Healers are a vital addition to Blood society because they are the ones who heal the physical bodies. Unlike Black Widows who are healers of the mind, Healers are instinctually drawn to the art of healing the body. They have an inborn knowledge of the methods and theories they should be using, but additional training is required for society to consider them "fully trained" and thus fully trusted to act with the authority of medicine on their side.
Healers are often thought to be much like Queens, especially in their single minded tendency to think their own life is less important than all those around them. Because of this, Protocol demands that any unmarried Healer is required to have an escort to accompany her, so she doesn't harm herself while she performs her Craft. It would be too easy for a Healer to completely drain herself in seeking a healing, as their self preservation instinct suffers.
Healer Queens are the most common dual-caste for females.