Hostage situation . . . may be be an emergency (?)

Question
I've had my 3 hermit crabs for 2 years and they've all gotten along really well for the most part, all three slightly different sizes (enough that shells haven't been an issue). I am unaware of their genders. Over the past few days, I've noticed the biggest (Marco) start to bully the mid-size one (Butler), but it was easily detered by separating them to separate parts of the aquarium. About 24 hours ago, it was time for cage-cleaning, so I picked up one of the cocohuts to find Butler fully in his shell, opening up, while Marco holding on to the shell, refusing to let go. Marco doesn't seem intent on tearing Butler from his shell because I caught Bulter half out of his shell several times with no aggressive behavior between them (they were somehow startled during one of these times (I wasn't moving, so I'm not quite sure how) and Butler retreated into his shell and must have instictively pinched the air, but caught the end of Marco's leg. A little bit of chirping and about 10 minutes later, Butler let go). This seemed to be the only 'painful' experience between the two. The smallest one, Evans, has been hanging close to the conflict since he learned of it, and at times, it seems as if he is trying to get them to stop. Worried about water for Butler, I gave him a few spurts and he seemed to appreciate it (came further out of his shell and was drinking the water). Every so often, Marco will turn/move Butler and his shell, but still refuses to let go. Butler's shell used to be Marco's about 6 or 7 months ago, but Marco is obviously too big for the shell. From what I've noticed previously, Marco seems to be the 'head crab' of the three. It was my hope to catch them apart and separate them, but the opportunity hasn't shown itself. The humidity and temperature of their habitat has not changed durastically, so that doesn't appear to be an issue.

Answer
You really need to find a way to get them separated. A crab intent on shell stealing can do the crab inside real damage. I would isolate the aggressor and remove and clean all the shells. You may have to special order some for the aggressor that are perfectly sized. I had a similar experience that I wrote about on my website.

http://naturallycrabby.com/home/blog1.php/2008/07/21/shell-fighting-in-hermit-cr...