A crab that can break coconuts, grows as big as a dog, steals anything that isn’t nailed down, and enjoys a tickle. Crab expert Rick Webber introduces us to the largest land-living arthropod in the world.
The wall above the television in Planet Pasifika is home to a specimen that often goes unnoticed, but it’s rather special.
It’s a species of crab that mainly eats coconuts and other tropical fruits, but is also known to scavenge dead and decaying animals and even eat live birds – a coconut crab.
It’s also notorious for stealing all sorts of camping equipment and anything else that it can move.
The largest land-living arthropod
The crab we have on display came from American Samoa and as our crab expert Rick Webber puts it, “it’s a tiddler compared to how large they can grow” – but is still worth a look!
They can grow up to a metre leg span, reach over 4 kg in weight, and can live for up to 60 years.
Coconut crab claws are so strong that they could easily snap your finger in two. However, they do have a ‘softer side’. Rick shares these wise words, “If you’re unlucky enough to have your finger clamped by a coconut crab it won’t tend to let go. Don’t scream and shout, just grab a stick and tickle it on its soft underside and it should succumb.”
The palm thief
Coconut crabs, also known as robber crabs or palm thieves, are a species of hermit crab that are found mostly on tropical islands from Zanzibar, across the Indian and West Pacific Oceans, to the Central Pacific, including Fiji and Samoa.
Within this area, their distribution mirrors that of coconut palms. Rick says “We know they climb trees, but we’re not completely sure why. They might be picking coconuts, but this is a matter of debate because no-one seems to have proved that they’ve seen them nipping coconuts off.”
“However we know they eat coconuts when they’re on the ground. They use their amazing strength to target the weak point of the coconut (where the three eyes are) and prize it apart”.
The life of a coconut crab
Coconut crabs live on land but to complete their life cycle female crabs must be able to visit the sea.
After laying, the eggs are attached beneath the mother’s abdomen. At hatching time she wades into shallow sea water and hatches tiny sea-going larvae in the water. She must be careful not to go beyond her depth as she’ll drown.
The mother then eats the empty egg shells. As Rick explains “this is good recycling as the calcium carbonate from the egg shells helps harden their own external skeletons, and is not wasted.”
The larvae spend 3–4 weeks eating and growing in the sea, before changing into little, hermit crab-like, animals that can still swim.
Like most hermit crabs, these come ashore and find a seashell to live in. As they grow, their ‘tail’ develops hard external plates for protection from enemies, and against moisture loss. They can then abandon their seashell home.
Coconut crabs also dig burrows to protect themselves against heat and enemies. They are not an endangered species but, due to people pressure, on many islands their numbers have become greatly reduced, or they have disappeared altogether. They’re also a delicacy in some island states where collecting rules or bans are sometimes used to ensure their survival.
There’s still nature to be seen
Our main nature exhibitions may be closed for now but we still have more than enough weird and wonderful creatures on display to keep you entertained.