What will cause a crab to die?

[Ariel110G]

What will cause a crab to die? I just lost my biggest crab today, (I got a call from my wife) I know that it can be molting but if it?s not & he did die what can cause a crab to die. I know for sure that it?s not a food problem, I?m the type that can over feed some times, & there is a lot of algae for all my crabs to take care off. So what can it be?

 

[skene]

old age.