Nasty nighttime surprise

[0sprey]

I crept up on my tank with a flashlight last night; I was watching all the different pods scurrying around (quite entertaining, try it sometime if you haven't already), and I started to shine the flashlight into all the little hidey-holes in the rock. Then I saw something move in the cracks, slowly sheltering itself from the light...
Something big.
And spiderlike.
I have at least two enormous crabs in my tank. Possibly more. Their carapaces alone are at least 2 inches wide, definite fish-killer size. They have all the supposed earmarks of 'dangerous' crabs, too... hairy carapace, dark pincers. I'm stunned that I've had all the rock in my tank for at least ten months (no coral additions since four months ago), and yet these things have escaped my notice. I scrubbed down all my rock too, very carefully, and never saw any crabs.


I've heard of tipping a baited beer glass to catch them, but I don't have a DSB, so I'm not sure I'll catch much more than my hermits and bristleworms. Should I try to bait them out? They don't seem to move very fast, but I remember thinking that about my brittle star before I scared him for the first time... Any other suggestions?