Study Finds Pitcher Plants Switch Off Traps to Capture More Ants

Posted on January 24, 2015

Ant on a pitcher plant in Borneo

Researchers from the University of Bristol and the University of Cambridge have discovered the pitcher plants temporarily switch off their traps in order to capture more ants. The plants have slippery pitfall traps that cause ants to slide down into the bottom where they are dissolved in a liquid called phytotelma.

The researchers surveyed Nepenthes pitcher plants in Borneo. They found that the slippery slide inside the plants that sends ants to their doom can go dry for up to eight hours a day. When the trapping surface of the plant is dry it is easy for ants to walk along it and gather sweet nectar. However, the plant does not capture very many insects when the trap is not set. When the trap is wet again the slippery trap returns and the ants fall to the bottom.

The researchers also found that the traps would sporadically capture large batches of ants from the same species. The researchers conducted tests where they artificially kept the pitcher plant traps wet all the time. They found the constantly wet plants - with their traps always set - failed to capture large batches of ants. The scientists theorize that a pitcher plant that is constantly wet will capture important scout ants making it impossible for them to return to the nest and inform the other ants about the delicious nectar it discovered. By occasionally turning off its trap a pitcher plant is able to lure more ants to its trap through these scout ants.

Dr. Ulrike Bauer from Bristol's School of Biological Sciences, says in a statement, "By 'switching off' their traps for part of the day, pitcher plants ensure that scout ants can return safely to the colony and recruit nest-mates to the trap. Later, when the pitcher becomes wet, these followers get caught in one sweep. What looks like a disadvantage at first sight, turns out to be a clever strategy to exploit the recruitment behaviour of social insects."

A research paper on the study can be found here in the journal, Proceedings of the Royal Society B.

Photo: Dr. Ulrike Bauer