Hermit Crabs with Sponge Homes
Please see photo below.
You are looking at two animals, not one.
Alaskan Hermit Crab = Pagurus ochotensis to 5.3 cm long. The yellow eyes and “sheen” on the legs help in IDing this species. See how uniquely reflective the legs are? This species often lives in a shell made by a Northern Moon Snail (until a suberites sponge dissolves it away 😉 ).
This is an Alaskan Hermit Crab (who resides in front of Port McNeill, not Alaska).
Living on his/her back is a “Hermit Crab Sponge”.
This sponge species (Suberites latus) settles on the shell home of some hermit crab species and can completely dissolve the shell away.
Having a sponge home has its advantages. It is light. Also, the sponge will grow whereby the hermit crab need not find a new home as would be the case if it outgrew a shell home.
But, it can be awkward to tote around when it gets really big. See an example below.
Bering Hermit with a huge suberite home relative to its size. (Pagurus beringanus to 2.6 cm).
Yes, the hermit crab could leave the sponge and get another home if one were available. But, there is risk when outside your home, be it ever so brief.
Another disadvantage is when you have unwelcome house guests.
See below to get a sense of the inconvenience when a sponge predator crawls on your back.
Close-up on the inconvenienced Mud Hermit Crab.
From top to bottom: the big yellow animal is a Monterey Dorid (nudibranch species – gills are on left). This nudibranch is feeding on the Hermit Crab Sponge (tan colour) and then, see the tiny face? That’s a Mud Hermit Crab who isn’t going anywhere for a little while (Pagurus capillatus to 4 cm).!
Here’s another Mud Hermit Crab. See the bite out of the sponge? I initially found this individual upside down. The resulting photo of the underside of the sponge gives you a sense of how the sponge is shaped to the hermit crab’s body.
Note too how all the hermit crabs included in this blog have one claw bigger than the other? This is the case for many hermit crab species and it allows them, when they retreat into their home, to seal off the opening to the shell or sponge with the bigger claw. They close the door to their home.
In the photo below, see how the larger claw seals off the hole for the hermit crab on the right? I suspect this interaction captured in this photo more about mate selection that it is about home envy.
I hope this “who is sponging off who” interaction provides some wonder for you at a time when safety in homes is such a reality for our species too (re COVID-19).
Be safe whatever, and wherever, your chosen home. 💙
The Hermit Crab Sponge is Suberites latus to 20 cm long, 6 cm wide and 4 cm high.
Source for these dimensions is “Beneath Pacific Tides” by Greg Jensen.
Bluespine Hermit with sponge home (Pagurus kennerlyi to 3.5 cm long)
Juvenile Alaska Hermit who will benefit from the sponge growing bigger.
Bering Hermit Crab interaction. This too is more likely about dragging around a potential mate.
The Marine Detective 
2 Responses to “Hermit Crabs with Sponge Homes”
Hi Jackie,
We love the story ‘Pagoo’ so it was really fun to see all these other kinds of Pagurus. Love from Amanda, Ava and Andrew
How wonderful to hear from you and you just made the writing of the blog VERY worthwhile.
Love back to you on Hornby Island Amanda, Ava and Andrew!