Rocks that are anything but boring

By Amy Bentley

My family moved to Southwest Florida over two and a half years ago and my husband and I quickly became regular local beachcombers. This was bound to happen. I grew up in Southern California and have been vacationing in Hawaii all my life, savoring every day I could get to a beach to body surf in the ocean or collect shells at the shoreline. 

We quickly began visiting the beaches here to explore. It wasn’t long before I took my shelling hobby to the next level, combing beaches, sandbars, and barrier islands regularly at low tide to see what I might find. My husband tagged along at first to keep me company and soon discovered a beachcombing hobby of his own: collecting unique-looking rocks from the shoreline.

When he first told me he was collecting rocks to use in our home’s exterior landscaping, I looked at him doubtfully with raised eyebrows; I mean, what could be interesting about beach rocks? They didn’t have cool sea creatures or crabs in them like some of the shells I discovered, and they lacked the elaborate geometric designs of the lightning whelks I was finding. 

As it turned out, upon closer examination of these rocks, I couldn’t have been more wrong. Many were riddled with deep holes so perfectly round that it looked like they’d been drilled. Some had just one or two perfect circular holes in them and some had shell pieces embedded in the holes. Others had holes so deep, they went through the entire rock to the other side. There was no way you could chalk this up to erosion or a lucky beach find.

Our curiosity got the best of us. We turned to Encyclopedia Britannica and other online resources to learn that sea creatures—specifically boring sponges, worms, and several species of mollusks —created these holes over their lifetime. This happens to rocks found in the ocean, the Great Lakes, and on coastlines in many places around the world, not just in Florida.

Piddocks, for instance, are clam-like mollusks with serrated edges that bore themselves into rocks and create deep burrow holes. Many rocks found on the beach and riddled with perfectly circular holes are the handiwork of busy piddocks inhabiting the same rock. As they grow, piddocks grind their way deeper and wider into their hole and get stuck in it. That’s where they live for years, extending out their siphon to feed on tiny organisms in the water and then filtering out waste. When the piddock dies, its empty hole can become a home or shelter for another small sea creature like a crab, worm, or sea snail. If you find the piddock shell on the beach, it’s often called an angel’s wing, which it resembles.

My husband and I have fun knowing that the shells I collect aren’t our only beachcombing finds created by sea creatures. We use the rocks in our landscaping, mixing the best pieces with bits of various shells to create an ocean-inspired groundcover that’s truly one-of-a-kind and hand-picked just by us.

Now, while beachcombing for rocks and shells, we play a little game when we find an unusual piece that looks like it’s part rock, part shell. We’ll ask each other, “Is it a rock or a shell?” Sometimes, the answer is both.

Hagstone, Odin stone, adder stone, fairy stone, witch stone, holey stone, snake’s eggs, or...?

There are many names for rocks found with naturally occurring holes. The holes are sometimes a result of piddocks boring into the rock, but can be caused by other animals drilling into them or harder rocks or water wearing the stones. Most are found on beaches and in dry riverbeds around the world.

Myths and superstitions abound about these stones. They are said to be protective amulets when worn as a pendant or hanging in windows, doorways, or on a boat. They guard against witches, sickness, and misfortune. Looking through the hole, a viewer can spy invisible spirits, ward off curses, and see the otherworld.

No matter the name, these stones are fun to find, and they make a great place to display beach marbles and other treasures.

This article appeared in the Beachcombing Magazine March/April 2022 issue.

Learn more about beach rocks:

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