A bat sleeps inside a carnivorous plant and pays rent in droppings

Borneo's Nepenthes hemsleyana pitcher plant has largely given up digesting insects. Instead, Hardwicke's woolly bats roost inside its pitchers by day, and the plant draws up to a third of its nitrogen from their droppings -- a specially shaped patch on the pitcher even reflects bat sonar calls back like an echo beacon, helping bats find it.

— T.U. Grafe et al., A novel resource-service mutualism between bats and pitcher plants — Biology Letters, 2011