Helix aspersa

Appearance

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 color 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, and can survive temperatures as low as -5°C. During aestivation, the mantle collar has the unique ability to change its permeability to water. 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.

Distribution

This species is native to the Mediterranean region 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 aspersum aspersum", has become very abundant in all human-disturbed habitats in regions with a Mediterranean, temperate and even subtropical climate.

"Cornu aspersum" is a typically anthropochorous species; in other words this species has been spread to various geographical areas deliberately and /or accidentally by humans. It is nowadays widespread throughout the world, and occurs in in many zones that have climates differing from the original Mediterranean climate in which it first occurred. Its presence is reported on the American continents, as well as in Australia and in Asia. Because of this fact, the most likely explanation for resemblances between populations located on either side of the Mediterranean would be passive transport due to human activities. Transfers involving this species may have started in the Neolithic revolution. In the present time these introductions continue to occur, and in some cases give rise to catastrophic destruction of habitat.

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

Behavior

Like other Pulmonata, "Helix aspera" is a hermaphrodite, producing both male and female gametes. Reproduction is usually sexual, although self-fertilisation can occur. 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. The size of the egg is 4 mm.

The young snails take one to two years to reach maturity.The snail's muscular foot contracts to move the animal, and secretes mucus to facilitate locomotion by reducing friction against the substrate. It moves at a top speed of 1.3 centimetres per second,...hieroglyph snipped... and has a strong homing instinct, readily returning to a regular hibernation site.

Habitat

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.