Wednesday, May 2, 2007

Hermit crabs and their friends

Three NAKED Facts

NF#1: A hermit crab without a snail shell is a naked hermit crab!

Thoughtful question: How is the hermit crab different from the crabs you eat?

The crab you eat has its backside folded under its body and is protected by a hard shell.

A hermit crab looks like a cross between a crab (the front end of the hermit has hard claws and legs) and a shrimp (its backside is long and fleshy). The hermit crab's backside is soft and is not protected by a hard shell. (You can use the Naked Hermit Crab logo to show how the hermit crab looks without the shell. The diagram on the left is also in the Chek Jawa Guidebook.)

A hermit crab tucks its soft backside into an empty snail shell for protection. A naked hermit crab will soon be a dead hermit crab.

Please don't take any shells home with you. Hermit crabs need them more than you do!

NF#2: Don't pull the hermit crab out of its shell!

The hermit crab has little claws on its backside to cling onto the shell. If you try to pull the hermit crab out of its shell, it will cling desperately to the shell with these claws. So you may rip the hermit crab into two!

NF#3: Hermit crabs have many friends

Corny jokes: A hermit crab shell can get very crowded. If you were a hermit crab, you'll never be lonely!

The hermit crab makes such a comfortable home that other animals settle into the same shell. These include slipper snails, tiny porcelain crabs and small sea anemones.

Interactive activity: Let's try to find some of these friends on this hermit crab shell...

Thoughtful question: Why do you think living in the hermit crab's shell is so comfy?

The hermit crab creates a constant current of water. Friends get free air-conditioning.

The hermit crab is usually a messy eater. Friends get lots of free left-overs without having to look for food.

The hermit crab also moves around to find food, as well as to hide from danger. Friends enjoy all these by sticking with the hermit crab.

Corny joke: Living with a hermit crab is like living with your parents...

Another issue to explore...

Should we keep a hermit crab as a pet? Some reasons why we should not

Hermit crab friends that live on their shells need hermit crabs. If we remove the hermit crab, their friends will not have a place to live.

How much time will you spend with your hermit crab pet at home? 15 minutes, half an hour? Will you do this over many weeks, months? Or will you soon get bored and ignore your hermit crab pet?

Why not just spend that 15 minutes on the shore with a hermit crab? Here, the hermit crab is happy, doing its own thing, being with its friends. After you've spent time with it, leave the hermit crab behind in its natural home, while you go back to yours. You can always come back again to visit the hermit crabs on the sea shore.

Some tips on handling hermit crabs

To get the hermit crab to come out, you can try breathing on it, not blowing, just exhale (not sure why this works...perhaps it only works with MY bad breath :-). The surest way is to pour SOME (not the whole bottle of) freshwater into the shell.

Hermit crabs, especially big ones, can give a nasty pinch. Be careful.

Try to show tiny hermit crabs as well as big ones. To drive home the message that ALL shells should stay on the shore.

Too Much Information
Yes, the info is fascinating (especially to Naked Hermit Crabs). But if you tell them ALL to the visitors in one go they might faint from hermit overdose. Best to only share this if the visitors ask.

Does the hermit crab kill the snail to get its shell?
Hermit crabs never kill the original occupant of the shell. They may, however, quarrel with each other over a desirable shell. The hermit crab in this photo is patiently waiting for the small whelks to clean out the recently demised original occupant of the shell before trying on the empty shell.

What does a hermit crab eat?
Some hermit crabs are scavengers, i.e., they eat dead animals. These have a keen sense of smell to find their food. Others eat seaweed and muck (detritus).

Does the hermit crab always use the same kind of shell?
No. The same kind of hermit crab can use different kinds of shells. Even a tiny broken shell or an ugly shell covered with barnacles is a potential hermit crab home.

What happens when a hermit crab gets too big for its shell?
As a hermit crab grows bigger, it has to find a bigger shell. If the shell is too small, the hermit crab can't hide properly inside the shell from predators.

Corny joke: Hermit crabs understood the concept of 'upgrading' long before other Singaporeans!

Hermit crab musical shells: Before switching shells, a hermit crab will tentatively test out the new shell first, while holding on to the old one. If the new one is not ideal, it instantly goes back into the old shell. Often a whole group of hermit crabs will gather around a new empty shell. If the new shell is taken by a hermit crab, another hermit crab may take over the recently abandoned shell. And so on with the rest of the hermit crabs like musical chairs but with shells!

Are there any hermit crabs that can live without an empty snail shell?
The largest hermit crab in the world is the Robber or Coconut crab (Birgus latro). This hermit 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.

What are the different kinds of hermit crabs on Singapore's shores?

The Striped-hermit crab (Clibanarius sp.) has stripes along its legs. It is usually orange, but sometimes, blue or even dark green ones may be seen. Its pincers are of equal size. It is more commonly seen on our Northern shores.
The Tidal hermit crab (Diogenes sp.) is drab and has one pincer that is much bigger than the other.
The Land hermit crab (Coenobita cavipes) has squarish legs and pincers and is usually a shade of violet. It is usually found only on undisturbed shores, near the high water mark and is more active at night or near sunset or sunrise.
Tiny hermits Piles of tiny shells of different kinds are often encountered on a stone at low tide. These are usually homes to tiny hairy hermit crabs. Almost all our shores have these hermit crabs.
Hermits with no name I have yet to find out the identity of these two different kinds of small hermit crabs. They are commonly seen on good reefs and coral rubble. I have seen both on Sentosa.

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