inquiline

noun2

1. •
   An animal that lives commensally in the nest, burrow, gall, or dwelling place of an animal of another species.

   • The other study[…]involved the larvae of the caterpillar Maculinea rebeli, an inquiline of Myrmica schenki. — 2003
2. •
   An organism that lives within a reservoir of water collected in the hollow of a plant stem or leaf.

   • The insect and other animal inhabitants of the pitchers, known collectively as the inquilines, may benefit the plants by breaking down prey and making nutrients available for plant absorption. — 2001