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A Roman snail digging the hatchery hole. Photo: Robert Nordsieck.

A Roman snail laying eggs. Photo: © Klaus Bogon. Enlarge!

About 4 to 6 weeks after mating, usually from late June to August, Roman snails often undertake longer migrations in search of a suitable place to lay their eggs. For constructing the hatchery, they require at least 3–5 cm of loose soil in which they can dig a hole.

Similar to the one it uses for hibernation, the Roman snail digs this earth hole for oviposition by movements of its foot, using the shell as support. Not every earth hole the snail begins is actually used for laying eggs; often the snail abandons one attempt and starts again at another location.

Only after successfully completing a suitable hole does the snail, during a resting phase of several hours, begin with the fertilisation of its eggs and the subsequent preparation of the eggs in the oviduct.

However, egg-laying is an involuntary process that, once started, the snail cannot interrupt intentionally: if it is disturbed, for example, it will simply continue laying elsewhere, even if this means that the eggs are deposited on the soil surface.

At intervals of 15 to 30 minutes, the Roman snail lays one egg after another, each measuring about 6 mm and weighing about 0.1–0.2 g. A batch can contain between 40 and 60 eggs, depending on the snail’s age and location. The laying process may last 20 to 30 hours, during which the snail does not leave the hole.

After it is finished, the snail withdraws the anterior part of its body from the cavity and crawls across its opening to seal it with soil particles. The development of the young snails now proceeds inside the sealed hole without any further involvement of the parent.

True brood care in molluscs is only found among the most highly developed specie: the octopuses.

Juvenile Development.