Snails Build Homes

            Do many animals build homes?  Mollusks do. And snails are a type of mollusk that make homes for themselves and for other animals, too. They make hard, mineralized shells out of calcium carbonate (CaCO₃).

At one of our field sites there is almost a carpet of shells

How much calcium carbonate do they produce? One team of biologists (Gutierrez et al., 2003) studies this idea that mollusks shells create habitats for other animals. They calculated how much they produce and found that marine mollusks may produce 50-1000 grams CaCO₃/meter/year.  Let's put that in context.  If you compare the calcium carbonate production of mollusks to the wood production of trees, they that “…persistent structure is produced by mollusks at rates comparable to trees”!

It’s easy to see the construction of habitats in action. Snail shells can be found on most beaches. Sometimes they contain the living snail. You might see their bodies in their shells, or you might see them crawling around. Other times, the snail has died and the shell is empty. If it’s intact, an empty shell can become a home to other small animals. 

Some slipper limpets living inside this moonsnail shell

Hermit crabs are a type of crab that occupies empty shells for homes, “moving in” when they need a home (see how to get hermit crabs out of the shell). Other snails can occupy vacant shells, too.  Small sponges and worms often burrow into the shell material.  Some fishes even use clam shells and oyster shells as nests for their eggs.

So, the next time you see a shell, imagine all the little animals that may have lived in it. Hooray for snails: they build homes and create communities!

by Nina Dropcho,

Collin Lab, past STRI intern