Some hitchhikers are harmless, others can be fish killers. I had nabbed a hitchhiker shortly after I set up my 55, some 4 years ago. Trapped him in a glass and sumped him. A couple of years later, after not having added a thing for about 2 years, my Coral Beauty began to suffer tail damage from unknown sources... he was king of the tank. One day while observing the tank, I noticed a crab, front and center in the rocks. Would not have noticed him if he hadn't moved. Set the drinking glass crab trap that night, caught not one, but TWO crabs!
Sumped them both, and no more fin/tail damage to Coral Beauty! Eventually one crab ate the other!
Some hitchhikers are relatively harmless, especially when tiny, but as they grow and scavenge, sooner or later they get hungrier and can take down a fish as it sleeps.
I've had people observe that their long-time tank inhabitants do fine, but any newcomer vanishes without a trace... I surmise that the long-timers know of the crab and where it lives and avoid it, but the newcomers don't know, pick the wrong hidey hole at night and get taken out without a trace.
Crabs are relatively easy to catch with some smelly bait (fish food) in a drinking glass with the lip against the rock (particularly where you think the crab may be). On the other hand,
mantis shrimp are another story - they can swim out of the drinking glass trap - a soda bottle with the top funnel inverted usually works best - bait the bottle with something smelly, cut off the top/funnel and invert it - the mantis will find its way inside the bottle to collect the bait, but has less chance of finding its way out again.
Jenn
I just made that up all by myself!! Anyways, it's late and I'm getting a delerious... HTH
