Land snail

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Helix pomatia, a species of air-breathing land snail used for escargot, is a little bit larger than the common garden snail. Grapevinesnail 01.jpg
Helix pomatia , a species of air-breathing land snail used for escargot, is a little bit larger than the common garden snail.
Cornu aspersum (previously Helix aspersa) - the common garden snail - in Israel Snail-wiki-120-Zachi-Evenor.jpg
Cornu aspersum (previously Helix aspersa) – the common garden snail – in Israel
Colonies of snails in Sicily Animals-Sicily-bjs-3.jpg
Colonies of snails in Sicily

A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. Land snail is the common name for terrestrial gastropod mollusks that have shells (those without shells are known as slugs). However, it is not always easy to say which species are terrestrial, because some are more or less amphibious between land and fresh water, and others are relatively amphibious between land and salt water.

Contents

Land snails are a polyphyletic group comprising at least ten independent evolutionary transitions to terrestrial life (the last common ancestor of all gastropods was marine). [1] [2] [3] [4] [5] The majority of land snails are pulmonates that have a lung and breathe air. Most of the non-pulmonate land snails belong to lineages in the Caenogastropoda, and tend to have a gill and an operculum. The largest clade of land snails is the Cyclophoroidea, with more than 7,000 species. [6] Many of these operculate land snails live in habitats or microhabitats that are sometimes (or often) damp or wet, such as in moss.

Land snails have a strong muscular foot; they use mucus to enable them to crawl over rough surfaces and to keep their soft bodies from drying out. Like other mollusks, land snails have a mantle, and they have one or two pairs of tentacles on their head. Their internal anatomy includes a radula and a primitive brain. In terms of reproduction, many caenogastropod land snails (e.g., diplommatinids) are dioecious, [7] [8] but pulmonate land snails are hermaphrodites (they have a full set of organs of both sexes) and most lay clutches of eggs in the soil. Tiny snails hatch out of the egg with a small shell in place, and the shell grows spirally as the soft parts gradually increase in size. Most land snails have shells that are right-handed in their coiling.

A wide range of different vertebrate and invertebrate animals prey on land snails. They are used as food by humans in various cultures worldwide, and are raised on farms in some areas for use as food.

Biology

Physical characteristics

"The Teeth of a Snail" from Robert Hooke's Micrographia, 1665. This actually shows the jaw, against which the teeth on the radula act. Micrographia Schem 25 fig 1.jpg
"The Teeth of a Snail" from Robert Hooke's Micrographia, 1665. This actually shows the jaw, against which the teeth on the radula act.
Sphincterochila boissieri in Hamakhtesh Hagadol, northern Negev. Diameter is 2.1 cm. Sphincterochila boissieri Negev.jpg
Sphincterochila boissieri in Hamakhtesh Hagadol, northern Negev. Diameter is 2.1 cm.
Underside of a snail climbing a blade of grass, showing the muscular foot and the pneumostome or respiratory pore on the animal's right side Snail climbing grass SMC 07.jpg
Underside of a snail climbing a blade of grass, showing the muscular foot and the pneumostome or respiratory pore on the animal's right side

Land snails move by gliding along on their muscular foot, which is lubricated with mucus and covered with epithelial cilia. [9] This motion is powered by succeeding waves of muscular contractions that move down the ventral of the foot. This muscular action is clearly visible when a snail is crawling on the glass of a window or aquarium. [10] Snails move at a proverbially low speed (1 mm/s is a typical speed for adult Helix lucorum [11] ). Snails secrete mucus externally to keep their soft bodies from drying out. They also secrete mucus from the foot to aid in locomotion by reducing friction, and to help reduce the risk of mechanical injury from sharp objects, meaning they can crawl over a sharp edge like a straight razor and not be injured. [12] The mucus that land snails secrete with the foot leaves a slime trail behind them, which is often visible for some hours afterwards as a shiny "path" on the surface over which they have crawled.

Snails (like all molluscs) also have a mantle, a specialized layer of tissue which covers all of the internal organs as they are grouped together in the visceral mass. The mantle also extends outward in flaps which reach to the edge of the shell and in some cases can cover the shell, and which are partially retractable. The mantle is attached to the shell, and creates the shell and makes shell growth possible by secretion.

Most molluscs, including land snails, have a shell which is part of their anatomy since the larval stage. When they are active, the organs such as the lung, heart, kidney, and intestines remain inside the shell; only the head and foot emerge. The shell grows with them in size by the process of secreting calcium carbonate along the open edge and on the inner side for extra strength. Although some land snails create shells that are almost entirely formed from the protein conchiolin, most land snails need a good supply of calcium in their diet and environment to produce a strong shell. A lack of calcium, or low pH in their surroundings, can result in thin, cracked, or perforated shells. Usually a snail can repair damage to its shell over time if its living conditions improve, but severe damage can be fatal. When retracted into their shells, many snails with gills (including some terrestrial species) are able to protect themselves with a door-like anatomical structure called an operculum .

Land snails range greatly in size. The largest living species is the Giant African Snail or Ghana Tiger Snail ( Achatina achatina ; Family Achatinidae), which can measure up to 30 cm. [13] [14] The largest land snails of non-tropical Eurasia are endemic Caucasian snails Helix buchi and Helix goderdziana from the south-eastern Black Sea area in Georgia and Turkey; diameter of the shell of the latter may exceed 6 cm. [15]

Most land snails bear one or two pairs of tentacles on their heads. In most land snails the eyes are carried on the first (upper) set of tentacles (called ommatophores or more informally 'eye stalks') which are usually roughly 75% of the width of the eyes. The second (lower) set of tentacles act as olfactory organs. Both sets of tentacles are retractable in land snails.

Digestion and nervous system

Light micrograph of a section through a snail's eye (Helix pomatia). 1 anterior chamber, 2 lens in the posterior chamber, 3 retina, 4 optic nerve Snail 02.jpg
Light micrograph of a section through a snail's eye (Helix pomatia). 1 anterior chamber, 2 lens in the posterior chamber, 3 retina, 4 optic nerve
The anatomy of a common snail Snail diagram-en edit1.svg
The anatomy of a common snail
Garden snail (Cornu aspersum) defecating Garden snail defecating.jpg
Garden snail (Cornu aspersum) defecating

A snail breaks up its food using the radula inside its mouth. The radula is a chitinous ribbon-like structure containing rows of microscopic teeth. With this the snail scrapes at food, which is then transferred to the digestive tract. In a very quiet setting, a large land snail can be heard 'crunching' its food: the radula is tearing away at the surface of the food that the snail is eating.

The cerebral ganglia of the snail form a primitive brain which is divided into four sections. This structure is very much simpler than the brains of mammals, reptiles and birds, but nonetheless, snails are capable of associative learning. [16]

Respiration

Burgundy snail (H. pomatia) Snail.jpg
Burgundy snail (H. pomatia)

Since snails in the genus Helix are terrestrial rather than freshwater or marine, they have developed a simple lung for respiration. (Most other snails and gastropods have gills, instead.)

Oxygen is carried by the blood pigment hemocyanin. Both oxygen and carbon dioxide diffuse in and out of blood through the capillaries. A muscular valve regulates the process of opening and closing the entrance of the lung. When the valve opens, the air can either enter or leave the lung. The valve plays an important role in reducing water loss and preventing drowning.

Shell growth

As the snail grows, so does its calcium carbonate shell. The shell grows additively, by the addition of new calcium carbonate, which is secreted by glands located in the snail's mantle. The new material is added to the edge of the shell aperture (the opening of the shell). Therefore, the centre of the shell's spiral was made when the snail was younger, and the outer part when the snail was older. When the snail reaches full adult size, it may build a thickened lip around the shell aperture. At this point the snail stops growing, and begins reproducing.

A snail's shell forms a logarithmic spiral. Most snail shells are right-handed or dextral in coiling, meaning that if the shell is held with the apex (the tip, or the juvenile whorls) pointing towards the observer, the spiral proceeds in a clockwise direction from the apex to the opening.

Hibernation and estivation

Some snails hibernate during the winter (typically October through April in the Northern Hemisphere). They may also estivate in the summer in drought conditions. To stay moist during hibernation, a snail seals its shell opening with a dry layer of mucus called an epiphragm .

Reproduction

The use of love darts by the land snail Monachoides vicinus is a form of sexual selection Monachoides vicinus dart lateral.jpg
The use of love darts by the land snail Monachoides vicinus is a form of sexual selection
Snails mating in Los Angeles Snails mating in Los Angeles.jpg
Snails mating in Los Angeles
Two Helicid snails make contact prior to mating. Kissingsnails.jpg
Two Helicid snails make contact prior to mating.
Two Helix pomatia snails mating Helix pomatia copulation 2012 G1.jpg
Two Helix pomatia snails mating

The great majority of land snails are hermaphrodites with a full set of reproductive organs of both sexes, able to produce both spermatozoa and ova. A few groups of land snails such as the Pomatiidae, which are distantly related to periwinkles, have separate sexes: male and female. The age of sexual maturity varies depending on species of snail, ranging from as little as 6 weeks [17] to 5 years. [18] Adverse environmental conditions may delay sexual maturity in some snail species. [19]

Most pulmonate air-breathing land snails perform courtship behaviors before mating. The courtship may last anywhere between two and twelve hours. In a number of different families of land snails and slugs, prior to mating one or more love darts are fired into the body of the partner.

Pulmonate land snails are prolific breeders and inseminate each other in pairs to internally fertilize their ova via a reproductive opening on one side of the body, near the front, through which the outer reproductive organs are extruded so that sperm can be exchanged. Fertilization then occurs and the eggs develop. Each brood may consist of up to 100 eggs.

Garden snails bury their eggs in shallow topsoil primarily while the weather is warm and damp, usually 5 to 10 cm down, digging with their foot. Egg sizes differ between species, from a 3 mm diameter in the grove snail to a 6 mm diameter in the Giant African Land Snail. After 2 to 4 weeks of favorable weather, these eggs hatch and the young emerge. Snails may lay eggs as often as once a month.

There have been hybridizations of snail species; although these do not occur commonly in the wild, in captivity they can be coaxed into doing so.

Parthenogenesis has been reported only in one species of slug, [20] but many species can self-fertilise. [21]

C. obtusus is a prominent endemic snail species of the Eastern Alps. There is strong evidence for selfing (self-fertilization) in the easternmost snail populations as indicated by microsatellite data. [22] Compared to western populations, in the eastern population mucous gland structures employed in sexual reproduction are highly variable and deformed suggesting that in selfing organisms these structures have reduced function. [22]

Lifespan

Most species of land snail are annual, others are known to live 2 or 3 years, [23] [24] but some of the larger species may live over 10 years in the wild. [25] For instance, 10-year old individuals of the Roman snail Helix pomatia are probably not uncommon in natural populations. [26] Populations of some threatened species may be dependent on a pool of such long-lived adults. [27] In captivity, the lifespan of snails can be much longer than in the wild, for instance up to 25 years in H. pomatia. [28]

Diet

In the wild, snails eat a variety of different foods. Terrestrial snails are usually herbivorous, however some species are predatory carnivores or omnivores, including the genus Powelliphanta , which includes the largest carnivorous snails in the world, native to New Zealand. [29] The diet of most land snails can include leaves, stems, soft bark, fruit, vegetables, fungi and algae. They may have a specialized crop of symbiotic bacteria that aid in digestion, especially with the breakdown of the polysaccharide cellulose into simple sugars. Some species can cause damage to agricultural crops and garden plants, and are therefore often regarded as pests.

Predators

Many predators, both specialist and generalist, feed on snails. Some animals, such as the song thrush, break the shell of the snail by hammering it against a hard object, such as stone, to expose its edible insides. Other predators, such as some species of frogs, circumvent the need to break snail shells by simply swallowing the snail whole, shell and all.

Some carnivorous species of snails, such as the decollate snail and the rosy wolf snail, also prey on other land snails. Such carnivorous snails are commercially grown and sold to combat pest snail species. Many of these also escape into the wild, where they prey on indigenous snails, such as the Cuban land snails of the genus Polymita , and the indigenous snails of Hawaii.

The larva of a glowworm (Lampyris noctiluca) attacking and eating a land snail Raupe schnecke.JPG
The larva of a glowworm ( Lampyris noctiluca ) attacking and eating a land snail

In an attempt to protect themselves against predators, land snails retract their soft parts into their shell when they are resting; some bury themselves. Land snails have many natural predators, including members of all the land vertebrate groups, three examples being thrushes, hedgehogs and Pareas snakes. Invertebrate predators include decollate snails, ground beetles, leeches, certain land flatworms such as Platydemus manokwari [30] and even the predatory caterpillar Hyposmocoma molluscivora .

In the case of the marsh snail Succinea putris , the snails can be parasitized by a microscopic flatworm of the species Leucochloridium paradoxum , which then reproduces within the snail's body. The flatworms invade the snail's eye stalks, causing them to become enlarged. Birds are attracted to and consume these eye stalks, consuming the flatworms in the process and becoming the final hosts of the flatworm. [31]

Human activity poses great dangers to snails in the wild. Pollution and habitat destruction have caused the extinction of a considerable number of snail species in recent years. [32] [33]

Ecology

Snails easily suffer moisture loss. Snails are most active at night and after rainfall. During unfavourable conditions, a snail remains inside its shell, usually under rocks or other hiding places, to avoid being discovered by predators. In dry climates, snails naturally congregate near water sources, including artificial sources such as wastewater outlets of air conditioners.

Human food

A snail farm in Provence Eyragues-l-Escargot-des-Alpilles-5738.jpg
A snail farm in Provence

Land snails have been eaten for thousands of years, going back at least as far as the Pleistocene. Archaeological evidence of snail consumption is especially abundant in Capsian sites in North Africa, but is also found throughout the Mediterranean region in archaeological sites dating between 12,000 and 6,000 years ago. [34] [35] Snail eggs, sold as snail caviar, are a specialty food that is growing in popularity in European cuisine. [36] Snails contain many nutrients. They are rich in calcium and also contain vitamin B1 and E. They contain various essential amino acids, and are low in calories and fat.[ citation needed ] However, wild-caught land snails which are prepared for the table but are not thoroughly cooked, can harbor a parasite ( Angiostrongylus cantonensis ) that can cause a rare kind of meningitis. [37] The process of snail farming is called heliciculture. The establishment of snail farms outside of Europe has introduced several species to North America, South America, and Africa, where some escapees have established themselves as invasive species. [38] [39] [40] [41]

Africa

In parts of West Africa, specifically Ghana, snails are served as a delicacy. [42] Achatina achatina , Ghana tiger snails, are also known as some of the largest snails in the world. Snail, called "igbin" in Yoruba language is a delicacy, widely eaten in Nigeria, especially among the Yorubas and Igbos. In Cameroon, snails, usually called 'nyamangoro' and 'slow boys' are a delicacy especially to natives of the South West region of Cameroon. The snails are either eaten cooked and spiced or with a favourite dish called 'eru'.

In North Morocco, small snails are eaten as snacks in spicy soup. The recipe is identical to this prepared in Andalusia (South Spain), showing the close cultural relationship between both kinds of cuisine.

Europe

Snails are eaten in several European countries, as they were in the past in the Roman Empire. Mainly three species, all from the family Helicidae, are ordinarily eaten:

Snails are a delicacy in French cuisine, where they are called escargots . 191 farms produced escargots in France as of 2014. [43] In an English-language menu, escargot is generally reserved[ citation needed ] for snails prepared with traditional French recipes (served in the shell with a garlic and parsley butter). Before preparing snails to eat, the snails should be fasting for three days with only water available. After three days of fasting, the snails should be fed flour and offered water for at least a week. This process is thought to cleanse the snails.

Portuguese caracois snack, species Theba pisana. Portuguese snails' snack.JPG
Portuguese caracóis snack, species Theba pisana .

Snails are also popular in Portuguese cuisine where they are called in Portuguese caracóis, and served in cheap snack houses and taverns, usually stewed (with different mixtures of white wine, garlic, piri piri, oregano, coriander or parsley, and sometimes chouriço). Bigger varieties, called caracoletas (especially, Cornu aspersum), are generally grilled and served with a butter sauce, but other dishes also exist such as feijoada de caracóis. Overall, Portugal consumes about 4,000 tonnes of snails each year. [44]

Cooked French escargots, species Helix pomatia Cooked snails.JPG
Cooked French escargots, species Helix pomatia
Cooked Spanish "caracoles a la madrilena", species Cornu aspersum Caracoles-Cascorro.jpg
Cooked Spanish "caracoles a la madrileña", species Cornu aspersum

Traditional Spanish cuisine also uses snails ("caracoles" in Spanish; "caragols" or "cargols" in Catalan), consuming several species such as Cornu aspersum, Otala lactea , Otala punctata and Theba pisana . Snails are very popular in Andalusia, Valencia and Catalonia. There are even snail celebrations, such as the "L'Aplec del Caragol", which takes place in Lleida each May and draws more than 200,000 visitors from abroad.

Small to medium-sized varieties are usually cooked in one of several spicy sauces or even in soups, and eaten as an appetizer. The bigger ones may be reserved for more elaborate dishes, such as the "arroz con conejo y caracoles" (a paella-style rice with snails and rabbit meat, from the inner regions of south-eastern Spain), "cabrillas" (snails in spicy tomato sauce, typical of western Andalusia) and the Catalan caragols a la llauna (grilled inside their own shells and then eaten after dipping them in garlic mayonnaise) and a la gormanda (boiled in tomato and onion sauce).

In Greece, snails are especially popular in the island of Crete, but are also eaten in many parts of the country and can even be found in supermarkets, sometimes placed alive near partly refrigerated vegetables. In this regard, snails are one of the few live organisms sold at supermarkets as food. They are eaten either boiled with vinegar added, or sometimes cooked alive in a casserole with tomato, potatoes and squashes. Limpets and sea snails also find their way to the Greek table around the country. Another snail cooking method is the Kohli Bourbouristi (κοχλιοί μπου(ρ)μπουριστοί), [45] a traditional Cretan dish, which consists of fried snails in olive oil with salt, vinegar and rosemary.

They often feature on Cyprus taverna menus, in the meze section, [46] under the name karaoloi (καράολοι). [47]

In Sicily, snails (or babbaluci as they are commonly called in Sicilian) are a very popular dish. They are usually boiled with salt first, then served with tomato sauce or bare with oil, garlic and parsley. Snails are similarly appreciated in other Italian regions, such as Piedmont where in Cherasco there is the Italian National Institute of Heliculture.

Snails (or bebbux as they are called in Maltese) are a dish on the Mediterranean island of Malta, generally prepared and served in the Sicilian manner.

In southwestern Germany there is a regional specialty of soup with snails and herbs, called "Black Forest Snail Chowder" (Badener Schneckensuepple).

Heliciculture is the farming of snails. Some species such as the Roman snail are protected in the wild in several European countries and must not be collected, but the Roman Snail and the Garden Snail (Cornu aspersum) are cultivated on snail farms. [28]

Although there is not usually considered to be a tradition of snail eating in Great Britain, common garden snails Cornu aspersum were eaten in the Southwick area of Sunderland in North East England. They were collected from quarries and along the stone walls of railway embankments during the winter when the snails were hibernating and had voided the contents of their guts. Gibson writes that this tradition was introduced in the 19th century by French immigrant glass workers. [48] "Snail suppers" were a feature of local pubs and Southwick working men were collecting and eating snails as late as the 1970s, though the tradition may now have died out.

Oceania

Bulime cooked in garlic butter in Ile des Pins, New Caledonia, species Placostylus fibratus Ile des Pins snails cooked.jpg
Bulime cooked in garlic butter in Ile des Pins, New Caledonia, species Placostylus fibratus

In New Caledonia, Placostylus fibratus (French: bulime) is considered a highly prized delicacy and is locally farmed to ensure supplies. [49] It is often served by restaurants prepared in the French style with garlic butter.

Prevention

Metaldehyde and iron phosphate can be used to exterminate snails. [50] Since copper generates electric shocks that make it difficult for snails to move, it makes a great barrier material for them. [51]

See also

Related Research Articles

<span class="mw-page-title-main">Snail</span> Shelled gastropod

A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also used for most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into. When the word "snail" is used in this most general sense, it includes not just land snails but also numerous species of sea snails and freshwater snails. Gastropods that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell are often called semi-slugs.

<i>Helix</i> (gastropod) Genus of gastropods

Helix is a genus of large, air-breathing land snails native to the western Palaearctic and characterized by a globular shell.

<i>Cornu aspersum</i> Species of edible land snail

Cornu aspersum, known by the common name garden snail, is a species of land snail in the family Helicidae, which includes some of the most familiar land snails. Of all terrestrial molluscs, this species may well be the most widely known. It was classified under the name Helix aspersa for over two centuries, but the prevailing classification now places it in the genus Cornu.

<i>Helix pomatia</i> Species of gastropod

Helix pomatia, common names are the Roman snail, Burgundy snail, or escargot, is a species of large, air-breathing stylommatophoran land snail native to Europe. It is characterized by a globular brown shell. It is an edible species. Helix pomatia commonly occurs synanthropically throughout its range.

<i>Brachylaima</i> Genus of flukes

Brachylaima is a genus of trematodes that can infect the gastrointestinal tract of human beings.

<span class="mw-page-title-main">Heliciculture</span> Snail farming

Heliciculture, commonly known as snail farming, is the process of raising edible land snails, primarily for human consumption or cosmetic use. The meat and snail eggs a.k.a. white caviar can be consumed as escargot and as a type of caviar, respectively.

<span class="mw-page-title-main">Epiphragm</span>

An epiphragm is a temporary structure which can be created by many species of shelled, air-breathing land snails, terrestrial pulmonate gastropod mollusks. It can also be created by freshwater snails when temporary pools dry up.

<span class="mw-page-title-main">Helicidae</span> Family of gastropods

Helicidae is a large, diverse family of western Palaearctic, medium to large-sized, air-breathing land snails, sometimes called the "typical snails." It includes some of the largest European land snails, several species are common in anthropogenic habitats, and some became invasive on other continents. A number of species in this family are valued as food items, including Cornu aspersum the brown or garden snail, and Helix pomatia. The biologies of these two species in particular have been thoroughly studied and documented.

<i>Helix lucorum</i> Species of gastropod

Helix lucorum is a species of large, edible, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Helicidae, the typical snails.

<span class="mw-page-title-main">Slug</span> Shell-less terrestrial gastropod mollusc

Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word slug is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a small internal shell, particularly sea slugs and semi-slugs.

<i>Riccardoella limacum</i> Species of mite

Riccardoella limacum or the white snail mite is a member of the Acari (mite) family which is parasitic primarily on snails. Slug mites are very small, white, and can be seen to move very rapidly over the surface of their host, particularly under the shell rim and near the pulmonary aperture. While once thought to be benign mucophages, more recent studies have shown that they actually subsist on the host's blood, and may bore into the host's body to feed.

<span class="mw-page-title-main">Love dart</span> Darts that some snails shoot into each other during mating

A love dart is a sharp, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts are both formed and stored internally in a dart sac. These darts are made in sexually mature animals only, and are used as part of the sequence of events during courtship, before actual mating takes place. Darts are quite large compared to the size of the animal: in the case of the semi-slug genus Parmarion, the length of a dart can be up to one fifth that of the semi-slug's foot.

<i>Eobania vermiculata</i> Species of gastropod

Eobania vermiculata also known as Helix vermiculata, common name the "chocolate-band snail" is a species of large, air-breathing, land snail, a terrestrial pulmonate gastropod mollusk in the family Helicidae, the true snails or typical snails.

<span class="mw-page-title-main">Reproductive system of gastropods</span>

The reproductive system of gastropods varies greatly from one group to another within this very large and diverse taxonomic class of animals. Their reproductive strategies also vary greatly, see mating of gastropods.

<i>Rathouisia leonina</i> Species of gastropod

Rathouisia leonina is a species of carnivorous air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Rathouisiidae. This species is endemic to China.

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