Wednesday, April 12, 2017

Hermit shenanigans

It was time to put the aquarium to bed for the night: feed the anemones, add ice, turn off the light. But in the middle of the tank, behind the anemones, a lump of waving legs and antennae turned out to be two hermit crabs, embracing face to face, half out of their shells. I ran for the camera.

I had a few seconds only; hermits don't stay in vulnerable positions for long.

Two hairy hermits (Pagurus hirsutiusculus), mating. The smaller, green legs belong to the female; the male is bigger, and has red algae growing on his hairs.

It's springtime, and love is in the air. And the water. But it's difficult for hermit crabs; to mate, they have to crawl at least partway out of their shells, exposing their soft, juicy abdomens. And crabs are always on the lookout for fresh meat. A researcher timed his hermits; copulation lasted from 10 to 36 seconds, repeated up to 4 times.

I managed to get half a dozen blurry, bubbly photos. No time to wipe down the glass first, nor to turn off the pump.

View from the top. Bubbles and swimming copepods deleted, contrast increased. The female is the one on the right; her abdomen is visible, almost entirely out of the shell.

Either she had just molted (crabs have to wait until the female molts, because of the hard carapace she's wearing normally), or she molted soon afterwards; I found her molted bits and pieces up against the glass in the morning.

I paused to wipe off the glass quickly. When I looked again, a few seconds later, both hermits were back in their shells and walking away, in different directions.

If the mating was successful, the female will be visibly in berry soon; the baby hermits will hatch in about 3 weeks. They'll be too small to see, except as moving specks in a filter, against a bright light.

I have watched the preliminary courting behaviour many times. (I reported on it here: "A friend for Boy Blue", and "Little Bo-Peep is fast asleep.") I had never managed to catch them actually in the act.

Made my day. Theirs, too, I think.


  1. Not at all voyeuristic; I have lost a lot of time watching spiders and butterflies.Usually when the camera was elsewhere...

  2. You capture so many rare occurrences. - Margy


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