pest crab

[Snappy]

I have a crab that has been eating my zoos. He has devoured this colony

and as well has carted off 3 seperate frag plugs of zoos into his den. He is too big for a bottle trap and very smart, I have caught him twice but it shook loose so now he has no front claws as that is all I was able to hang on to.
Any ideas? He is too smart to skewer, he seems to have a path system through the rockwork so he very seldom exposes himself. I need to get that rotten bugger. He is costing me a fortune in zoos, hermits & snails.