Saturday, March 06, 2010

Do they bite?

"I found a crab!" Three little boys, about 5 to 10 years old, were digging among the rocks on Centennial Beach the other day. "I found a crab!" the littlest one shouted again.

"Does it bite?" his brother asked.

No.  And it probably won't pinch. Not hard, anyhow. But the boys crouched there, poking gingerly at it with sticks. Such excitement! Such danger!

I remember. I was a kid, teasing crabs with a twig, long ago. And I still feel a bit of that excitement when I turn over a stone and a green shore crab dares me to "Come on!"

Looking for more crabs. Well armed.

Most of the crabs we see on the beaches are either dead or the cast-off molts. Live ones usually scuttle off under a rock or a knot of weed. We don't get much of a chance to count the "teeth" or compare the shapes of pincers.

But I still bring crab shells, and sometimes whole dead crabs, sun-dried, home. I have bowls and trays and shelves full of them. So I decided to count their teeth, for practice.

The crabs most accessible to us in the upper intertidal zone of the Lower Mainland are the shore crabs, green and purple. They show up just below the high tide line, mostly hiding underneath stones in rocky areas.

Two very small green shore crabs. The large one measures 1/4 inch.

The green shore crab, Hemigrapsus oregonensis, has a rectangular carapace and tiny hairs on the walking legs. (On these two, I could see them with the hand microscope.) It grows to about 2 inches across the carapace. Juveniles can be any colour from deep red to green, to white.

Another green.

And a purple shore crab carapace, with the broken pincer. And polka dots!

The purple shore crabs look like the greens; they may be green, too. But the legs are never hairy, and the pincers have red dots. (Unless the crab is green; then it's only the hair that separates them, and you may not see that on the beach.) Two other characteristics I don't find in the books, but see on the crabs, all colours, are the three teeth along each side of the front, and the smiley face in centre back, looking at them from the rear.

Dungeness crabs may be green, too, although the books say "reddish brown to purplish".

Reddish brown Dungeness, Cancer magister, with purplish tints.

The Dungeness is a large crab, growing to about 11 inches across the fan-shaped carapace. This one measured 6 inches; that's usually about the size of the big shells we find, mostly on the White Rock or Boundary Bay beaches. They like wide, sandy beaches, with few rocks.

We see the live ones only at low tide. Even then, they're difficult to see, since they bury themselves almost completely in the sand. I have looked at one for up to a minute without seeing it, then suddenly the shapes resolve themselves and I notice the eyes, watching me intently.

Here's where we count the teeth. The Dungeness has ten "teeth" on either side of the eye, ending at the wide point of the carapace.

"Teeth". Only the little white bumps on each paddle count as teeth; tooth, bump, bump, bump, and a valley.

The pincers are long and strong; be careful handling a live one! Pick it up from the top of the back, not the hindquarters; they can reach you there with the pincers.

Pincer. More "teeth". Sort of looks like locking pliers (vise grips). The tips are white or whitish.

Live Dungeness, underwater, on Centennial Beach at lowest tide. This one's more green than red. The pincers are white-tipped.

The red rock crab, Cancer productus, is similar to the Dungeness, and almost as large, up to 8 inches across the shell. They can be found on many types of beaches, from sand to gravel to rock, in quiet waters or strong waves, shoreline to deep underwater. I find it strange that I have only seen one, a tiny one, on the beach in Campbell River. I do have a pincer that I picked up on the White Rock beach, though:

These pincers are thick and strong, with black tips.

On websites with crab recipes, I find repeated warnings about these crabs; they are likely to attack, and their claw can cut through strong work gloves.

The red rock is the same general fan shape as the Dungeness, and more or less a similar colour. The distinguishing feature, again, is the teeth along the edge of the carapace. Instead of 10, as in the Dungeness, they have 9. (Try counting them while the crab hides under the seaweed and snatches at your toes!) In between the eyes, the shell makes 5 peaks. So does the Dungeness, sometimes; I have one with only 4.

It will be easier, when I see my first big live one, to check the rim of the carapace. It is fluted, like the wavy pie crusts I used to make.

One other shell I have, one that I can't remember where I found it, is from a kelp crab;

Small shell, about 2 inches long, sun-bleached.

This is a long-legged crab that lives in kelp beds. Kozloff lists it among the most common crabs in this area, but it's most likely to be found underwater at extreme low tide, in the eelgrass. It will be a dark olive green. Another critter to look for.


  1. Amazing information and pictures! I love how you see the very smallest of details. There is beauty in the tiniest of God's creatures, thank you for helping me see this!

  2. WOW!! Amazing post. I'll have to go back and read it again. And probably again. Thanks for all the info!! ~ks

  3. Anonymous5:17 pm

    Wanderin Weeta-
    Wonderful crab photos!
    Wonder if it would be possible to use your photos of the hiding Dungeness and also the Red Rock Crab for an educational interpretive sign for the Mission Creek Conservancy in San Francisco? You will of course be credited.
    Let me know
    Many thanks


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