Snails are any number of shelled mollusks falling under the subphylum Gastropoda. Snails have a wide range of diets ranging from the herbivorous to the carnivorous. Land snails subsist on a diet of mainly algae, fruit, bark, fungi, and decaying plant matter.
A handful of land snail species are carnivorous, such as the Powelliphanta, a genus of snails native to New Zealand that feed on earthworms. Sea snails, likewise, live on a diet of algae and other water-located plants, as well as small water-dwelling invertebrates.
Snails are found all over the world in a variety of biomes’ deserts, savannahs, forests, lakes, oceans, grasslands, etc. Humans may be most familiar with land-dwelling species of snail, but the majority of snails are actually water-dwelling species.
Snails hold a lot of cultural significance as food, pests, and vectors for disease. Snails, due to their slow movement, are often used as a symbol to represent laziness or sloth. The term “snail” has come to reference any process that occurs slowly, as used in the phrases “at a snail’s pace” or “snail mail.”
Like all mollusks, snails are invertebrates that lack an internal skeleton. The bottom on the snail, the part used for motion, is called the foot. Snails move by the rhythmic contraction of muscles in the foot. All over their bodies, the excrete a slimy mucus that helps them overcome friction to move and which keeps the snail’s moist body from drying out. This is one of the reasons why salt is deadly to snails; the salt absorbs their moisture and dries them out. Snails move very slowly; about a rate of 1mm per second. The mucus secreted by a snail leaves a characteristic shiny slime trail.
Snails vary greatly in size. The largest known species of snail is the Giant African Snail which can reach lengths up to 30 cm (1 foot). The smallest known snail is the Chinese Angustopila dominikae, which averages about 0..08 cm (0.03 inches). Most snails have one to 2 pairs of tentacles located on their head. One pair contains the eyestalks and the other pair is used as an olfactory organ.
The most obvious features of snails are their characteristic shells. Shells originally develop in the larval stage and stay with the snail the rest of its life, growing in tandem with its body. Most snail shells are composed out of the compound calcium carbonate. The snail will secrete calcium carbonate through its skin, which sticks to the shell and causes it to grow larger. As such, snails require a steady source of calcium to keep their shell strong. Snails raised in acidic environments or environments with low calcium levels have weak, brittle shells. Typically, snails are able to retract into their shells as a form of self-defense. Snail shells tend to grow in the shape of a logarithmic spiral that has a right-handed chirality.
Snails have a relatively complex internal anatomy, complete with specialized organs and tissues. Snails have a small brain composed of a cluster of cerebral ganglia. Though smaller than the brains of mammals, most snail brains are still complex enough to allow for associative learning. Some species of snails use lungs for respiration while others use gills. Interestingly, there is a sizable number of land-dwelling snails that have gills and water-dwelling snails that have lungs.
Snails eat their food using the radula, a tongue-like chitinous structure lined with teeth used to rip food apart. After sufficient breakup, the food travels to the gastrointestinal tract to be digested. In quiet places, one can actually hear the snail “chew” its food as the radula breaks it up.
Most species of snail are hermaphrodites, meaning that they possess both sets of sex organs.
The average lifespan of a snail varies greatly from species to species. Some snails have a lifespan of only 6 weeks while some can live up to 5 years in favorable conditions. One species, the Roman snail Helix pomatia routinely lives up to 10 years in the wild and an estimated 25 years in captivity.
Unlike insects and arthropods, most snails do not go through distinct developmental phases, though they have stages of immaturity and maturity that are commonly called ‘larval’ and ‘adult’ stages respectively. A handful of sea snails do have an anatomically distinct larval stage called a trochophore stage. Snails are capable of halting their development, as many species go into a hibernation-like state during the winter. Some snails also halt development during the arid and dry months of the summer, a behavior called estivation.
When snail eggs, hatch, the larvae typically have a small or in some cases transparent shell. As soon as the hatch, snail larvae scour the area looking for calcium-containing food. The calcium they get from food helps them build their shell and grow into a mature adult specimen. As stated previously, most snails are herbivorous and eat plants, wood, fungi, fruit, and vegetables. Some opt to eat small invertebrates like earthworms and insect larvae.
Once the snail larva is fully mature, it will begin looking for opportunities to mate. Snails engage in courtship rituals, typically in the form of chemical signaling and touch. Prior to mating, each snail will attempt to inject the other with a ‘love dart,’ a sharp exterior appendage made from calcium. This love dart does not contain the sperm that is transferred between mating pairs. Instead, it is thought that the love dart contains hormones that make the injected individual more receptive to mating and increase the chance of survival of sperm. Incidentally, it is thought that the idea of Cupid’s love arrow may stem from the love dart behavior of snails.
After injecting one or the other with a love dart, the two snails will copulate, exchanging sperm and ova. Once the eggs are fertilized, both snails will seek a suitable place to lay their eggs. Snails typically lay their eggs in damp areas with a lot of soil so that hatched larva have an immediate source of food. An individual snail typically lays about 100 eggs per brood and can lay eggs at least once a month. A handful of snail species are capable of pathonogenesis—that is reproduction without fertilization.
Snails & Humans
Snails and humans have had a long relationship. Because they are primarily herbivorous, some species of snails are known as agricultural pests that can eat and damage crops. In other parts of the world snails are a common food item, even considered a delicacy in some places.
The French, for example, are known for their traditional dish snails called Escargot (the word for snail in French is just les escargots). Cooked snails are known for their salty and slightly rubbery texture, and are often compared to shrimp in terms of taste. Other countries that routinely eat snails are the Philippines, Morocco, China, Indonesia, Ghana, Nigeria, and Spain. In fact, snails seem to be a relatively common food item in most parts of the world, barring Western non-European countries. Snail eggs are also served similar to caviar. The practice of raising snails for human consumption is called heliciculture. Snails are also sometimes raised for cosmetic purposes, as the mucus produced by snails is used to make facial products or wrinkles, scars, and acne.
Snails are also extremely popular in art, symbolism, and cultural metaphors. Snails, due to their slow movement, are often associated with the vice of sloth in Christian symbolism, and the image of the snail has become a universal reference for something that is slow or takes a long time to occur; for example, in the phrases “at a snail’s pace” or “snail mail.” For the Aztecs, the snail symbolized rebirth and was associated with the moon, and snails were used in divination practices of the Greeks. The popular Indonesian folktale Keong Emas recounts the story of a princess who was transformed into a golden snail and saved by her lover.
In a particularly interesting example of snail symbolism, artwork and manuscripts from 13th and 14th-century medieval Europe are littered with images of armored knights fighting large snails. To date, there is not much agreement among scholars of history as to the meaning of these images, but it is thought that the references to snails might represent socially undesirable groups such as the Lombards, a Germanic tribe considered by many medieval Europeans to be dangerous outsiders. Alternatively, the presence of snails could just be a huge running joke among medieval artists; the 14th-century version of an internet meme.
In addition, snail races are actually a real thing. Many countries, the U.K., in particular, have a niche culture of snail racing. In fact, every year there is a World Championship Snail Race, the most recent one taking place in this past July in Norfolk, England. Various snail enthusiasts from the around the world conglomerate to show off their prized snails and compete in races around a circular track, almost as if they were racing horses. The most recent world champion is a snail named Hosta, who beat out the competition of 10 other snails to be crowned fastest snail in the world.