Garden Snail, Helix aspersa
The Garden Snail (Helix aspersa) is a species of land snail, a terrestrial pulmonate gastropod mollusk belonging to the family Helicidae, the typical snails. This species is one of the most famous of all terrestrial mollusks.
It has been placed in the genus Helix, in all sources between 1774 and 1988, and in most sources until rather recently. But in numerous sources since 1990, this species has been placed in one of three other genera, depending on the classification in relation to Helix aperta and on the accepted interpretation of the ICZN Code’s Article 1.3.2 for the Cornu issue.
Although this species can be eaten, it is frequently regarded as a pest in gardens and to agriculture, especially where it has been accidentally introduced. It’s native to the Mediterranean area and western Europe, but has been distributed by humans, both deliberately and accidentally to a number of areas all over the world.
Its native distribution to the Mediterranean region and western Europe, from northwest Africa and Iberia east to Asia Minor, and north to the British Isles.
It makes up 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 common in all human-disturbed habitats in areas with a Mediterranean, temperate, and even subtropical climate.
An adult individual has a hard and thin calcareous shell measuring 25 to 40 millimeters in diameter and 25 to 35 millimeters high with 4 or 5 whorls. The shell is rather variable in coloration and shading but is usually dark brown or chestnut with yellow stripes, streaks, or flecks.
The body is soft and slimy, colored brownish-grey, and is entirely retracted into the shell when the animal is not active or is threatened. During cold and dry weather, the aperture of the shell is sealed with a thin membrane of dried mucus which is referred to as an apiphragm, which aids in retaining moisture. The resultant quiescent periods are referred to as aestivation and hibernation respectively. While hibernating, H. aspersa avoids ice formation by altering the osmotic components of its blood and can survive temperatures as low as -5 degrees Celsius. During aestivation, the mantle collar has the special ability to change its permeability to water. That, combined with an osmoregulatory mechanism much like that seen during hibernation allows H. aspersa to survive several months of aestivation.
During times of activity, the head and the foot will 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 retract into the head. The mouth is found beneath the tentacles, and contains a chitinous radula which the snail uses to scrape and manipulate particles of food.
The garden snail is a herbivore and has a wide range of host plants. It consumes numerous types of vegetable crops, fruit trees, cereals, and garden flowers. It is a food source for many other animals, including mammals of small size, many species of birds, frogs, centipedes, lizards, predatory insects, and predatory terrestrial snails.
This species can be utilized as an indicator of environmental contamination, as its shell acts as a site for deposition of toxic heavy metals such as lead.
H. aspersa is a hermaphrodite, producing both male and female gametes. Reproduction is normally sexual, although self fertilization can happen. During a mating session lasting several hours, the two snails exchange sperm. The garden snail uses love darts while mating. After roughly two weeks, about 80 spherical pearly white colored eggs are laid into crevices in the topsoil. Up to six batches of 80 eggs can be laid in the period of one year. The egg measures 4 millimeters. The young snails take one to two years to achieve maturity.
Image Caption: A Snail (Helix aspersa) in Balboa Park. Credit: Jon Sullivan/Wikipedia