13. The Remarkable Sleep Strategies of Snails
Those slow-moving molluscs that adorn our forests and gardens, snails have quite unusual sleeping patterns. Although their daily motions may seem ordinary, their methods of approaching long-term rest and survival are quite amazing. Two main strategies of protracted slumber that enable snails to survive in hostile surroundings have evolved: hibernation and aestivation. These apparently basic animals exhibit amazing resilience and survival instincts in these adaptive behaviours.
Many people know of the idea of hibernation, a condition of dormancy animals enter to save energy during cold winters. Many snail species follow this behaviour, therefore “sleeping” through times of low temperature when food is limited and surroundings are hostile. Snails drastically slow their metabolic rate during hibernation, therefore lowering their energy consumption to the very minimum needed for survival. This helps them to withstand severe winter temperatures that would otherwise be lethal.
But the capacity of snails to aestivate is what really distinguishes them in the animal world. Considered as the summer equivalent of hibernation, aestivation is a condition of dormancy brought on by hot and dry rather than chilly surroundings. For species of snails living in desert or semi-arid conditions, where frequent episodes of heat and drought are prevalent, this adaptability is especially vital. Snails withdraw within their shells during aestivation, secrete a coating of mucus that hardens into a protective seal, therefore shutting the opening of the shell. Considered an epiphragm, this seal stops water loss and shields the snail from high temperatures and predators.
The possible length of snail aestivation is what really is amazing. Unlike hibernation, which usually lasts a season, snails can remain in a state of aestivation for years, quietly waiting for more ideal circumstances to return. Snails are among the most robust animals on Earth since they can stop their life activities for long stretches of time and survive in conditions that would be fatal for many other species.
One especially remarkable case of snail aestivation comes from a historical narrative going back to the middle of the 1800s. One employee of the British Museum discovered what looked to be an empty shell of an Egyptian desert snail in 1846. Assumed to be nothing more than a dead specimen, the worker fastened the shell to an identity card using conventional museum procedures of the day. But four years later, in 1850, an amazing discovery was made. Unexpectedly for what was thought to be a long-dead animal, someone found signs of slime on the card.
Drawn by this peculiarity, the shell was gently taken off the card and submerged in water. Four long years of aestivation had caused a live snail to emerge from the shell, shocking everybody present. Along with the difficult conditions of its natural desert home, this snail had survived years of dormancy in a museum collection and the trip to England. The episode is evidence of the amazing survival skills of these modest organisms.
Not only enthralled the scientific community of the time, but this amazing event still fascinates scientists and nature lovers today. It begs interesting issues concerning the boundaries of life suspension and the physiological processes enabling snails to go through such protracted slumber. How may their bodies stop tissue breakdown during these protracted “sleep” sessions? After years of lethargy, how rapidly can they resume regular biological activities? What sets off their awakening?
The capacity of snails to aestivate for such long times has important consequences for our knowledge of survival tactics in hostile surroundings. It provides possible new perspectives on disciplines ranging from conservation biology to space travel, where the ability to induce long-term dormancy could prove rather useful. Furthermore, research on the molecular mechanisms allowing snails to enter and exit these phases of suspended animation may result in medical science discoveries especially in fields including organ preservation for transplantation.