One of my solar-powered garden lights has become home to a colony of snails. Typically about 20 congregrate there every day, mainly on the north face of the light (see Photo, right), but none on the solar panel. Are they adapting to 21st-century technology and using solar power to extend their periods of access to warmth and light?
鈥� The snail pictured is the garden snail, Helix aspersa or Cornu aspersum, which was accidentally introduced into England, probably in Roman times, by trade with mainland Europe. Among other habitats, it is associated with disturbed areas such as gardens and waste ground.
Avoiding loss of water is a major priority in the life of a snail, and is perhaps the single most important factor influencing their day-to-day activity and behaviour. As a result snails are essentially reclusive animals, spending much of their lives hidden away in sheltering microhabitats. Gardeners will be well aware that they can be found in abundance under bricks or stones.
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Garden snails commonly come together in places that offer some type of protection, in particular to undergo aestivation and hibernation. Aestivation is a period of inactivity in dry weather during which snails avoid losing moisture by withdrawing into their shell and adhering to a substrate via a mucous membrane. Hibernation occurs in winter and involves the shell being sealed with a calcareous plate, or epiphragm, to avoid water loss, while the snail鈥檚 pulse rate is reduced.
In the situation your questioner describes, by choosing the north side of the solar-powered light, the snails both avoid exposure to the sun and are able to shelter in the artificial 鈥渃revice鈥� afforded by the lip of the solar panel. They would naturally avoid the top surface of the panel, which is much more exposed and, of course, faces the heat of the sun.
During warmer months the snails will often be active away from the lamp, returning to their 鈥渞oost鈥� by following the chemical signals in their slime trails. At night, it is possible that the light actually provides them with some warmth. However, snails would normally avoid the desiccating heat and light given out by a more powerful lamp.
Peter Topley, Bedfordshire, UK
鈥� Snails鈥� preference for smooth, sheltered surfaces forms the basis for a good snail trap requiring no poison. Where snails are most plentiful, stand plastic flowerpots upside down with their rims raised about 25 millimetres off the ground on the side facing away from the sun. After a spell of rain following dry weather, you can collect these garden guests by the dozen for donation to grateful hedgehogs and neighbours.
Jon Richfield, Somerset West, South Africa