Tuesday, June 03, 2014

They've got their priorities straight

At the bottom of the boat ramp at Beach Grove, someone has laid, long ago, a series of broken paving stones, leading out across the rocks to easier walking on the sand. Every chance I get, I turn over a few of these to see what's sheltered there that day.

This time, among the usual crabs, hermits, and mud snails, I found a pair of shore crabs, either mating, or in the pre-mating holding pattern; belly to belly, male and female in a close embrace.

As I found them, jammed in between stones and shells. The male is on the left.

The other crabs around them scuttled off into crevices between the stones as soon as I removed their roof. These two just stayed put. The male wasn't going to give up his female, and she wasn't in a position to run.

Male crabs select a mature female almost ready to molt; they can't mate while she's armoured with a wide plate across her belly. In the brief moments that she is molting, out of the old shell and unprotected, she may be impregnated. So once he's found a mate, he holds on and doesn't let go until she's ready.

I took a few photos, moving around to get better lighting. Neither crab moved. So I gently eased them out of their cubby-hole. They didn't move, even in my hand. So I placed them on the upside-down paver. Again, neither of them attempted to leave.

The male is on the bottom, this time. Mature males have large pincers and go around posturing with them; "Look at me, look at me! I'm big and I'm dangerous!"

Before they got sunburnt, I slid them off the edge of the slab and back into their cozy hideout. And there, they got down to their interrupted business.

The female is on top this time. A curious hermit - aren't they all? - watches from the bottom of the photo.

The female's apron, the wide abdominal plate, is finally opening. She will be backing out of her old carapace any minute now, leaving the hard forms of legs, eyes, pincers and all behind, taking the soft parts except for her esophagus, stomach lining, and part of her intestines; she'll have to make new ones. And as soon as she's free, the male will impregnate her eggs.

After that, he'll leave; the eggs will develop under her apron, where she'll fan them, clean them, and exercise them until they're ready to hatch, up to eight months from now.

An old video of a mother in berry is on YouTube. (It doesn't work as well as it used to; I'll have to remake it, and a whole bunch of other oldies.)


  1. You find the most amazing creatures!!! And I always learn something when I visit you!!!

  2. Are you saying she has to grow new lungs or am I misunderstanding? If so, how does she breath while they are growing?

  3. Lucy: Oops! I was half asleep, I think! She takes the gills (not "lungs"; I was really out of it) and leaves behind a "ghost gill", the empty shape where the gills were. What she leaves behind are the esophagus, the stomach lining, and the tail end of her intestines. I don't know how, or if she eats until she grows those back.

    I've corrected the post. Thanks for alerting me!

  4. Those photos are phenomenal.


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