Question: How does the pitcher plant Nepenthes hemsleyana facilitate roosting of mutualistic bats? Hypothesis: Pitchers have adaptations that match the shape and body size of small woolly bats. Organisms: The pitcher plant Nepenthes hemsleyana, its close relative N. rafflesiana, and the woolly bat Kerivoula hardwickii. Field sites: Peat swamps and heath forests in western Brunei Darussalam on the island of Borneo. Methods: We measured various morphological traits of N. hemsleyana that might facilitate bat roosting and compared them to pitchers of N. rafflesiana that is not visited by bats. We compared the size and characteristics of the pitchers with body sizes of roosting bats. Conclusions: As predicted, aerial pitchers matched the body size of bats and had lower digestive fluid levels than pitchers of a close relative. Thus, small morphological differences between closely related species have caused rapid dietary niche divergence.