Some snails can sleep for three years straight to survive without water.

In 1846, a desert snail from Egypt was sent to the British Museum in London. A scientist named Dr. William Baird thought the snail was dead and glued it to a display card. Four years later, staff noticed fresh slime on the shell and put it in warm water. The snail woke up and crawled away after four years of sleeping!This long sleep is called estivation. It is like hibernation, but for hot and dry weather instead of cold weather. To stay safe, the snail makes a hard door out of dried slime and calcium called an epiphragm. This door locks moisture inside the shell so the snail doesn't dry out like a raisin.While sleeping, the snail's body works very slowly. Its heart rate drops and it uses 80% less energy than usual. It stops eating and slowly uses up stored fat to stay alive. Researchers found that some snails can even survive heat over 40 degrees Celsius (104 degrees Fahrenheit) while in this state.The snail stays asleep until it rains or the air gets very humid. The water softens the slime door, which tells the snail's brain that it is safe to come out. Scientists have studied snails like the Otala lactea to see how they turn their body functions on and off like a light switch.