a snail with a drill

When I was young I was lucky enough to spend my summer holidays at my grandparents' beach house. I suspect that these wonderful childhood summers have greatly influenced my life because 40 years on I still spend a great deal of time exploring the shore and under the waves. Doing so I often find things that take me back to those carefree summer days and the delights of discovery.

One such memory is of collecting small bivalve shells with what appeared to be neat drill holes. The purpose in collecting the drilled bivalves was, wait for it, to thread the shells onto fishing line to make necklaces.

Some may say "not a very blokey thing to do" but I was very young, or perhaps I could claim I was making the necklaces for a girlfriend. Whatever.

bivalve shells
Four bivalve shells, each with
a neatly drilled hole
(click thumbnail for full image)

Conical Sand Snail
An illustration of the Conical
Sand Snail Polinices conicus
(from my book Australia's Southern Shores - email Harry to purchase a copy)
(click thumbnail for full image)

At that time in my life I often wondered how such neat holes came to be drilled in the bivalve shells. I discovered the answer by reading John Child's wonderful little book Australian Sea Shells (I still have my 1961 edition). The drillers are the same sand snails that lay their eggs in sausage jellies and sand collars. I speak of sand snails that belong to the genus Polinices.

These sand-dwelling snails feed on bivalves that also live in the sand. They do so by using a coiled tongue, called a radula, to drill through the bivalve shell. Once the hole is drilled, the sand snail quickly kills the bivalve then devours its soft flesh. This leaves the empty bivalve shells to wash ashore, often in great numbers.