Schematic figure of sexually transmitted diseases on a two-layered network where the up and down layers represent the networks of homosexual and heterosexual individuals, respectively, and are connected by the impulsive jumping of the bisexual individuals, called propagators. The “black” nodes represent the homosexual individuals, “blue” nodes the heterosexual individuals, the “red” nodes the bisexual individuals, and the “hole” nodes are for the jumping. The solid lines represent the active links while the dashed lines denote the inactive links. Each bisexual individual has a probability p to jump to its corresponding “hole” node at each time step.