Grabbing sand with their tiny claws, the filter-feeding Sand Bubbler Crab eats detritus and plankton bits from the grains. The cleaned sand is rolled into a ball and kicked it off to the side before it gets too big to hold. Soon, the creatures are surrounded by dozens of small spheres.
One morning, on the beaches of Langkawi, I noticed fractal-like patterns in the sand. At first I thought it was caused by an impression of seaweed, but upon closer inspection, the patterns were convex, not concave – in fact – the patterns were hundreds of tiny little spheres of sand. There was always at least one clear path to a hole in the sand. If I stayed still long enough, eventually these tiny little crabs – about the size of a fingernail – climbed out of the holes and began their work.
The crabs are so small, that it is actually fairly difficult to observe what they’re doing with the naked eye.
…but their spheres leave observable patterns on the beach, indicating their presence at low tide. Filmmaker Ross Birnie captured these tiny sand ball patterns on an Indo-Pacific beach in January, 2020:
Next, watch more videos about sand, filter feeders, and crabs, including:
• Sand Bubbler Crabs make tiny sand balls
• Sea cucumbers are underwater vacuum cleaners
• The Amazing Life of Sand, a Deep Look video