For
each crab I have a few shells which are just a little bit bigger
than their existing shell. When the crab moults (approximately
once a year) they need a choice of shells to move into. The
change in body size may be small but it will be important that
your growing crab needs a choice of shells. They will be very
crabby if they do not have bigger shells for bigger bodies.
Upsizing Before
A Moult
Sometimes
hermit crabs will change into a bigger shell just before they
moult. Often these hermit crabs have spent a long time in the
salt water pond and their abdomens have swelled just as our
feet do when on long car or bus/coach journeys. You may have
felt your feet feel
swollen and cramped within your shoes. That must be how your
hermit crab must feel when they have drank a lot of water from
the fresh water dish or their salt pond. They need to go through
this process so that they can burst their exo, then slip free.
I guess it is a little bit like when you are young and your
feet grow so fast that you often have them split or come apart
at the seams.
What To Look For
When Selecting Suitable Seashells
When selecting
shells, it is important to find seashells that are suitable
for your hermit crabs. The rule of thumb is to have three shells
per hermit crab, including:
- one the same
size as the one your hermit crab is currently in, both in
aperture (opening) and perhaps in width/length. It may be
the same shell species/type or one of the more popular seashells
so that you maximise the chance your hermit crab will be happy
in their new shell
- one slightly
smaller than the one your hermit crab is currently in, especially
if the shell they are wearing is sliding and they have poor
control of it, OR they are obviously tiny within a large shell
- one slightly
bigger than the one your hermit crab is in, in case they need
more room pre/post moult or their own shell is too small for
them
You look
for any holes or cracks that could cause the hermit crab to
dehydrate from drained shell water. Hermit crabs use not only
to keep their gills moist so that they can breathe, but also
to regulate the salts within their shells. You may observe your
hermit crabs as they examine each shell with great care, picking
it up, turning it over, looking for any reason not to chose
it as their new mobile home. It is important that if there are
holes in the shell, especially in the whirl where the shell
water is kept, that you quickly find some suitable replacement
shells.
Differences in Seashell
Selection By Species
Aussie
Hermit Crabs and Ecuadorian/Pacific Crabs are very similar in
appearance and seashell selection. Thais or Rock/Purple shells
are found in Australia and Parts of the Pacific, as well as
other areas. They are available to Aussie Hermit Crabs and Ecuadorian
land hermit crabs and are often harvested from the wild wearing
the rather plain looking shells with an interior that is quite
smooth and pearly of nacre. There are many types of Thais shells,
and they are linked to Murex shells, which are another favourite
shell of many land hermit crabs. For information on other land hermit crabs view this video by Stacy of The Crab Street Journal
The Perfect Fit
It is important
to measure the cheliped of the hermit crab and match it up with
some shells that will offer a source of protection. If the hermit
crab can curl up within the shell, using the cheliped/grasping
claw as a little door such as in the image above, then they
will have a fighting chance against aggressive shell-fight bullies.
Keep Your Hermit
From Becoming Crabby - Avoiding Shell Fights
Often
if there is a dearth of suitable shells, hermit crabs will rap
against the shells of their tank mates, or attempt to drag them
out of the shell by the cheliped(claw) or peripods(walking legs).
As you can see, the barracade above would make it very hard
for the aggressor to pull this hermit crab from its prized Tapestry
Turban (Turbo petholatus) shell home.
You may find that
despite the presence of many suitable shells, there will be
some hermit crabs that just refuse to budge from their old and
battered natural or pre-worn shells. This can be quite frustrating
to owners who do try to provide new shells for them to change
into, however there are many reasons for this reluctance to
move on. Often, hermit crabs will prefer a pre-worn shell that
has been modified by many hermit crabs over the years and is
as snug as an old woolen jumper that while looks a bit daggy,
is quite cumfy and practical. They might prefer the weight or
opening type of the shell they are inhabiting to those offered,
so will wait until a more ideal shell comes along.
A Preference For
A Certain Type or Fit
I
have found that hermit crabs will often change into seashells
much like those they are in, if they like the particular 'fit'
for their abdomen. Just like we have preferences for the type
of shoes we wear, hermit crabs like a shell that fits 'just
right'. You might see hermit crabs whip their abdomens in and
out of shells while they make up their mind, OR wait around
until one of their tank mates moves out of a prized shell, and
then there is a seashell vacancy chain (domino effect) whereby
you may watch crab B slip into the discarded A, Crab C move
into the roomer discarded shell of crab B, and so on.
It is important
that if you have a hermit crab that desperately needs to change
their shells, that when you finally find a shell perfect for
their needs, that you keep the other hermit crabs from pinching
their shells. Perhaps just after a bath you could create a little
playpen out of a clean icecream tub and place some clean, suitable
shells with the hermit crab so that they have the opportunity
to change without having the misfortune of finding the shell
isn't such a good fit, but stuck in it because their 'old faithful'
shell was lost to them.
Seashell
Modification
"Hermit
crabs are a primary cause of wear to gastropod shells. Many
top-shells had crab-modifed apertures. Also, interior wear
patterns that corresponded to outer breakage areas were observed
in both crab-inhabited and abandoned top-shells. Vermeij (1987:243)
states that hermit crabs of the genus Coenobita actually resorb
the inner walls of the shells they inhabit, enlarging the
inner chamber. Desirable shells are used by many generations
of crabs, being outgrown, discarded, and reoccupied by other
crabs."1
If you have hermit
crabs such as Ecuadorians then perhaps you just need to offer seashells similar to those
they found in the wild, or those seashells proven to be a
hit, such as Thais hamastoma which is growing in popularity
and is also known as the Mexican Rock Shell."1
Think Like A Crab
Think
of how awful it would be if you found a pair of shoes on a beach
and went to try them on, but someone stole your shoes, and you
found that the shoes cramped your toes. You'd have to walk home
in shoes that were ill suited and wait until the next good shell
came along. If there were no spare shells available, you may
find that a desperate crab could take matters into their own
hands and simply fight to win ownership of the shell of another,
in order to survive. If you see shell fights, it is imperitive
that you re-assess your shell selections and isolate the aggressive
crab or it may lead to fatalities.
Say No To Painted Shells
A video by CNN on how land hermit crabs are forced into painted shells
Footnotes:1.
SCUDDER, S.J. AND QUITMYER, I.R(1998) Caribbean Journal of Science,
Vol. 34, No. 1-2, 41-49, 1998 Copyright 1998 College of Arts
and Sciences University of Puerto Rico, Mayag.ez Evaluation
of Evidence for Pre-Columbian Human Occupation at Great Cave,
Cayman Brac, Cayman Islands SYLVIA J. SCUDDER AND IRVY R. QUITMYER
Department of Anthropology, Florida Museum of Natural History,
University of Florida, Gainesville, Florida 32611
