Harry, the Hairy Hermit Crab

Say hello to Harry the hairy hermit crab (Pagurus hirsutiusculus).   Common to the intertidal zones of Alaska to California, as well as South Japan, these little guys are a friendly face you’ll be sure to encounter on the West Coast at some point or another.  In our lab we did 3 different experiments with them – but first, here are some quick facts to get to know our hairy pals before explaining our experiments:

  • They’re distinguishable by white stripes on their legs and antennae, as well as being covered in hair.
  • They’re opportunistic feeders, so they’ll pretty much eat whatever is around: detritus, seaweed, meat, etc.
  • They use the abandoned shells of other gastropods (mostly sea snails) as protection from predators. They’ll leave this shell either after growing too big for it and wanting a more spacious abode, or as an escape tactic from predators.
  • They have 2 antennules that they constantly flick in the water to smell different odours.
  • The right claw is bigger than the left and is mainly used for defence.  The left one is used for more delicate motor skills like eating or getting in a new shell and has special hairs (setae) on it that can tell what shell would make a good home.  See here for more info on how they choose shells.
Screen Shot 2017-03-12 at 7.20.36 PM

See the white bands?

To get a little more acquainted with Pagurus we did 3 experiments to see how some of their basic behavioral traits change hermit crabs kept in different temperatures and salinity levels.


First, we counted how many flicks the hermit crabs made in 30 seconds – which is easier said than done because those buggers move fast.  Here’s an even closer look of a similar species.

giphy (1)

The antennules are the 2 short middle things flicking up and down

Secondly, we cracked open some mussels and put the meat in a beaker with a hermit crab.  Over the course of 5 minutes we timed how long the individuals would spend actively eating the mussel.

And last, but not least, we coaxed hermit crabs out of their shells and timed how long it took for them to get back inside it.

The actual cajoling of the hermit crabs out of their shells was difficult at times, and took a certain touch.

giphy (2)

The best method seemed to be holding the tips of their shells and lightly shaking them very close to water. Nothin’ like the satisfaction of finally getting them to leave their shell.

giphy (3)

Anyways, the results were… drum-role please…

Not significantly different between different temperature and salinity levels for any experiment!

Average number of antennules flicks per 30 seconds: 74

Average feeding time: 0.58 seconds

Average time to return to their shell: 5.9 minutes


Although our results didn’t show any major differences in behavior between different stress levels, better understanding the possible effects of future changing salinity levels and temperature due to climate change is always important.

Next time you’re at the beach, keep an eye out for hermit crabs – will you be able to pick out Harry from the crowd?



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