StarRider nailed it. Cichlids sleep at night usually resting at the bottom. Lobsters, shrimp, crawfish etc will grab your smaller cichlids at night. They scavenge the entire tank top to bottom, up and down plants, decorations, wood or whatever else you have in your tank.
I just used a spare 10g to house a cray. No heater, no filter (at the moment) and some feeder guppies. He's a cute little bugger but dosen't do much when the lights are one. Considering I haven't spent a penny on it, it's kind of neat.