The great pond snail is active all year round. In order to breathe, the snail regularly comes to the surface of the water to take in air. But in the winter – except for during especially hard frosts – the snail can also be seen near the surface, under a sheet of ice, because it can absorb oxygen through the water into its skin.
Description
Lymnaea stagnalis is one of the largest native freshwater snail species. Its shell, which is slender with a pointed spire, can grow to 54mm high and 27mm wide, and the last of the 6-8 whorls are wider and bulbous. The shell is dark brown, delicate and exhibits fine growth lines. The umbilicus around the middle of the shell is sealed.
Its typically long, flat, triangular feelers look like little horns. Well circulated, the feelers are used by the snail to breathe, taking in oxygen from the water. Like the upper side of the snail's body, these tentacles are also covered with small bright specks. The relatively small eyes are set on the bulges of the feelers. The snail's body cannot be retracted fully into the shell; the wide, oval foot must remain, unprotected, slightly outside the entrance.
Distribution
The great pond snail may be found across all of Europe and as far north as Norway. It is most commonly observed in large ponds, water-filled ditches and rivers in flatland areas. In the Donau-Auen National Park, the snail may often be found in the backwaters regularly replenished with groundwater.
Endangerment and Conservation Status
The great pond snail is not endangered in Austria and is classified as Least Concern (LC) on the IUCN Red List.
Behaviour
As the scientific name Lymnaea stagnalis would imply, the great pond snail prefers stagnant to slow-moving waters with lush vegetation and is quite tolerant of nutrient-rich environments. In its natural habitat, the snail uses its foot to crawl to the water's surface, either to feed or to replenish the air in its respiratory cavity, the latter activity lasting around 15 seconds. With the help of the air in its lung cavities, the snail is able to remain suspended in water. When threatened, the snail exhales the air quickly and can thus sink to the bottom of the pond. The great pond snail uses its rasping tongue to feed on algae, plants and all organic matter floating or sinking in the waters. It may also feed on carrion and smaller animals (bryozoa, for example). Remarkably, it may even resort to cannibalism, eating the eggs other snail species. Small stones may also be ingested in order to help facilitate digestion in its muscular stomach.
Great pond snails are hermaphrodites but are capable of self-fertilisation. The gelatinous egg masses are ribbon-like and often attached to a surface. They may be up to 65mm long and contain up to 300 eggs. Development lasts around three weeks. The great pond snail may live up to four years. If the pond should be in danger of drying out, the snail will dig itself into damp mud and can thus survive an arid period.
Special Characteristics
The great pond snail is absent from moor regions, as there is no limestone with which to form the shell.