The medical term for the occupation and dwelling of parasites on the external skin surface is ectoparasitism.

Here's a breakdown:

* Ecto- means "outside" or "external"

* Parasitism refers to the relationship where one organism (the parasite) lives in or on another organism (the host) and benefits at the host's expense.

Therefore, ectoparasitism specifically describes the situation where parasites live on the external surface of a host's body.

Examples of ectoparasites include:

* Fleas

* Ticks

* Lice

* Mites

* Scabies mites