Great pond snail  (Lymnaea stagnalis)

Common and widespread in England, scarce in Scotland and Wales (2).

This species is the largest pond snail in Britain (1). It has a shiny yellowish brown shell, with a tall, slender and pointed spire (2). The shell walls are delicate and fairly transparent; they have fine markings, more prominent growth lines and variable dents on the surface (2). This snail's body is yellowish grey in colour, with a large head and long, flattened tentacles (3).

This pond snail is common in England but becomes scarce in Wales and Scotland. The distribution may be affected by the introduction of this species to garden ponds (1). Elsewhere, it is found throughout Europe, northern Asia and North America (2).

Found in still or slow-moving waters where there is plenty of aquatic vegetation (2). As the specific part of the Latin name, stagnalis suggests, this species prefers stagnant water (4).

This species feeds on both plant and animal matter with a rasping tongue known as a radula, which can leave distinctive feeding marks behind (5). It can even attack newts, small fishes, and water beetle larvae and may occasionally be cannibalistic, eating smaller great pond snails (3). It lays large gelatinous egg-masses on weeds and other objects in the pond (4). These egg masses measure between 5 and 6 cm in length (6), and can contain as many as 50-120 eggs (4). The size to which a specimen will grow is dependent upon the volume of water in the pond; individuals grow larger in big ponds. Young specimens are slender and have more translucent shells than mature snails (4).

Great pond snails often come to the surface to take in air into a respiratory cavity. When the pond becomes covered in ice, or when the snails move to deeper water in winter, they are able to take in oxygen from the water through the skin. The wide tentacles play a key role in the intake of oxygen; the surface of the tentacles is covered in tiny hair-like structures known as 'cilia' which function to increase their surface area, thus increasing the intake of air (7).

Not currently threatened.

No conservation action has been targeted at this species.

For more on invertebrates and their conservation see Buglife, the Invertebrate Conservation Trust at:
http://www.buglife.org.uk/

• Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Radula: in some molluscs, a narrow structure that bears teeth and is used to rasp at food.

1. National Biodiversity Network Species Dictionary (March 2003): http://www.nhm.ac.uk/nbn/
2. Pfleger, V. & Chatfield, J. (1983) A guide to snails of Britain and Europe. The Hamlyn Publishing Group Ltd., London.
3. Step. E. (1951) Shell life: an introduction to the British mollusca. Frederick Warne & Co. Ltd., London.
4. Nichols, D., Cooke, J. & Whiteley, D. (1971) The Oxford book of invertebrates. Oxford University Press, Oxford
5. Sterry, P. (1997) Complete British Wildlife photo guide. Harper Collins Publishers, Ltd., London.
6. Olsen, L., Sunesen, J. & Pedersen, B. (2001) Small freshwater creatures. Oxford University Press, Oxford.
7. Janus, H. (1982) The illustrated guide to molluscs. Harold Starke Ltd., London.