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What are those little shells on the beach that look like butterfly wings?

July 12, 2006


They are the empty shells of coquinas (Donax variabilis), small clams that live in the sand where the surf crashes onshore. This area is known as the intertidal zone.

Life is tough here, yet these little pastel-striped mollusks appear in huge patches by the hundreds, sometimes thousands. Surprisingly, their empty shells are often found intact, spread out on the sand like butterfly wings. When alive, the shells, like all clams, remain tightly closed except when feeding.


Coquinas usually measure less than an inch long and come in a rainbow of beautiful colors – lavenders, whites, tans, pale blues, deep purples and yellowish-rose. Brilliant bands radiate from the shell’s hinge, and each clam has a slightly different color pattern.


These small clams lead a life of almost ceaseless activity. Burrowing rapidly into the sand as a wave recedes, they are unearthed again when the next wave breaks on shore.

Empty coquinas look like colorful butterfly wings. (Photo by Pat Bland)


Exposed, the clam digs quickly back into the sand, using its stout pointed foot as a spade to pull itself safely undercover. Once entrenched, it extends its tiny siphons to draw in water and feed on the minute plankton carried in on the waves. It repeats this behavior hundred of times each day.


Coquinas shift higher or lower on the beach with the tides in mass movements of scores of hundreds. They seem to work an area for food, then move on. The sand flashes bright, multicolored patches, as the small clams emerge from their holes, only to be swallowed seconds later by the onrushing sea.


Birds crabs and some fishes feed on coquinas, and in some areas people harvest the little clams to make chowder. But it takes LOTS of the tiny morsels to make a meal, and the result is often more broth than clams, along with a hefty serving of sand.