When nights become longer and days shorter in autumn, the Roman snail must begin to prepare for winter. Only by hibernation is it that the snail will survive the frosty temperatures of Central European winters.
At a place protected from the wind, covered with vegetation, the Roman snail begins to dig a hole in the ground. This time the snail withdraws into it, to endure winter - to hibernate. From the surrounding surface the snail pulls vegetation into the hole to further isolate it against the cold. Finally the hole is closed from inside with earth. Now the snail has to prepare to endure the frosty temperatures of winter.
First it produces a calcareous secretion from glands in the mantle fold closing the shell mouth. This calcareous secretion hardens and makes a lid, called an epiphragma, which now closes the shell mouth. The shell mouth is not closed hermetically.
Inside the shell, behind the lid, the snail withdraws further into the shell and doing so exhales. The air between the snail and the lid makes a further isolating layer.
In its winter hole frosty temperatures can do little harm to a Roman snail. In a sequence of experiments on the frost resistance of terrestrial snails it has been discovered that Roman snails can endure temperatures as low as -40°C, if the shell mouth is closed by a hibernation lid. It is, however, hard to believe, that this alone leads to such an outstanding result.
Actually there are prominent physiological changes in a Roman snail during winter. At first, the snail parts from all the water it can spare. So there is no water which potentially will freeze to form ice and to damage the snail's organism. Additionally the decrease of water raises the ratio of dissolved particles per volume blood. That way the snail produces its own antifreeze.
To keep energy consumption low during hibernation, all superfluous body functions of the snail are reduced to almost zero.
In spring, at an average surrounding temperature of about 8°C, a Roman snail's physiology returns to active state. The snail begins by breaking the membranes between the air packets and finally pushes off the lid.
When they are just awoken from hibernation the snails are famished and dehydrated. A Roman snail may recover 50% of its original weight in two days after waking up. To recover all of its weight, it will need several weeks.
Usually numerous winter lids of snails can be found in the same place - a sign that snails usually keep together, when they are hibernating.
Roman Snail while Hibernation
Roman Snail with Epiphragma
Roman Snail opening Epiphragma