Cornu aspersum
Cornu aspersum | |
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Garden snail (Cornu aspersum) on Limonium | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Gastropoda |
Subclass: | Heterobranchia |
Order: | Stylommatophora |
Family: | Helicidae |
Subfamily: | Helicinae |
Tribe: | Thebini |
Genus: | Cornu |
Species: | C. aspersum
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Binomial name | |
Cornu aspersum (O. F. Müller, 1774)[2]
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Synonyms[3] | |
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Cornu aspersum (syn. Helix aspersa, Cryptomphalus aspersus), known by the
The snail is relished as a food item in some areas, but it is also widely regarded as a pest in gardens and in agriculture, especially in regions where it has been introduced accidentally, and where snails are not usually considered to be a menu item.
Description
The adult bears a hard, thin calcareous shell 25–40 millimetres (1–1+5⁄8 in) in diameter and 25–35 millimetres (1–1+3⁄8 in) high, with four or five whorls. The shell is variable in coloring and shade of color, but generally it has a reticulated pattern of dark brown, brownish-golden, or chestnut with yellow stripes, flecks, or streaks (characteristically interrupted brown colour bands). The aperture is large and characteristically oblique, its margin in adults is whitish and reflected.
The body is soft and slimy, brownish-grey, and able to be retracted entirely into the shell, which the animal does when inactive or threatened. When injured or badly irritated the snail produces a defensive froth of mucus that might repel some enemies or overwhelm aggressive small ants and the like. It has no operculum; during dry or cold weather it seals the aperture of the shell with a thin membrane of dried mucus; the term for such a membrane is epiphragm. The epiphragm helps the snail retain moisture and protects it from small predators such as some ants.
The snail's
During times of activity the snail's head and "foot" emerge. The head bears four tentacles; the upper two are larger and bear eye-like light sensors, and the lower two are tactile and olfactory sense organs. The snail extends the tentacles by internal pressure of body fluids, and retracts all four tentacles into the head by invagination when threatened or otherwise retreating into its shell. The mouth is located beneath the tentacles, and contains a chitinous radula with which the snail scrapes and manipulates food particles.
The shell of Cornu aspersum is almost always right-coiled, but exceptional left-coiled specimens are also known; see Jeremy (snail) for an example.
Taxonomy
The accepted name of the species was long considered to be Helix aspersa, a member of the genus Helix, like the Roman snail Helix pomatia. However, in a number of publications since 1990,[6] it has instead been placed in various genera previously considered as subgenera of Helix. One such genus is Cornu, which is appropriate if the species is considered as congeneric with the species previously known as Helix aperta.[7][8] Then the name would be Cornu aspersum.[9][10][11] Previously there was debate whether Cornu was a valid generic name (because it was first applied to teratological specimens), but a 2015 ruling has confirmed that it is so.[12] Until this was established, Italian research teams and others used the generic name Cantareus instead.[13][14][15][16] Other workers, including Ukrainian and Russian research teams, who regard H. aspersa and H. aperta as being in different genera, call the former Cryptomphalus aspersus.[17][18][19][20]
Analyses based on DNA sequences have now established that C. aspersum and C. aperta share a clade with snails in the genera Otala and Eobania, distinct from the clade containing Helix, so it is no longer tenable to consider them as species of Helix.[21]
Many subspecific varieties have been described on the basis of shell characters (e.g.[22]). The most prominent example nowadays is the subspecies Cornu aspersum maximum (Taylor, 1883),[23] originally described as a large shelled form from Algeria (but perhaps including similar forms from elsewhere). In the recent scientific literature the name has been applied both to large Algerian snails[24] and to a large form found in snail farms.[25] Some Algerian forms are indeed genetically quite distant from the usual, most widespread form, but the large form in snail farms is different again.[26][25] It is also problematic that there was a prior use of the name Helix aspersa maxima unassociated with Algeria.[27] The subspecies maximum is formally considered by some authorities as a junior synonym of Cornu aspersum.[28][29]
Life cycle
Like other Pulmonata, individuals are hermaphrodites, producing both male and female gametes. Reproduction is predominantly, and probably exclusively, by outcrossing.[30][31] During a mating session of several hours, two snails exchange sperm reciprocally. H. aspersa snails stab a calcite spine, known as a love dart, into their partner. The mucus coating the love dart contains a chemical that diverts sperm away from being digested. This is important for sperm competition because individuals mate repeatedly and the donated sperm can remain viable for 4 years.[31][32] About 10 days after fertilisation, the snail lays a batch of on average 50 spherical, pearly-white eggs into crevices in the topsoil, or sheltered under stones.[30] In a year it may lay approximately six batches of eggs.[33] The size of the egg is 3 mm.[30]
After snails hatch from the egg, they mature in one or more years. Maturity takes two years in Southern California, while it takes only 10 months in South Africa.[citation needed] In captivity snails can become sexually mature within 3.5 months of hatching, before they stop growing.[30] The lifespan of snails in the wild is typically 2–3 years.[citation needed]
Distribution
Cornu aspersum is native to the
Cornu aspersum is a typically
Its increasing non-native distribution includes parts of Europe, such as Bohemia in the
A number of North African endemic forms and subspecies have been described on the basis of shell characters. Cornu aspersum aspersum, in French commonly called the "petit gris", is native to the Mediterranean area and Western Europe, but has been spread widely elsewhere. The name Cornu aspersum maximum has been applied to a large form kept in heliciculture (in French commonly called the "gros gris"), but this is genetically distinct from large Algerian forms earlier given this name.[26]
Ecology
Cornu aspersum is a primarily a herbivore. It feeds on numerous types of fruit trees, vegetable crops, rose bushes, garden flowers, and cereals. It also is an omnivorous scavenger that will feed on rotting plant material and on occasion scavenge animal matter, such as crushed snails and worms. Cornu aspersum can obtain the calcium required to build its shell by consuming soil.[43] In turn it is a food source for many other animals, including small mammals, some bird species, lizards, frogs, centipedes, predatory insects such as glowworms in the family Lampyridae, and predatory terrestrial snails.[44] The species may be of use as an indicator of environmental pollution, because it deposits heavy metals, such as lead, in its shell.[45]
Parasites
Parasites of Cornu aspersum include a number of
Behavior
The snail secretes thixotropic adhesive mucus that permits locomotion by rhythmic waves of contraction passing forward within its muscular foot. Starting from the rear, the contraction of the longitudinal muscle fibres above a small area of the film of mucus causes shear that liquefies the mucus, permitting the tip of the tail to move forward. The contracted muscle relaxes while its immediately anteriad transverse band of longitudinal fibres contract in their turn, repeating the process, which continues forward until it reaches the head. At that point the whole animal has moved forward by the length of the contraction of one of the bands of contraction. However, depending on the length of the animal, several bands of contraction can be in progress simultaneously, so that the resultant speed amounts to the speed imparted by a single wave, multiplied by the number of individual waves passing along simultaneously.[50]
A separate type of wave motion that may be visible from the side enables the snail to conserve mucus when moving over a dry surface. It lifts its belly skin clear of the ground in arches, contacting only one to two thirds of the area it passes over. With suitable lighting the lifting may be seen from the side as illustrated, and the percentage of saving of mucus may be estimated from the area of wet mucus trail dabs that it leaves behind. This type of wave passes backwards at the speed of the snail's forward motion, therefore having a zero velocity with respect to the ground.
An estimate from 1974 for a top speed of 0.03 mph (1.3 cm/s)[51] has become popular.[52][53] However, this estimate has been questioned since in competitions between snails only speeds of 2.4 mm/s have been achieved.[54]
Cornu aspersum has a strong homing instinct, readily returning to a regular hibernation site.[55]
Human relevance
The species is known as an agricultural and garden pest, an edible delicacy, and occasionally a household
Approaches to snail pest control
There are a variety of snail-control measures that gardeners and farmers use in an attempt to reduce damage to valuable plants. Traditional pesticides are still used, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is also a snail repellent, and thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. Caffeine has proven surprisingly toxic to snails, to the extent that spent coffee grounds (not decaffeinated) make a safe and immediately effective snail-repellant and even molluscicidal mulch for pot-plants, or for wherever else the supply is adequate.[citation needed]
The decollate snail (Rumina decollata) will capture and eat garden snails, and because of this it has sometimes been introduced as a biological pest control agent.[57] However, this is not without problems, as the decollate snail is just as likely to attack and devour other species of gastropods that may represent a valuable part of the native fauna of the region.
Pharmacological studies
Cornu aspersum has gained some popularity as the chief ingredient in skin creams and gels (crema/gel de caracol) sold in the US. These creams are promoted as being suitable for use on wrinkles, scars, dry skin, and acne to reduce pigmentation, scarring, and wrinkles.[58]
Secretions of Cornu aspersum produced under stress have skin-regenerative properties because of antioxidant superoxide dismutase and glutathione S-transferase (GSTs) activities. The secretions can stimulate fibroblast proliferation and rearrange the actin cytoskeleton stimulate extracellular matrix assembly and regulation of metalloproteinase activities for regeneration of wounded tissue.[59]
The mucus of Cornu aspersum contains a rich source of substances that can be used to treat biotic human diseases. Nine fractions of compounds with varying molecular weight were purified from the mucus and was tested against gram-positive and gram-negative bacterial strains. Results found three fractions exhibited predominant antibacterial activity against the gram-positive strain.[60]
While further confirmatory research is still needed, potential benefits of the snail extracts or secretion filtrates have been also demonstrated in other disease models in mice, including protective effects against ethanol-induced gastric ulcer[61] and against the progression of Alzheimer's type dementia.[62]
References
This article incorporates CC-BY-2.0 text from reference.[38]
- IUCN Red List of Threatened Species. 2011: e.T156890A5012868.
- ^ Müller O. F. (1774). Vermivm terrestrium et fluviatilium, seu animalium infusoriorum, helminthicorum, et testaceorum, non marinorum, succincta historia. Volumen alterum. pp. I-XXVI [= 1-36], 1-214, [1-10]. Havniae & Lipsiae. (Heineck & Faber).
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Further reading
External links
Media related to Helix aspersa at Wikimedia Commons
- Helix aspersa at Animalbasetaxonomy, short description, distribution, biology, status (threats), images
- Helix aspersa images at Encyclopedia of Life including genitalia drawings
- brown garden snail on the UF / IFAS Featured Creatures website
- Canada Agriculture Fact Sheet
- BBC Info Page
- Extreme Close-Up Video of the North American Garden Snail
- University of California Pest Management Guidelines: Brown Garden Snail
- Video of froth protection response of Cornu aspersum
- Zachi Evenor, A video showing a garden snail (Cornu aspersum / Helix aspersa) in action, YouTube, November 9, 2013