inquiline

in·qui·line

noun \ˈin-kwə-ˌlīn, ˈiŋ-, -lən\

Definition of INQUILINE

: an animal (as the house mouse) that lives habitually in the nest or abode (as a human dwelling) of some other species

—in·qui·lin·ism \-lə-ˌniz-əm\ noun