Tricky pitcher plants lure ants into a false sense of security

In a counterintuitive twist, pitcher plant traps that work only some of the time did the best job of catching huge hauls of ants for the plants to eat. A group of Nepenthes rafflesiana outperformed plants that researchers kept artificially ready to kill, catching more than twice as many ants in an experiment by taking advantage of the insects’ food foraging habits, says Ulrike Bauer of the University of Bristol.

When the funnel-shaped leaves of mature plants dry out at the nectar-coated collar, ants scouting for food can scurry safely over them without slipping into the trap. The scouts then leave trails that nest mates follow to the nectar, and when rain or dew moistens the collar again, the followers slip to their death. By “waiting” for scout ants to recruit nest mates, pitcher plants exploit the

social habits of ants and score big meals, Bauer and her colleagues say January 14 in Proceedings of the Roy al Society B . 

Younger plants in this and related species have a backup waxy surface that’s treacherous even when dry. But biologists have long been intrigued about why older plants rely only on pitcher traps that fail when they dry out.

To test the notion that unreliable traps might produce more prey in the end, Bauer and colleagues set up hospital drips to keep the lip wet on one trap in each of 23 pitcher plants twining through trees in a Borneo forest. For comparison, researchers monitored a trap on each plant that was left to the vagaries of natural moisture. Over several weeks, the natural pitchers caught a total of 339 ants, mostly in a few big massacres, versus the 136 total ants bagged by the group of hospital-drip-assisted pitchers.