Crabs Trade Shells in the Strangest Way | BBC Earth
Summary
TLDRHermit crabs constantly search for new, larger seashells to inhabit as they grow, gathering in groups when a suitable empty shell washes ashore. They cooperate surprisingly by lining up from largest to smallest crab and orderly exchanging shells to each get a properly fitting new home. The crabs patiently wait for just the right additions to the chain in order to trigger the intricate housing swap in an amazing display of collective organization and intelligence just to survive.
Takeaways
- 😱 Hermit crabs use empty seashells as mobile homes, needing to upgrade to a bigger shell as they grow.
- 😅 When a new shell washes ashore, crabs gather to try to upgrade, arranging themselves by size.
- 👉 The crabs line up to exchange shells, each moving into the shell vacated by the crab ahead.
- 😊 The chain reaction allows each crab to move into a fitting shell, triggered when the biggest crab moves.
- 🤔 None of the crabs can make a move until the chain is fully formed with the right sized crabs.
- 😮 A small crab finally takes its place to complete the chain, allowing the shell swapping to start.
- ⚠️ A crab left without a shell risks death by cooking under the intense sun.
- 😥 Despite the shell swapping, one crab ends up with just as small a home as before.
- 😫 The final shell even has a hole, but is still better protection than no shell.
- 🕵️♂️ The crabs demonstrate remarkable cooperation and order to ensure as many as possible get better shells.
Q & A
Why do hermit crabs need to find new seashells periodically?
-As a hermit crab grows over time, its shell becomes tighter, so eventually the crab needs to move into a bigger shell to have enough room.
Why is it difficult for a hermit crab to find a suitable new shell?
-Suitable empty seashells are scarce, so when a new shell washes ashore, many crabs will gather to try to claim it, even if it is too big for them.
How do the gathered crabs decide who gets a new shell that washes ashore?
-The crabs arrange themselves into an orderly queue from biggest to smallest. This allows them to exchange shells in an organized way so each crab gets a appropriately sized shell.
Why can't the crabs exchange shells as soon as they line up?
-None of the crabs can move into a new shell until the chain of crabs is complete, so they wait for the right sized crab to arrive and take its place in the queue.
What happens when a crab finally moves into a new shell?
-This triggers a chain reaction where each crab hurries to move into the shell vacated by the crab ahead of it in the line, allowing for an orderly exchange.
What happens if a crab ends up without a shell after the swapping?
-Being exposed without a shell is fatal for a crab due to the intense tropical sun. So even a damaged shell is better than no shell at all.
Why don't the smaller crabs wait for a shell that properly fits them?
-The smaller crabs settle for a shell that is too big because suitable shells are so rare. Having a shell that is too big is better than the risk of being left with no shell.
What social behavior do the crabs display in this situation?
-The crabs display cooperative, organized behavior by lining up according to size and waiting their turn to exchange shells in an orderly fashion that benefits the whole group.
How does this scene illustrate the challenges hermit crabs face in their environment?
-It shows that finding adequate shelter is an ongoing struggle, as they periodically outgrow their shells. Waiting for scarce resources forces social coordination.
What might happen if a crab refuses to participate in the shell exchange queue?
-If a crab does not join the queue, it likely won't get access to any of the shells. And if it tries to take a shell out of turn, the other crabs could prevent it since they outnumber solitary crabs.
Outlines
🦀 Hermit Crabs Line Up to Exchange Shells
This paragraph describes how hermit crabs outgrow their shells over time and must find new, larger shells to live in. When a suitably large empty shell washes ashore, a group of smaller crabs that need bigger shells waits for other crabs to arrive and arrange themselves into a size order queue. They then systematically exchange shells from largest to smallest crab until each has a better fitting shell.
Mindmap
Keywords
💡Hermit crab
💡Mobile home
💡Shell exchange
💡Chain reaction
💡Death sentence
💡Cooperative behavior
💡Size hierarchy
💡Opportunism
💡Zero-sum game
💡Upgrade vs downgrade
Highlights
Hermit crabs use abandoned seashells as mobile homes
As a crab grows, its shell becomes an ever tighter fit, so eventually it needs to move to a bigger one
Suitable empty shells are scarce, so crabs gather when a new shell washes ashore
The crabs line up by size to exchange shells, with the biggest at the front and smallest at the back
The crabs wait for the right sized crab to come and complete the chain so they can swap shells
The latest arrival crab pushes to the front to start the shell swapping chain reaction
Each crab hurries to move into the shell vacated by the one ahead of it in line
A new arrival muscles in at the end, leaving the smallest crab without a shell
Being left without a shell is fatal since naked crabs cook quickly under the hot sun
After all the swapping, there is still one unused shell left, but it has a hole
Even a damaged shell is better protection than being homeless for a hermit crab
Crab grows over time so needs to move into ever larger shells
Crabs lack their own protective shells so rely on finding empty ones
Crabs have an orderly system to fairly exchange shells according to size needs
Strongest crab starts the chain reaction of sequential shell swapping
Transcripts
Hermit crabs use abandoned seashells as mobile homes.
As a crab grows, its shell becomes an ever tighter fit.
So, eventually, a crab needs to move in to a bigger one.
Suitable empty shells are few and far between...
And this one is far too spacious for this crab.
But instead of continuing its search, this small crab settles down to wait.
Other crabs, also looking to upgrade to a bigger home,
soon gather whenever a shell washes ashore.
Unfortunately, the new shell is too big for them, too.
Despite that, the gathering crabs begin to measure each other up,
and then they do something really rather extraordinary.
They arrange themselves into an orderly queue.
The biggest at the front, smallest at the back.
They're lining up with one aim, to exchange properties.
But none of the crabs can make a move, because the chain is not yet complete.
They're all waiting for the right sized crab to come along.
And this is it.
The latest arrival pushes to the head of the queue.
At first, the chain falls apart.
As it reforms, the small crab finally makes its move...
and takes its place at the end of the line.
After a close inspection,
the big crab moves in.
This triggers a chain-reaction.
Each crab hurriedly moves into the shell
vacated by the crab ahead of it in the line.
Just as the small crab attempts to move into its new home...
a fresh arrival muscles in.
To be left without a shell is a death sentence.
A naked crab will quickly cook under the intense tropical sun.
But, after all the swapping, there is still one shell left.
Sadly, it's no bigger than this small crab's original shell.
And worse, it's got a hole in it.
But even a bad shell is better than being homeless.
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