Sometimes they dig, sometimes they don't. Hard to tell why. I suspect that some of the time it's a spawning or pre-spawining behavior. Could be boredom. They get interested in different things. For awhile it's digging, then maybe playing in the bubbles, watching TV, checking out the people in the room, terrorizing their tankmates, rearranging the plants (maybe secretly studying Feng Shui -- sometimes their choices are better than mine). Mine don't really hide in the caves, though they will check them out thouroughly -- even if they're too low for them they'll turn on their side so they can get in and inspect. Be careful how you build them -- they're swimming bulldozers. Any time I re-arrange or add anything all the cichlids (2 O's, 2 Severums, and a Juripari) have to come check it out from every possible angle.