Thursday, May 28, 2015

Eating sand

Sammy wears his initials, S.L.G., tattooed on his leg; this is my leg, he says, and I don't want to lose it. He`s already lost three; enough's enough.

Poor. lopsided Sammy. Only one back leg on the far side. The rest were stolen.

See his initials here?

Eating is serious business when you've got three legs and a pincer to build from scratch. And it's difficult when half your eating utensils are gone. Sammy keeps very busy these days, eating, eating, eating; no time for play. But the goodies I feed him never do him much good: the hermits steal them right out of his solitary pincer.

So he eats sand.

Bluish sand grain in Sammy's mouth. Yum, yum!

All crabs do this; so do the hermits. They pick up grains of sand, or pieces of shell, and roll them around with their mouthparts to clean off any edible algae or protein. Then they spit out the sand and grab another mouthful. It's usually a relaxed, contemplative activity, a snack between meals. Sammy makes it his meals, too.

Zooming in. Here he's chewing on bits of broken shell.

It's a good thing that crabs have such a varied assortment of mouthparts. There are brushes and holders and chewers; whatever presents itself, the crab can figure out how to eat it.

Crabs employ 6 pairs of appendages to catch, crush, manipulate, and chew food.  First in order of use are the large claws that catch, crush, and tear apart prey.  From the claws the food bits are passed to 3 pairs of outer mouth appendages, the maxillipeds.  These render and sort the bits, and then pass them to 2 pairs of inner appendages, the maxillae.  From the maxillae the food is moved to a single pair of mandibles where, after a final maceration, it is swallowed. (From A Snail's Odyssey)


  1. On the west side of Vancouver Island, Purple Shore crabs comb the sandy beaches at low tide.

    It was my first time seeing shore crabs do this above the water line (only the largest would boldly trod across the stark landscape with no retreat in sight), though I had known from documentaries that fiddler crabs do the same thing.

  2. If the sand is wet, they can disappear into it in seconds. I wonder how far away they can see a gull coming.


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