Give a sand bubbler crab some sand and you won't believe what it'll rustle up for you!

After a three-hour minibus trip down the coast, to a town called Hua Hin in the northern part of the bay of Thailand, I finally found myself on a beach. It was 4am (still dark) and also overcast, which didn't bode well for the sunrise photos I had planned. There were a few other people around, but no other photographers – maybe they knew something I didn’t. I had a feeling I was in for a wasted trip when something caught my eye. Low tide had now reached its peak and the beach looked odd, like someone had raked it. Closer inspection revealed the tiny culprits.

The beach was covered by millions of tiny spheres of sand, all created by the sand bubbler crabs (or Scopimera). Why? Because they're hungry.

Basically, the tiny balls are a byproduct of the crabs' snacking. They don’t eat the sand, but they do feed it through the bottom of an adapted mouth of sorts, filtering out all of the micronutrients that the high tide has brought in and dumped on the beach since their last feeding session. The crabs retreat into small burrows in the sand during high tide, and emerge every low tide to feed. You can actually see small trails that lead back to their burrows, with the little balls stacked up on either side.

Getting close enough to the critters was pretty difficult, and generally I had to pick a spot and wait patiently for them to come out. Being so small and numerous, they face a long list of dangers, including the local birds, larger crabs, the occasional careless beachgoer – and even their own kind (
I watched one crab drag another into its burrow and then seal it up ... presumably to do something sinister without needing to worry about its neighbours’ prying eyes).

Sand Bubbler Crab Rolling Up Sand Grain 07 03 2014
The tiny crabs sieve nutrients from the sand, regurgitating the rest in the form of these small pellets, which they deposit on the beach. Image: Brett Blignaut, BRB Photo
Sand Bubbler Crabs 07 03 2014
Given enough hungry crabs, the beach soon becomes littered with their sandy deposits. Image: Brett Blignaut, BRB Photo
Sand Bubbler Crab At Burrow Entry 07 3 2014
Come high tide, the crabs retreat into their burrows, where they wait for their next feeding session at low tide. Image: Brett Blignaut, BRB Photo
Sand Bubbler Crab Trails 07 03 2014
And this is what all that furious feeding action creates … countless tiny pellets surrounding the small openings of the burrows, with a telltale trail left by the crab. Image: Brett Blignaut, BRB Photo
Flies Eating Dead Sand Crab 07 03 2014
Sadly, not all of the crabs make it back to the safety of their burrows. This unlucky crustacean was crushed by an unobservant beachgoer - and it's now become a tasty snack for others. Image: Brett Blignaut, BRB Photo

For a great video of sand bubbler crabs in action in Malaysia, click here.