Pitcher plants aren’t always trying to eat. For long parts of the day, the plants ‘switch off’ their traps. Why? To capture more food.
Pitcher plants main trapping mechanism is an extremely slippery surface when wet. But, a team of scientists noticed prolonged periods where this surface was dry. “At first sight, this is puzzling because natural selection should favour traps that catch as many insects as possible,” says Dr. Ulrike Baur from Bristol’s School of Biological Sciences.
Once you understand the type of insect these plants primarily eat, the reason for the temporary off-switch becomes clear. Pitcher plants are known for capturing large groups of ants for food. The group of scientists experimented with artificially keeping the surface wet all the time. They found the traps kept wet all the time couldn’t capture as many ants.
It comes down to the social aspect of ants. Dr. Bauer explains, “Individual ‘scout’ ants search the surroundings of the nest for profitable food sources. When they find a pitcher trap full of sweet nectar, they go back to the colony and recruit many more ant workers. However, a trap that is super-slippery all the time will capture most of these scout ants and cut off its own prey supply.”
Even with no brain, pitcher plants have a “clever strategy to exploit the recruitment behavior of social insects.”
While the wax crystals are effective at all times, the peristome is only slippery when wet. A combination of hydrophilic surface chemistry and micro-topography renders the peristome fully wettable. Under humid or wet conditions, thin and stable water films form on the surface, preventing the adhesive pads of arthropods from making full contact. However, the peristome can be dry and safe to walk on for up to 8 h during the day. Variations in humidity and weather conditions act as a switch, intermittently activating and deactivating the trap.
This on/off switch is vital for pitcher plants getting the food they need. Crazy how pitcher plants evolved this strategy, isn’t it?