Ocean Watch

Monday, November 30, 1998

Crabs’ fearsome
looks are almost
all for show

Last week, I took my friends' 5-year-old boy for a ride around the Ala Wai Boat Harbor on the back of my kayak. My passenger was having a great time, chatting up a storm, when we turned the corner of the breakwater. Suddenly, there was silence.

"What's wrong?" I asked.

"Let's go back."

"But there's a nice little beach over here. We can get out of the kayak and play there."

"Where's my dad?" my young friend said. "I want to go back."

I turned to look at him. His eyes were wide as he stared at the black rocks of the breakwater, a few feet away.

"Mathew, tell me what's wrong."

His lip quivered. "I'm afraid the crabs will bite me."

I looked at the rocks again. They were covered with black rock crabs, basking in the sun. I nodded, understanding Mathew's fears perfectly. When I first moved to Hawaii, I too was afraid of crabs.

It's not an unreasonable fear.

Crabs are scary-looking creatures that look a little too much like spiders for most people's comfort. (Once a visiting friend thought the rock crabs near my boat were tarantulas.)

But even though crabs look formidable, their pluckiness is almost all show.

The crab parts that instantly grab people's attention are the animals' front pincers or claws, a large pair of legs heavier than the others. A crab uses these enlarged claws for several purposes.

One is to defend itself. If threatened or cornered, many crabs will turn on their predators and boldly raise their "fists."

In some species, these fist-claws can pinch or even cut human skin. However, contrary to what I once believed, crabs would much rather run than fight. They do not seek out waders to tweak their toes, nor do they roam the beach looking for tender skin to pinch. A crab injury almost always comes from someone trying to corner or catch a crab, in which case the animal is fighting for its life.

Crabs claws have other uses. Mainly they are tools for tearing off chunks of food, usually dead animals on reefs, rocks and beaches. Once a piece of food is torn off, the crab transfers it to its mouth, where three busy pairs of external jaws work on breaking it into even smaller pieces.

Some crabs use their pincers in creative ways. Hawaii has one small species called the anemone crab which carries stinging sea anemones in its claws. When a predator threatens the little crab, it raises its anemones like a pair of boxing gloves.

Another species of hermit crab is a masseuse. This crab takes advantage of anemones' stinging potential by allowing these animals to grow on the outside of its shell.

When the hermit transfers to a larger shell, it uses its front claws to gently massage its anemones. This causes them to move to, and thus protect, the hermit's new home.

Other crabs also use their pincers during a move. Some species have tiny hooks on their backs that hold foreign objects, such as sponges and seaweed. When these crabs molt, they carefully pick their camouflaging material from the old shell and place in on the new.

Not all crabs have pincers that can hurt human skin. Last week, I found a 3-inch-wide offshore crab stranded ashore in a tangled net. I picked up the creature, carried it to the water and turned it loose. But I wasn't just being brave: I knew this species had small, weak pincers.

Eventually, I convinced Mathew that the rock crabs would never, ever jump off those rocks and swim over to the kayak to pinch us. Later, when we were back at my sailboat, he shouted.

"Dad, I saw rock crabs!"

"Did you like them?"

"Yes. Can I have a kayak for Christmas?"