When and how do snails lay eggs?

All land snails are hermaphrodites, producing both spermatozoa and ova. Some freshwater snails, such as Apple snails, and marine species, such as periwinkles, have separate sexes; they are male and female. The age of sexual maturity is variable depending on species of snail, ranging from as little as 6 weeks to 5 years. Adverse environmental conditions may delay the onset of sexual maturity in some snails.

Prior to reproduction, most land snails perform a ritual courtship before mating. This may last anywhere between two and twelve hours. Prolific breeders, pulmonate land snails inseminate each other in pairs to internally fertilize their ova. Each brood may consist of up to 100 eggs.

Pulmonate land snails and slugs have a reproductive opening on one side of the body, near the front, through which the outer reproductive organs are extruded so that exchange of sperm can take place. After this, fertilization occurs and the eggs develop.

Garden snails bury their eggs in shallow topsoil primarily while the weather is warm and damp, usually 5 to 10 cm down, digging with their foot. Egg sizes differ between species, from a 3 mm diameter in the grove snail to a 6 mm diameter in the Giant African Land Snail. After 2 to 4 weeks of favorable weather, these eggs hatch and the young emerge. Snails may lay eggs as often as once a month.