thanks to equilibrium organs called statocysts. These are capsules filled with liquid and calcareous grains (statoliths) floating within. As soon as the snail moves or changes its position, inertia has the statoliths float against the statocyst's wall helping the snail sense gravity.

How do snails tolerate the cold and hot weather? Snails can hibernate during the colder months of the year by covering their bodies with a thin layer of mucus preventing them from drying out. In extreme dry periods of the summer, sometimes snails also do a similar process to survive called estivation. These methods of adapting are probably one of the reasons they have survived for millions of years. Snails are one of the slowest creatures on the Earth - just behind the sloth which wins the award for the slowest in the world.

On your mark, get set, SLOW! Yes, a snail race has been a tradition in Congham, England. 215 snails competed in the 2019 World Snail Racing Championship with a final 13 competing for the world champion title. Sammy covered the 13 inch course in 2 min and 13 seconds. The world record of two minutes is held by Archie. 

Missouri has more than 100 terrestrial snails. At least 12 land snails are Species of Conservation Concern in Missouri. I was very surprised to learn on a global level, there are more species of land snails and slugs than all the land vertebrates (amphibians, reptiles, mammals, and birds) combined.

In Maine, a snail became a patient’s greatest comfort. This particular land snail became a companion to author, Elisabeth Tova Bailey, as she coped with her own serious bed ridden illness. A friend brought Elisabeth a pot of flowers that also contained a wild snail the friend had plucked from the ground. Her book titled The Sound of a Wild Snail Eating describes her observations of this snail which lived in a terrarium next to her bed.  Two creative quotes from her book:
“With its mysterious, fluid movement, the snail was the quintessential tai chi master.  The life of a snail is as full of tasty food, comfortable beds of sorts, and a mix of pleasant and not-so-pleasant adventures as that of anyone I know”
One little snail sparked my interest to learn more than I anticipated. I discover more moving at a snail’s pace on my walks in nature. Well, maybe I’ll move a little faster than the snail speed of several inches a second. Just in case you have missed it, there is a snail emoji. Use it kindly.

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*You can download Land Snails and Slugs of Missouri by Chris Barnhart

Pocket Guide to the Land Snails of Kansas