I've had a few assassins in several tanks for a year or so. I rarely ever see them at all, and have never actually seen one predating on another snail. They have grown much larger, and the number of bladder and ramshorn snails in those tanks is a fraction of what it once was, so the assassins are definitely doing their job, but they are being very discreet about it. If you are expecting action, drama, or instant results...you may be disappointed.