Helix aspersa

Helix aspersa
Helix aspersa
Conservation status
NE[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Heterobranchia informal group Pulmonata clade Eupulmonata clade Stylommatophora informal group Sigmurethra
Superfamily:	Helicoidea
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 species of land snail, 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.

Distribution

A hibernaculum on a doocot in Eglinton, Scotland

This species 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.

It comprises a set of north African endemic forms and subspecies that were described at the beginning of the 20th century on the basis of shell characteristics. The most common one, Cornu spersum aspersum (synonym Helix aspersa aspersa), has become very abundant in all man-disturbed habitats in regions with a Mediterranean, temperate and even subtropical climate.^[5]

Cornu aspersum is a typically anthropochorous species which is nowadays widespread throughout the world in many zones with climates differing from the original Mediterranean one. Its presence is reported on the American continents, as well as in Australia and in Asia. Therefore, the first explanation for resemblances between populations located on either side of the Mediterranean could be passive transport due to human activities. Transfers might have started as nearly as the Neolithic revolution (around 8500 BP) and nowadays they continue occurring in giving rise in some cases to catastrophic destruction of habitats.^[5]

It is very widely introduced and naturalised elsewhere in the world^[6][7] and its non-native distribution include other parts of Europe: Bohemia in the Czech Republic since 2008;^[8] southern Africa, Australia, New Zealand, North America and southern South America.^[9] 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.

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.^[10] During aestivation, the mantle collar has the unique ability to change its permeability to water.^[11] 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 octopuses.

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.^[7] It moves at a top speed of 1.3 centimetres per second^[12] (47 meters per hour or ~50 yards per hour),^[13] and has a strong homing instinct, readily returning to a regular hibernation site.^[14]

Ecology

Helix aspersa

The garden snail is a herbivore and has a wide range of host plants. It feeds on 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.

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.^[15]

Reproduction

Mating Helix aspersa.

Like other Pulmonata, Helix aspersa is a hermaphrodite, producing both male and female gametes. Reproduction is usually sexual, although self-fertilisation can occur.^[16] 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.^[17] The size of the egg is 4 mm.^[18]

The young snails take one to two years to reach maturity.^[7]

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.

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.

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

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.

References

H. aspersa shell cemetery. Individuals failing to overwinter in Scotland.

This article incorporates CC-BY-2.0 text from reference ^[5].

External links

• brown garden snail on the UF / IFAS Featured Creatures Web site
• Canada Agriculture Fact Sheet
• BBC Info Page
• Pesticides Database - Chemical Toxicity Studies
• Extreme Close-Up Video of the North American Garden Snail