How a snail turns calcium into shell
A snail’s shell is living equipment, but it is not made of living tissue. The soft mantle—a layer of tissue beneath the shell—adds new shell material, largely calcium carbonate, as the animal grows. Calcium from food and the environment supplies a key ingredient for that process.
That is why a snail may rasp at mineral-rich ground or a discarded shell with its tongue-like radula, a flexible strip covered in tiny teeth. The scraping loosens material the snail can swallow; digestion makes some of its calcium available to the body.
Growth and repair depend on a steady supply
A snail’s shell grows mainly at its opening, where the mantle extends it. Calcium is also useful when the shell is damaged: if the mantle remains intact, it can secrete material over a break. Repair takes resources, though, and a shortage of available calcium can make shell growth more difficult.
The need is especially visible in young, growing snails, which must add shell as their bodies enlarge. A calcium-rich patch of soil or an old shell can therefore be more than a convenient snack—it is a source of raw material for protection. What looks like a snail eating a piece of another shell is, in effect, gathering supplies for its own.
