Don't know about your green legged dude, maybe post a pic. I have about six smaller hermits, combo of blue legged & red legged. They're all good, great little clean up crew. A couple of years ago though I purchased a White Spotted hermit since he looked so cool. Was relatively small when purchased, but didn't take long & this guy got large & destructive. The odd time he'd try to snag one of the little guys out of their shell, but never succeeded. In the end though, he just got too big & I took him back to the LFS where I got him. Before that, he devoured a sand sifting starfish and two pencil urchins. It's entirely possible these critters were doing poorly & he simply finished them off, but he was also just knocking stuff over due to his sheer size. One thing though, when he wasn't doing the bull in china shop routine & eating tank mates, he was one of the best sand sifting critters I've ever had in the tank. Would be a great addition to a sump with a sand bed, but I don't have one of those.
Here's a photo of the dude, with a blue legged hermit hitching a ride on his shell (gives a good perspective of relative size!) & one of the pencil urchins he finished off in the background. And yes, there's a bit of a hair algae issue as well.
