The Visitors are split in separate caste's, each with a defined purpose.
The Queen is the leader of her species. She is responsible for providing bliss to her subjects and to birth offspring (Soldiers+1 Queen egg) in times of need.
V soldiers are Visitors born from the Queen. They have only one purpose: to fight. They have the ability to cause mass destruction and not even an axe, buried deep into them can stop them.
V Trackers are assigned to smell out scents and to find people whom they are told to find. There sense of smell is extremely powerful and able to follow on that scent. They never engage in combat and merely lurk in the shadows and find their target and report back to their Queen.
V Workers have a more wide range of choice, for they can be a scientist, guard, doctor, etc.