Sunday, March 25, 2012

It Will Cost You Your Arm

You hear of animals losing their limbs when being attacked by predators all the time. Lizards lose their tails, lobsters and octopuses losing legs... But nothing is more bizarre than an animal willingly removing an appendage after being attacked.
 The above video shows female boobys defending their nests from thieving crabs. The crabs take quite the hit from the birds and end up damaging their claws. Initially, I thought that maybe the damaged claws might be nurtured and eventually usable as before.  To my surprise, the crab simple popped off it's own arm; ripped right out of the socket.  The reasoning behind this is quite simple. Crabs go through a process called molting which regenerates the carapace that protects the crab's body as well as its other appendages. So, with each molt a new portion of the crab's appendage would be restored and eventually fully restored and fully functional.

The regrowth of an appendage begins with a bud in the place of the old appendage. This is evidence that the crab removed the appendage on its own accord. However, there are some creatures that suffer the removal of their appendages not by their choice and so the regrowth process is much different.
Sometimes, individual crabs have to regenerate both of their claws. In this case, the crabs become more of scavengers rather than predators. This would make defending themselves incredibly difficult but the regeneration process is not incredibly long (around a year) and in due time the crabs would have their appendages back and ability to defend themselves. Good things this is a quick process because it may have hosted an arm AND a leg.


  1. I have seen my hermit crabs do something like this when they lose their claws, but I do not think they pop theirs off on purpose. I was going to ask how long they took to grow back but about a year answered that question. But, when the crabs do this, if it is usually their claw that protects them, for a year how do they protect themselves? And does that affect their way of life for a while due to not having the claw that protects them and for some males attracts females?

  2. They use their other claw (the smaller one) to protect themselves from predators but during this time they are not as active as before, allowing them to stay out of reach of predators. It does effect their way of life depending upon the sex. Most males only feed with their small claw and so if the large claw popped of then they would still be able to feed. If this happened to a female crab her feeding would be limited because they use both hands to feed.