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Home: Caresheets
 Behaviour
in the Wild
Land hermit crabs are territorial animals, and as such
they will often act aggressively towards one another to
establish a 'pecking' order among their colony. Sometimes
this can be in the form of 'feeler' or antennae fights,
others in violent pushing or flicking fellow tank mates
out of the way. Usually this is not serious enough to warrant
intervention. However, some hermit crabs will act in a manner
that is harmful to other hermit crabs, often trying to pull
their hermie buddy out of a desired shell, or attacking
eyes, antennae, claws, legs or abdomen.
If you witness behaviour that may be harmful to one or
more hermit crabs, it is important to separate them until
the aggressor has setled down. Sometimes tank aggression
can be a precursor to a moult, or the result of being picked
on or bullied in the past. The most common form of aggression
is where one crab tries to pull their tank-mate out of the
security of the seashell.
Handling with Respect and Gentleness
It shouldn't be forgotten that hermit crabs are not toys,
but living animals. It is important to pick them up gently,
carefully and talking softly to them to let them know that
they are safe is often a good idea. Use slow and gentle
movements and always remember to carry them steadily. If
you were placed on a palm and thought you were going to
tumble off the edge, what would you do? A hermit crab doesn't
have hands with fingers, it has claws and legs. In order
to save itself it will grip on with what it has available,
so remember to help your buddy know he is safe from harm
and put yourself in the place of the hermit crab at all
times. A hermit crab treated with respect and gentlness
will be gentle. A hermit crab that is handled roughly and
with anger or haste will soon let you know that he can be
just as crabby!
Autotomy
In the wild a hermit crab will "throw" a claw
or leg if another hermit crab tries to pull them out of
their shell. This is a responsive behaviour and their limbs
are built in a way that they are able to "drop"
or "throw" a limb easily so they may survive an
attack. This is called Autotomy.
You may see your hermit crabs climb over the top of each
other, or perhaps flick each other out of a prized spot
or corner. This is natural behaviour, and doesn't normally
harm your hermit crabs. You may have watched puppies or
kittens playing and vying for the best spot near Mummy dog,
'rough-housing' and play fighting. The flicking and tumbling
another hermit crab out of the way is just in the nature
of the territorial hermit crab and helps to establish 'pecking
order' amongst hermit crabs.
Stridulation (Chirping or croaking)
I was doing some reading of my "Biology of the Land
Crabs' book today and came across a chapter on stridulation
behaviour in land crabs. Of specific interest was a paragraph
on Coenobita:
"Stridulation in conjunction with posturing is common
in aggressive displays of Coenobita (Hazlett, 1966; S. Gilchrist,
unpub). Clicking by rapping of appendages together and by
tapping the shell are integral parts of aggressive encounters
of C. clypeatus and C. compressus. When alarmed, Birgus
latro briskly stamps the second peripods. At other times,
even when not apparently alarmed, this crab produces continuous
clicks (Grubb, 1971). This may be a proximity warning to
con-specifics."
Dunham, D. W., and S. L. Gilchrist. 1988. Behavior. Pp. 97-138 in Biology of the Land Crabs, W. W. Burggren and B. R. McMahon, eds. Cambridge: Cambridge University Press.
I have other refrences which I will dig up (literally,
its all in storage) and share. From personal experience
my hermit crabs mainly chirp when there is another crab
bullying them. Prime example was when I heard 'rheet rheet
rheet' and went over to the tank, saw one crab over the
top of another one and trying to pull the poor crab out
of its shell! I'd be making a lot of noise too! Some crabs
have chirped or croaked when being picked up, but very rarely.
It reminds me of a car alarm - sometimes its a false alarm,
other times it means something is wrong.
Antennae
Fencing
Another thing that hermit crabs like to do is to go up
to each other and have a hermie 'antennae/feeler wiggling
and touching' encounter.
You might see the antennae moving
quickly, and brusihng against the antennae of the other
hermit crab.
This may take a few minutes to die down, and
either crab lose interest. Sometimes it is almost as if
they are talking in code, giving signals to each other.
As long as they are not hurting each other, it is often
best to let them interact and develop their social skills
with other land hermit crabs.
Sometimes they may even brush cheliped, grasping claw,
against each other. IF this progresses into an entirely
aggressive act, such as trying to sever antennae, limbs,
eye stalks or removing the other hermit crab from its shell,
THEN it is time to 'break it up'.
Example Shell Swap Behaviour:
 When
one crab likes another's shell, say Crab A likes Crab B's
shell, Crab A will go up to Crab B's shell, knock its shell
( that of Crab A) against the other crab's shell (Crab B),
causing the crab in the desired shell (Crab B) to come out
and have a look at what is going on. Now the first crab will
try to pull the second crab out of its shell by a cheliped
or other limb. The second crab will normally drop his cheliped(grasping
claw) or leg/s and retreat inside his shell, using his remaining
cheliped to protect himself. Preferring to loose a limb instead
of loosing a shell.
If there is a shell involved, it often helps if you place
the attacker into a container with a number of suitable shells
in different sizes, shapes and weights. It could well be that
your hermit is crabby because his shell is too small. Imagine
if you had to wear shoes two sizes small or large for you,
and you were stuck in a glass tank and not able to go shopping
to find a new one. What else could you do, but fight for the
best shells with your tank mate. Remove the source of the
aggression, and you will have relative peace and happiness
in your crabarium.
If you don't remove the cause of the stress, you may just
find that your overly stressed and crabby companion has ripped
another hermit crab out of its shell, or viciously attacked
it. If this happens, it is time to re-evaluate your crabitat
and seashell collection, but first isolate the aggressive
hermit crab and give it somewhere comfortable, equipped and
containing an area it can retreat within darkness.
Somewhere Dark and Private
 It
is important that you have several spots within your tank
for your hermit crabs to retreat within to escape the stress
of life in captivity, mostly in partial darkness or protection
from other hermit crabs. The most popular forms of tank decorations
that meet this need are the Rock Caves,
Coconut Huts,
Hideout Dens, Terracotta (clean) flower pots, and more. Just
like reptiles and many other animals, hermit crabs will be
significantly less stressed if they believe they are protected
from predators and allowed some cover of darkness.
Some Strategies
Over the past seven years I have had a handful of hermit
crabs that were dangerously aggressive to their tank mates,
and each time the best remedy was:
1. isolation
2. dark and private, quiet
3. access to more seashells
4. slowly building up a sense of trust with the hermit crab,
through talking and treats
5. observing the hermit crab with others at bath time or on
supervised visits to the crabarium
6. if there is still a problem, re-organising the crabarium
and allowing all the hermit crabs to play outside of the crabitat
for a while in neutral territory (such as the weekly buffet
container).
7. rotate the seashells within the tank, so that the hermit
crabs think they are getting new shells, so they will check
each out -- which may spark a vacancy chain massive seashell
swap.
Larger Crabitats = More Space + Less Stress
 If
you are still having problems then it may help if you separate
the crabs into two tanks, or upsize to a larger tank if needed,
with a barrier. Most of the time people use a 10Gallon or
20Gallon LONG tank, which has very limited surface area. If
you buy a larger tank, perhaps get one custom made. It is
often cheaper due to the thinner base -- no need to have the
thickness due to heaviness of water in fish tanks. If you
can't afford this, it might help if you exercise your hermit
crabs in a large, clean storage tub or other plastic container
for a few hours a day (weather permitting).
Hopefully this primer on aggression has been
of use to you. Why not tell a friend
about this website?
References:
Dunham, D. W., and S. L. Gilchrist. 1988. Behavior. Pp. 97-138 in Biology of the Land Crabs, W. W. Burggren and B. R. McMahon, eds. Cambridge: Cambridge University Press.
Image References:
Photos of Coenobita perlatus by Crazy Sean <trashyhonky>
Photos of Coenobita variabilis by Vanessa Pike-Russell
Animation of shell change by Matthew Turnbull and Vanessa Pike-Russell
Behaviour: Aggression | Chirping | Inactivity | Moulting
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