Home Shell of the Naked Hermit Crabs: Fiddlers: macho crabs of the shore

The Big Useless Claw Story
Messages: "every inch of the shore is alive, every step kills, stick to the death zone"

For a shore walk (you can go straight to Step 3 if you're on a boardwalk)
Step 1: "Stay very still and you will see some interesting animals on the sand. They are very small and very sensitive to your footsteps. If you wave your arms around they will think you are a bird and will hide. Pretend you are a tree and they will come out."

This will make visitors get used to not stomping around. To be still and look carefully for small things that will only come out when there is no disturbance.

Step 2: If it's taking a while for the crabs to come out "While we wait, let's look around us and I'll tell you about some of the special ecosystems we can see on Semakau. Meanwhile DON'T MOVE!"

Step 3: Once crabs are active, "How many claws does the crab have?" Eventually someone will say "One".

Step 4: "Actually it has two claws. The big claw is so big that it misses the mouth. It has a much tinier claw that it uses to feed itself. Can you see one feeding?"

Step 5: "Only the male crabs have one big useless claw. The females have two small claws so they can feed twice as fast."

Step 6: "Why do you think the males have one big useless claw?" Usual guesses: to find food, for fighting, for defence from predators. Explain briefly and clearly why these are not the case. Goad them with "Why do all boys have big useless things? Like sports cars?" Eventually someone, usually a girl or a small child, will say "To attract girls"

If the visitors have been very very still, you can say "These tiny crabs are all over the place. You can see some near your feet too! See!!! Every inch of the shore is alive with creatures. Some of them are small and buried in the sand. Every step we take on the shore will most definitely squash something."

For shore walk
"We have designated a trail on the shore. It is a death zone. Just like any nature park in Singapore. At Sungei Buloh or Bukit Timah, we don't walk anywhere we want to but have to stick to a trail. Otherwise, a larger and larger area will become 'botak' as footsteps kill off small plants and animals.

"To minimise this death zone, please stay close to me and try to stay in a single file."

If you are not the first group "Follow the trail made by the group in front. Then you don't kill things that they haven't already killed."

For boardwalk
"It's great to have a boardwalk, so we can have a look at these animals without killing them!"

Tips on dealing with fiddlers

Please do NOT pick up fiddlers. Visitors will do as we do and not as we say. In any case, if we catch them and put them down far away from their burrow, they will be stressed and may not be able to find protection and then die.

Please do NOT dig up fiddlers either. This is destructive to the habitat, and encourages visitors to dig up everything they want to see. Instead, encourage them to be patient and wait for animals to come out and go about their normal business.

Naked Facts:

The male waves his large pincer in a style and rhythm unique to his species in order to attract the ladies. Fiddler crabs got their name for this behaviour, which resembles a musician playing on his fiddle. Interactive activity: You can do the fiddler movement using one of your arms to demonstrate to visitors how fiddler crabs fiddle.

The eyes of a fiddler crab are mounted on long stalk giving it a good all-round view of the air and the horizon. This is for potential mate, rival and early predator detection. When the crab scuttles back into its burrow, the eyestalks fold down into grooves along the body.

Interactive activity: Use two fingers from each hand to illustrate this point.

The larger claw can be its either right or left claw. If an adult male loses its fiddler claw, the remaining claw grows to the same size as the lost claw, the claw it regenerates becomes the smaller claw.

Sex sells: When a male Fiddler crab succeeds in persuading a female to mate with him, they retire into his burrow. The female may remain there until the eggs hatch. The eggs hatch into free-swimming larvae that drift with the plankton, changing into yet another form before settling down and developing into fiddler crabs.

Too Much Information

Fiddler crab species are distinguished by the structure of the male's enlarged pincer. They are not reliably distinguished by the colour of bodies, pincers. The species of females is hard to distinguish.

Fiddler crabs cannot swim and prefer to breathe air. So at high tide, they hide in their burrows, plugging the entrance with a ball of sand to trap some air inside. However, they need water to keep their gill chambers wet as well as to process their food. They absorb water from the wet sand through hairs on their legs.

Porcelain fiddler crab (Uca annulipes)

Distinguishing features of the enlarged pincer of the male

outer side is smooth and does not have a triangular depression (most observable difference)
the movable upper finger extends past the immobile lower finger.
has a ridge of bumps on inside or the 'palm' of the pincer.