On the Common Snail from BBC’s website:

Behaviour
Because of their moist skin, common snails are most active in damp weather and at night. When conditions become too dry, the snail will retreat into its shell and seal the entrance with a parchment-like barrier known as an epiphragm. Snails can often be found in this state under rocks in gardens or on a wall in a sheltered corner. When sealed away like this the snail goes into a state of suspended animation and can survive for several months without water.

Common snails feed by scraping a ribbon-like tongue covered in horny teeth called a radula, over their food. This allows them to scrape algae and lichen from the surface of rocks and walls. You can sometimes see the trails they leave behind as they eat their way through the algae on a damp wall.


Reproduction
Common snails, like all land snails, are hermaphrodites. This means that they possess both male and female reproductive organs. Despite this they still need to find another snail to mate with. When two snails meet during the breeding season (late spring or early summer), mating is initiated by one snail piercing the skin of the other snail with a calcified 'love dart'. The exact purpose of the 'love dart' is not fully understood but it seems to stimulate the other snail into exchanging small packets of sperm. After mating is complete the snails will produce eggs internally, which are fertilised by the sperm that has been exchanged.

Up to about a month after mating the snail lays about a hundred small white eggs in a nest underground in damp soil. If the conditions remain suitable for the eggs, snails will begin to hatch after about 14 days. Newly hatched snails have a small fragile shell and it takes two years for them to reach maturity.