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Why Would A Perfectly Nice Carnivorous Plant Subsist On Feces Instead Of Meat?

Pitcher plants grow on nutrient-poor soils, but whereas N. rafflesiana copes with this lack of nutrients by using fluid-filled pitchers to catch insect prey, N. hemsleyana has abandoned carnivory in favour of a unique and intimate relationship with the woolly bat. To provide the bat with an ideal roost, the pitchers of N. hemsleyana have evolved to perfectly fit the bat’s body. Unlike other pitcher plants they contain very little fluid. And most striking of all, the backwall of the pitcher forms a parabolic dish that aids the bat’s echolocation. In return for its roost, the bat hunts and pre-digests the insects, depositing them as faeces in the pitcher. To measure the costs and benefits of this mutualism, Schöner selected plants from both species in the field. When they produced new pitchers, she blocked them with cotton wool and cling-film to prevent bats or insects from entering. (Click on title for full story.)