Helix aspersa

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Helix aspersa

Helix aspersa
Conservation status
NE[1]
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Family: Helicidae
Genus: Helix
Species: H. aspersa
Binomial name
Helix aspersa
(O. F. Müller, 1774)[2]

Helix aspersa, known by the common name garden snail, is a pulmonate gastropod that is one of the best-known of all terrestrial molluscs. It has two recent synonyms: Cornu aspersum and Cantareus aspersus.[3]

Although this species is edible, it is often regarded as a pest in gardens, especially where it has been accidentally introduced.

Contents

[edit] Distribution

It is native to the Mediterranean region (including Egypt[4]) and western Europe, from northwest Africa and Iberia east to Asia Minor, and north to the British Isles. However, it is very widely introduced and naturalised elsewhere in the world.[5][6]

[edit] Description

Helix aspersa

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 somewhat variable in colour and shade but is generally dark brown or chestnut with yellow stripes, flecks, or streaks.

The body is soft and slimy, brownish-grey, and is retracted entirely into the shell when the animal is inactive or threatened. During dry and cold weather, the aperture of the shell is sealed with a thin membrane of dried mucus which is known as an epiphragm, which helps the snail retain moisture. The resultant quiescent periods are known as aestivation and hibernation respectively. When hibernating, Helix aspersa avoids ice formation by altering the osmotic components of its blood (or haemolymph), and can survive temperatures as low as -5°C.[7] During aestivation, the mantle collar has the unique ability to change its permeability to water.[8] In combination with an osmoregulatory mechanism similar to that seen during hibernation this allows Helix aspersa to survive several months of aestivation.

During times of activity the head and foot emerge. The head bears four tentacles, the upper two of which have eye-like light sensors, and the lower two of which are smaller, tactile and olfactory sensory structures. The tentacles can be retracted into the head. The mouth is located beneath the tentacles, and contains a chitinous radula which the snail uses to scrape and manipulate food particles.

Snails are Gastropoda, belonging to the phylum Mollusca. This phylum also includes: bivalvia, the family of oysters, mussels and clams; and cephalopoda: squid and octopi.

[edit] Behaviour

Helix aspersa feeding in captivity

The snail's muscular foot contracts to move the animal, and secretes mucus to facilitate locomotion by reducing friction against the substrate.[6] It moves at a top speed of 1.3 centimetres per second (47 meters per hour),[9] and has a strong homing instinct, readily returning to a regular hibernation site.[10]

[edit] Ecology

Helix aspersa

The garden snail is herbivorous and has a wide range of host plants. It damages numerous types of fruit trees, vegetable crops, garden flowers, and cereals.

It is a food source for many other animals, including small mammals, many bird species, lizards, frogs, centipedes, predatory insects, and predatory terrestrial snails.

There is a variety of snail control measures that gardeners and farmers can take to reduce damage. Traditional pesticides are still in use, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is repellent to snails. A copper band around the trunk of a tree will prevent snails from reaching the foliage and fruit.

Helix aspersa can be used as an indicator of environmental contamination, as its shell acts as a site for deposition of toxic heavy metals, such as lead.[11]

The decollate snail (Rumina decollata) will capture and eat garden snails, so it is sometimes introduced as a biological pest control agent.

[edit] Reproduction

Two garden snails mating

Like other Pulmonata, Helix aspersa is a hermaphrodite, producing both male and female gametes. Reproduction is usually sexual, although self-fertilisation can occur.[12] During a mating session of several hours, two snails exchange sperm. The garden snail uses love darts during mating.

After about two weeks approximately 80 spherical pearly-white eggs are laid into crevices in the topsoil. Up to six batches of 80 eggs can be laid in a year.[13] The size of the egg is 4 mm.[14]

The young snails take one to two years to reach maturity.[6]

[edit] Relationship with humans

Garden snail in Israel.

The species is an agricultural and garden pest, an edible delicacy, and occasionally a household pet.

In French cuisine, it is known as petit gris, and is served as escargot. The snails are farm-raised or bred as a hobby and eaten with garlic butter or cream sauces. Their texture is slightly chewy. The practice of rearing snails for food is known as heliciculture.

Recently, this snail has gained popularity as the chief ingredient in skin creams and gels (crema/gel de caracol) sold within the Latino community and used for wrinkles, scars, dry skin, and acne.[citation needed]

It has been introduced to many regions around the world, including southern Africa, Australia, New Zealand, North America and southern South America.[15] It was introduced to California as a food animal in the 1850s and is now a notorious agricultural pest there, especially in citrus groves. Many areas have quarantines established for preventing the importation of the snail in plant matter.

[edit] References

  1. ^ IUCN 2008. 2008 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 23 February 2009.
  2. ^ 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).
  3. ^ "The Cornu problem" (html). The Living World of Mollusks. http://www.weichtiere.at/english/gastropoda/terrestrial/escargot/cornu.html. Retrieved on 2007-03-05. 
  4. ^ Commonwealth of Australia. 2002 (April) Citrus Imports from the Arab Republic of Egypt. A Review Under Existing Import Conditions for Citrus from Israel. Agriculture, Fisheries and Forestry, Australia. Caption: Gastropods, page 12 and Appendix 2.
  5. ^ Pfleger, V. & Chatfield, J. (1983). A guide to snails of Britain and Europe. Hamlyn, London.
  6. ^ a b c Arkive: Helix aspersa
  7. ^ Ansart A., Vernon P., Daguzan J. 2002. Elements of cold hardiness in a littoral population of the land snail Helix aspersa (Gastropoda: Pulmonata). Journal of Comparative Physiology B, 172, 619-625.
  8. ^ Machin J. 1966. The evaporation of water from Helix aspersa IV. Loss from the mantle of the inactive snail. Journal of Experimental Biology, 45, 269-278.
  9. ^ Velocity Measurement Units Conversion
  10. ^ Attia J. 2004. Behavioural Rhythms of Land Snails in the Field. Biological Rhythm Research, 35: 35-41. Abstract.
  11. ^ Beeby, A., Richmond, L. (1989). The shell as a site of lead deposition in Helix aspersa, Archives of Environmental Contamination and Toxicology 18, 623-628
  12. ^ Cowie, R. H. (1984). The life-cycle and productivity of the land snail Theba pisana (Mollusca: Helicidae), The Journal of Animal Ecology 53, 311-325
  13. ^ Bezemer T. M. & Knight K. J. 2001. Unpredictable responses of garden snail Helix aspersa populations to climate change. Acta Oecologica, 22, 201-208.
  14. ^ Heller J.: Life History Strategies. in Barker G. M. (ed.): The biology of terrestrial molluscs. CABI Publishing, Oxon, UK, 2001, ISBN 0-85199-318-4. 1-146, cited page: 428.
  15. ^ UF/IFAS Featured Creatures: Helix aspersa

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