A person who pretends to be innocent, dainty, and weak (hence a dead fly), but they are actually evil backstabbers. Essentially a spanish version of a "snake in the grass." They are extremely manipulative and will have everyone fooled by their game except for the smart ones. They will usually try to make the ones who don't fall for their game look like bad people while they play the victim.
Laura had this guy so whipped. She acted like the perfect girlfriend, but behind his back she was a ho and a manipulative bitch. Laura es una mosquita muerta.