Sand Crabs

A rite of passage for any kid on a sandy, ocean beach is digging for sand crabs. But you have to be in the right place. Wait in a spot where the waves will come in and wash gently over your feet. Then as the water washes back out, look for bubbles in the sand. When you see the bubbles, DIG! If you’re lucky, you’ll come up with a sand crab tickling the palm of your hand (it’s trying to burrow).

It turns out that area of breaking waves is called the swash zone. And this is where the sand crabs feed. They will move in and out with the tide, moving only backward (unlike other types of crabs that can move in any direction, these crabs can only move in one direction). Sand crabs use the claws on their hind legs, and their tails, to dig themselves into the sand backward. As a wave recedes, the crabs uncoil a set of antennae (they have two sets!). These antenna work like a net, filtering out microscopic plankton for them to eat.

Female sand crabs can lay up to 45,000 eggs (whoa!). She carries these eggs on her abdomen for 30 days until they hatch. After that she’s done, and the larvae drift off in ocean currents, which can distribute them far and wide. That may seem like a lot of offspring for one crab, but as both larvae and adults, they are food for many birds and fish.

One last thing – if you collect sand crabs in a bucket of sand, don’t leave them there too long. The sand and water heat up, which isn’t good for the crabs. Let the sand crabs go in the swash zone and watch them burrow into the sand backwards (in 1.5 seconds, apparently).