Hermit Crabs
© 2005 Mary Jo Adams
When I ask the kids at Rosario Beach (at Deception Pass State Park) which critter is their favorite, they often tell me it's the hermit crab. It's easy to figure out why kids and adults love hermit crabs. Their antics in the tide pools are certainly entertaining.
I'll bet you didn't know that some hermit crabs are terrestrial. One amazing species (Birgus latro) can climb coconut trees, cut a coconut loose, and can make a hole in a coconut so it can eat the inside! (I'm not making this up!) They do all have to return to the water to reproduce however.
Did you know that hermit crabs are not considered true crabs? Two big differences are seen in the legs and the antenna. True crabs have 5 visible pairs of legs. The first pair are the claws and the other four pair are walking legs. In hermit crabs, the first pair are the claws but there are only two pairs of walking legs. The other two pair are used to hold it in the shell it occupies. True crabs have two pairs of antenna and they are located between the eyes. Hermit crabs have two pair of antenna but only one pair located is between the eyes.
Here in Island County, we commonly see two species and there is one other to watch for. The hairy hermit crab (Pagurus hirsutiusculus) is fairly easy to identify. It's usually very hairy, has antenna that are alternately dark and light banded, and it has white or blue bands around its walking legs. In addition, this species is often in a shell that seems a couple of sizes too small. This use of an undersized shell gives it increased mobility. These little fellows are found higher in the intertidal area. Watch for them in tide pools, under rocks, and under clumps of seaweed. They're very common here.
Lower in the intertidal, you'll see the granular hermit crab (Pagurus granosimanus). It has red or orange antennae, lacks hair, and its claws seem rough or grainy. This hermit crab will pick a shell it can pull its entire body back into. I saw both P. hirsutiusculus and P. granosimanus in the same tidepool at Rosario recently.
A third species to watch for is Pagurus beringanus. This species is usually subtidal but may occasionally be seen in very low subtidal areas. It has green eyes and red bands on its legs.
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