Garden Snail
Helix aspersa
Summary 4
Cornu aspersum, known by the common name garden snail, is a species of land snail. As such it is a terrestrial pulmonate gastropod mollusc in the family Helicidae, which include the most commonly familiar land snails. Of all terrestrial molluscs, this species may well be the most widely known. In English texts it was classified under the name Helix aspersa for over two centuries, but the prevailing classification now places it in the genus Cornu.
Description 5
The adult bears a hard, thin calcareous shell 25–40 mm in diameter and 25–35 mm high, with four or five whorls. The shell is variable in color and shade but generally is 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 white and reflected.
The body is soft and slimy, brownish-grey, and the animal retracts itself entirely into the shell when inactive or threatened. When injured or badly irritated the animal produces a defensive froth of mucus that might repel some enemies or overwhelm aggressive small ants or 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 quiescent periods during heat and drought are known as aestivation; its quiescence during winter is known as hibernation. When hibernating, Cornu aspersum avoids the formation of ice in its tissues by altering the osmotic components of its blood (or haemolymph); this permits it to survive temperatures as low as -5°C (23°F). During aestivation, the mantle collar has the ability to change its permeability to water. The snail also has an osmoregulatory mechanism that prevents excessive absorption of water during hibernation. These mechanisms allow Cornu aspersum to avoid either fatal desiccation or hydration during months of either kind of quiescence.
During times of activity the snail's head and "foot" or "belly" 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 chitinousradula with which the snail scrapes and manipulates food particles.
Biology 6
This snail is mainly nocturnal but will emerge after rain during the day. It moves by means of a muscular foot; the mucus secreted by the foot aids with movement and leaves a tell-tale track behind. They feed on a range of plant matter, and can be serious pests of gardens (4). This snail has a strong homing instinct, and spends the day, often in large groups, beneath stones and other structures. They hibernate through the winter in similar locations (5). Garden snails are hermaphrodites, meaning that one individual possesses both male and female reproductive organs; although they are able to self-fertilise, most snails mate with another snail (4). Reproduction takes place in early summer, and begins with pairing and courtship. After a period in which the members of the pair caress each other with their tentacles, each snail pierces the skin of its partner with a calcareous 'love dart', a spiny projection which is covered in mucus. The function of this love dart is unclear, but it is thought that the mucus may act to improve the survival of sperm. Mating then takes place; each snail inserts its penis into its partner at the same time (6). The snails separate, and the sperm is stored internally until the eggs are ripe. After the eggs have been fertilised, the snails dig pits in the soil in which to lay the eggs (5). Hatchlings have translucent, delicate shells (4). The garden snail is edible, and snail farming is currently a booming cottage industry in Britain. This species has also been used for centuries in traditional medicine, for example, broth made from the mucus was used to treat sore throats (7).
Distribution 5
Cornu aspersum is native to the Mediterranean region (including Egypt) and western Europe, from northwest Africa and Iberia, eastwards to Asia Minor, and northwards to the British Isles.
About the beginning of the 20th century, a number of North African endemic forms and subspecies were described on the basis of shell characteristics. The commonest subspecies, Cornu aspersum aspersum (synonym Helix aspersa aspersa), has become very abundant, mainly in agricultural and residential human habitats where the climates is temperate, Mediterranean, or subtropical.
Cornu aspersum is a typically anthropochorous species; it has been spread to many geographical regions by humans, either deliberately or accidentally. Nowadays it is cosmopolitan in temperate zones, and has become naturalised in many regions with climates that differ from the Mediterranean climate in which it evolved. It is present on all continents except Antarctica, and occurs on most major islands as well. Its passive anthropochory is the likeliest explanation for genetic resemblances between allopatric populations. Its anthropochorous spread may have started as early as during the Neolithic revolution some 8500 BP. Such anthropochory continues, sometimes resulting in locally catastrophic destruction of habitat or crops.
Its increasing non-native distribution includes other parts of Europe, such as Bohemia in the Czech Republic since 2008. It is present in Australia, New Zealand, North America and southern South America. It was introduced to Southern Africa as a food animal by Huguenots in the 18th century, and into California as a food animal in the 1850s; it is now a notorious agricultural pest in both regions, especially in citrus groves and vineyards. Many jurisdictions have quarantines for preventing the importation of the snail in plant matter.
Sources and Credits
- (c) Erik Veldhuis; Modified by Tom Meijer, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Helix_aspersa-Nl2A.jpg
- (c) MathKnight 20px, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/MK-snail005.jpg/460px-MK-snail005.jpg
- (c) Ken-ichi Ueda, some rights reserved (CC BY), uploaded by Ken-ichi Ueda
- (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Helix_aspersa
- (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Cornu_aspersum
- Adapted by Ken-ichi Ueda from a work by (c) Wildscreen, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/6693723
More Info
iNat Map
| Establishment | introduced |
|---|---|
| Slug or snail | snail |
