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Whack! Jab! Crack! It's a Blackback Land Crab Smackdown | Deep Look

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Channel: Deep Look
Categories: Biology   |   Environmental   |   Science  
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It's an all-out brawl for prime beach real estate! These Caribbean crabs will tear each other limb from limb to get the best burrow. Luckily, they molt and regrow lost legs in a matter of weeks, and live to fight another day.

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DEEP LOOK is a ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.

On the sand-dune beaches where they live, male blackback land crabs do constant battle over territory. The stakes are high: If one of these baby-faced crabs secures a winning spot, he can invite a mate into his den, six or seven feet beneath the surface.

With all this roughhousing, more than feelings get hurt. The male crabs inevitably lose limbs and damage their shells in constant dust-ups. Luckily, like many other arthropods, a group that includes insects and spiders, these crabs can release a leg or claw voluntarily if threatened. It’s not unusual to see animals in the field missing two or three walking legs.

The limbs regrow at the next molt, which is typically once a year for an adult. When a molt cycle begins, tiny limb buds form where a leg or a claw has been lost. Over the next six to eight weeks, the buds enlarge while the crab reabsorbs calcium from its old shell and secretes a new, paper-thin one underneath.

In the last hour of the cycle, the crab gulps air to create enough internal pressure to pop open the top of its shell, called the carapace. As the crab pushes it way out, the same internal pressure helps uncoil the new legs. The replacement shell thickens and hardens, and the crab eats the old shell.

--- Are blackback land crabs edible?

Yes, but they’re not as popular as the major food species like Dungeness and King crab.

--- Where do blackback land crabs live?

They live throughout the Caribbean islands.

--- Does it hurt when they lose legs?

Hard to say, but they do have an internal mechanism for releasing limbs cleanly that prevents loss of blood.

---+ Read the entire article on KQED Science:

---+ For more information:

The Crab Lab at Colorado State University:

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