A preying mantis is a woman who, while orally pleasuring a man, bites the head of the penis right when the man is about to cum, much like the female insect (preying mantis) will eat her mate after thereproduction process.
Guy 1: Dude why is there blood on your pants?
Guy 2: Because that bitch is a preying mantis, she bit the head of my dick!
The act of walking around a night club or other social setting and scanning the room for the opposite sex to approach and begin seducing. This behavior is very obvious to others and the body language of the subject looks like that of a wild predator looking around for a viable prey.