Son aquellos que viven en el exterior del huésped, generalmente sobre la piel. Ejemplos clásicos son las . Además de la irritación que causan, son vectores peligrosos que pueden transmitir virus y bacterias de un huésped a otro. El impacto en la salud humana

, which uses the concept of "parasitism" to explore class warfare. The Premise

: A poor family, the Kims, slowly infiltrates the lives of the wealthy Park family by posing as highly qualified professionals (tutors, art therapists, drivers).

: Bong Joon-ho uses architecture to show status. The Parks live in a literal high-ground oasis, while the Kims inhabit a "semi-basement" ( banjiha ) that floods with sewage.