learn only 3 things about them ...
They belong in their shells. Don't try to remove them!
Every empty shell is a potential hermit crab home. Don't
take any shells home!
other animals may live together with a hermit crab. Don't
take hermits home!
Hermit crabs are commonly seen on many of our shores. They come in
all sizes from tiny to large, and live in all kinds of shells. The
same kind of hermit crab may live in different kinds of empty shells.
Hermit crabs may live even in broken shells.
What are hermit crabs? Hermit
crabs belong a subgroup called Anomurans in the Order Decapoda.
Anomurans includes porcelain
crabs. These crab-like animals are not true crabs. True crabs
belong to a subgroup called Brachyurans within the Order Decapoda.
Empty shells are priceless! Hermit
crabs need empty shells to protect themselves, so please don't take
any shells home with you. Hermit crabs need them more than you do!
They will die without empty shells.
Features: True crabs have a hard,
shortened abdomen which they fold under their hard shells for protection.
Hermit crabs, on the other hand, have a soft, long abdomen. They have
to insert this abdomen into an empty shell for protection. The soft
abdomen is twisted to one side for a better fit into the spiral of
a shell. There are appendages at the end of the abdomen to hang on
tight to the shell.
Hermits belong in their shells: Please
don't try to pull hermit crabs out of their shells. You may rip out
their little appendages or tear their delicate abdomens.
Unlike true crabs, hermit crabs have only two pairs of walking legs.
They have eyes on long stalks to peek out of the shell. Their antennae
may be very long, or feathery. Like true crabs, hermit crabs have
two pincers. Both are used to feed with, and usually one is used to
block the shell entrance when the hermit crabs retreats into its shell.
This makes it more difficult for predators to pry them out of their
shells. In some species, one of the pincers is much larger than the
What do they eat? Many hermit
crabs are scavengers. These have a keen sense of smell to find their
food. Others eat algae and detritus.
House hunting: As a hermit crab
grows bigger, it has to find a bigger shell. A shell that is too small
provides less effective protection from predators as the hermit crabs
can't retreat deep into the shell. Hermit crabs understood the concept
of 'upgrading' long before other Singaporeans!
Before switching shells, a hermit crab will tentatively test out the
new shell first, while holding on to the old one. If the new shell
is not ideal, it instantly goes back into the old shell. A hermit
crab does not necessarily always use the same kind of shell.
Hermit crabs never kill the original occupant of the shell. They may,
however, quarrel with other hermit crabs over a desirable shell. Every
shell is a potential hermit crab home. Even a tiny broken shell or
an ugly shell covered with barnacles. One of the factors limiting
the population of hermit crabs is the availability of suitable empty
shells. So please don't take any shells away from our shores. More
about hermit crabs moving into a new shell on the wild shores
of singapore blog.
Living with a hermit: The hermit
crab makes such a comfy home in its borrowed shell that other animals
take up residence with it. These include the Slipper
snail (Family Crepidulidae), tiny
porcelain crabs and sea
anemones. These animals enjoy the constant flow of oxygenated
water that the hermit crab generates, snack on the hermit crab's leftovers,
and the hermit crab will hide in the sand or crevices where its safe
and wet so the hitch-hikers don't risk drying out.
Hermit babies: Hermit crabs have
separate genders. To mate, hermits crabs partially emerge from their
shells, releasing eggs and sperm simultaneously. The eggs hatch into
free-swimming larvae that drift with the plankton before eventually
settling down and developing into tiny hermit crabs. Some hermit crab
females may brood their eggs inside their shells.
Special hermits: Land hermit
crabs belong to the Family Coenobitidae which includes the largest
hermit crab: the Robber or Coconut crab (Birgus latro). The
Robber crab is so large that it no longer needs to live in an empty
snail shell for protection. The Robber crab is only found in the Indian
and Pacific Ocean islands. It is not found in Singapore.
Role in the ecosystem: Hermit
crabs are eaten by many animals higher up in the food chain. Bigger
crabs and birds can pry them out of their shells to eat them. Many
small animals live with hermit crabs (see above). Many hermit crabs
are scavengers and help quickly recycle dead matter on the shores.
Status and threats: The Land
hermit crabs (Coenobita sp.) are listed as 'Vulnerable'
on the Red List of threatened animals of Singapore due to loss of
our natural beaches. As for our other hermit crabs, like other creatures
of the intertidal zone, they are affected by human activities such
as reclamation and pollution as well as over-collection for the pet
trade and by hobbyists.
crabs belong on the seashore! Please don't take hermit
crabs home. And please don't buy one from a pet store. Hermit crabs
sold in a pet store are collected from the wild. Many have died during
the collection process, before they are even sold. And many of those
sold also eventually die from neglect or ignorance of proper care.
For example, within the confinement of a small tank, most die during
a moult. In the wild, they are able to find the correct place to moult,
with the proper high humidity. More
Even if they are kept alive for a long time, hermit crabs removed
from the habitat generally do not reproduce successfully. Thus, they
do not contribute to the wild population. Other animals rely on hermit
crabs as homes and as food. Removing wild hermit crabs hurts the ecosystem.
If you have bought a pet hermit crab and now feel bad about keeping
it, please do not release it on our shores. It may not be the same
species as those naturally found on our shores. It may have diseases
that may be passed on to our marine life. The least worst option would
be to return it to the pet shop where you bought it from. If you enjoy
looking at hermit crabs, why not visit them on the shore and observe
them in their natural surroundings doing what hermit crabs do?
same kind of hermit crab can live
in a wide variety of shells.
Chek Jawa Feb 07
Even a broken shell can be a hermit home.
Tanah Merah, Jun 09
hermit crabs may even live
in land snail shells!
St. John's Island, Jun 07
What it looks like inside the shell!
Even tiny Button shells are homes
to tiny hermit crabs.
Changi, Apr 05
Hanging onto the shell of a snail so recently
dead that whelks are still cleaning it out!
Tanah Merah, Feb 07
anemones may be found on
a shell occupied by a hermit crab.
Changi, Apr 07
Others may have big
Changi, Apr 07
Changi, May 11
This hermit crab is using a half broken shell.
Small 'legs' on the abdomen cling to the shell.
Keelworms may build their tubes on the shell.
Changi, Jun 05
Little animals also bore into the shell,
possibly boring sponges.
Changi, Aug 08
Unknown animal on the shell.
Changi, Aug 08
worms are sometimes seen on the shell.
Changi, Aug 08
Moult outside the shell,
original hermit crab inside the shell?
Changi, Jul 05
Transparent eyes indicates this is a moult.
Hermit crab tracks on sand.
Chek Jawa, Jan 04
Tuas, Sep 11
Moult with transparent eyes.
Tuas, Sep 11
crabs on Singapore shores
crabs recorded for Singapore
Dwi Listyo Rahayu, 2000. Hermit crabs from the South China Sea (Crustacea:
Decapoda: Anomura: Diogenidae, Paguridae, Parapaguridae)
^D. L. Rahayu. New record and new species of the hermit crab genus Diogenes Dana, 1851 (Decapoda: Anomura: Diogenidae) from Singapore.
in red are those listed among the threatened
animals of Singapore from Davison, G.W. H. and P. K. L. Ng
and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened
plants and animals of Singapore.
*from Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the
Sea: The Life and Times of Labrador Beach.
+from our observation.
Hermit crabs seen awaiting identification
are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience
sp. (Land hermit crabs)
Coenobita cavipes (VU:Vulnerable)
Coenobita violascens (VU:Vulnerable)
Paguridae (previously in Family Diogenidae)
+Pagurus hedleyi (Pink banded
- Dwi Listyo Rahayu & Rene Ong. 2 October 2015. Rediscovery of the hermit crab, Dardanus hessii, in Singapore. Singapore Biodiversity Records 2015: 145-147
- D. L. Rahayu. New record and new species of the hermit crab genus Diogenes Dana, 1851 (Decapoda: Anomura: Diogenidae) from Singapore. 10 July 2015. The Comprehensive Marine Biodiversity Survey: Johor Straits International Workshop (2012) The Raffles Bulletin of Zoology 2015 Supplement No. 31, Pp. 182-192.
- Dwi Listyo
Rahayu, 2000. Hermit
crabs from the South China Sea (Crustacea: Decapoda: Anomura:
Diogenidae, Paguridae, Parapaguridae) (pdf). The Raffles Bulletin
of Zoology 2000 Supplement No. 8: 377-404. The National University
- Dwi Listyo
Rahayu, 1996. Notes
on littoral hermit crabs (Excluding Coenobitidae) (Crustacea:
Decapoda: Anomura) mainly from Singapore and Peninsular Malaysia
(pdf). The Raffles Bulletin of Zoology 1996 44(2): 335-355
G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore
Red Data Book: Threatened plants and animals of Singapore.
Nature Society (Singapore). 285 pp.
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
- Chuang, S.
H., 1961. On
Muwu Shosa, Singapore. 225 pp., plates 1-112.
- Jones Diana
S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of
Australian Waters. Reed New Holland. 224 pp.
Helmut, 2001. Crustacea
Guide of the World: Atlantic Ocean, Indian Ocean, Pacific Ocean
IKAN-Unterwasserachiv, Frankfurt. 321 pp.
- Davey, Keith,
Photographic Guide to Seashore Life of Australia.
New Holland, Australia.144 pp.
- Edward E.
Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
Jan A., 2005. Biology
of the Invertebrates.
5th edition. McGraw-Hill Book Co., Singapore. 578 pp.