A land snail, as the name implies, is a terrestrial snail that does not live in water. It is different from a slug only because it has a shell. Most land snails have lungs and breathe air. They often live in damp or soggy habitats, such as moss or wet soil.
Most of a snail’s body is protected inside its shell. Only the head and foot protrude. The strong muscular foot contracts and expands to move a snail along. The foot secretes a mucus that reduces friction and allows the snail to crawl over coarse surfaces. Because the snail rides on this mucus layer, the snail remains uninjured if it crawls over a sharp object – even the edge of a razor blade! Snail mucus also prevents the snail from drying out. The shiny mucus trail a snail leaves behind can often be seen for hours.
Snails move very slowly – at a “snail’s pace.” This rate has actually been studied and measured: 1 mm/second for a typical land snail.
Many land snails have male and female organs and produce sperm and eggs. Despite this, snails mate with other snails to maintain genetic diversity. About one-third of land snails stab potential mates with a sharp, needlelike spear called a love dart. This dart can be one-fifth the length of the snail. Until mating it is hidden in the snail’s body. Mucus on the dart contains a hormone that increases the success of the sperm.
After being punctured (or not) by a love dart, snails maneuver their genital pores close together and exchange sperm. During mating, a snail passes about 5.5 million sperm to its partner (for comparison, human males pass about 200 million to 300 million sperm). Of these sperm, fewer than 1 percent survive. But if a snail has been punctured by a love dart, twice as many sperm survive to fertilize eggs. Because it is physically easier to be a father than a mother, snails want to father as many snails as possible rather than nurturing great numbers of eggs. Therefore, before mating, pairs maneuver around each other like jousting medieval knights trying to stab each other while avoiding being hit.
The ancient Greeks observed snails and their love darts. Some people speculate that these observations led to the Cupid myth.
Garden snails dig with the foot to bury about 80 mucus-covered eggs in the damp soil when the weather is warm, then cover the “nest” with excrement. After a few weeks of damp, warm conditions, the eggs hatch. A young snail searches immediately for food, eating its eggshell and perhaps any eggs that have not hatched. Mortality rates are high for these snails, and only a few reach adulthood.
When snails hatch, they are miniature adults with a small shell already in place. The shell grows more spirals as the snail grows. As you can see by the photos, most land snails have right-handed shells – if you look at the center, the spirals coil clockwise to the right. To grow its shell, snails need calcium in their diet. If they do not get enough calcium, their shell will be thin or even cracked. A snail adds new material to the outer edge of its shell. The center of the shell is, therefore, the oldest part of the shell. When a snail reaches its final adult size, the shell stops growing, and the snail is ready to reproduce. Adult snails are prolific breeders and may lay eggs every four to six weeks.
Land snails have two sets of retractable tentacles on their head. The upper tentacles contain the eyes, which see mostly shadows. The lower tentacles are used for smelling, tasting and touching, but snails cannot hear. They have microscopic teeth inside the mouth used like a rasp to scrape food into the mouth. Land snails usually eat plants, including leaves, stems, bark, fruit and fungi (I know, not technically a plant). Bacteria and saliva in their crop help break down cellulose into simple sugars.
Snails have many predators, including beetles, snakes, toads, turtles and birds. The shell protects them a bit, but many birds hammer snails against rocks until the soft edible interior is exposed. Other predators, such as frogs, swallow snails whole. To protect against predators, land snails can retract their head and foot into their shell. They tend to stay well hidden in the dirt or leaves when they are not eating. Humans are probably a greater threat to snails than other predators, however. Habitat destruction has caused the extinction of many snail species in recent years, especially in Hawaii.
Because they do not want to dry out, snails are most active at night and on damp, cloudy days. They typically are dormant when the weather is cold, often from about October through April. They may also become dormant in very hot, dry weather. During these times, the snail seals its shell opening with a dry layer of mucus and finds a damp location, such as under a log, to bide its time.
Snails are gastropods, a class of mollusks. Their bodies are essentially the same as those of mussels, abalone, conch and squid, so it’s not such a stretch to eat them. Archaeological evidence shows that humans have eaten snails around the Mediterranean region for at least 12,000 years. In fact, snails may have been the first species raised by humans for food. (And you thought goats were the first farmed animal?) Snails are easy to cultivate and can be raised in large numbers without special equipment. Even today, snails are eaten throughout the world, especially in northern Africa and southern Europe.
The first snails originated 550 million years ago in salty oceans. They breathed through gills. Later, in areas where rivers meet the sea, some snails evolved to live in freshwater rivers. Eventually, these freshwater snails adapted to living on land and developed lungs instead of gills. These snails became our common garden snails and slugs. Some of these land snails with lungs adapted back into ponds and rivers, where they became freshwater snails with lungs.
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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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