Carnivorous plants like the Venus flytrap use a counting system to catch their prey and avoid false alarms, a new study shows.
The plants rely on insects to survive in their normally nutrient-poor soils. To trap their prey they emit a fruity scent to lure insects.
A study published in Current Biology today looked at how the plants know when they've ensnared their latest meal or decide to keep their traps shut to produce their acidic enzymes used to digest their prey.
"The carnivorous plant Dionaea muscipula, also known as Venus flytrap, can count how often it has been touched by an insect visiting its capture organ in order to trap and consume the animal prey," study author Rainer Hedrich of Universität Würzburg in Germany says.
Researchers tricked the plants into thinking something had landed on it by increasing the number of mechano-electric stimuli to their trap and monitoring the response.
It found a single touch puts the plant in a 'ready-to-go' mode where it is ready to close, but is aware it could be a one-off.
A second touch makes the trap close and as the prey struggle and squirms to get out and continues to touch the trigger hairs over and over, it only "excites" the plant.
By now, the plant begins to produce a special touch hormone and after five triggers, glands on the inner surface of the trap start producing digestive enzymes and transporters to absorb the nutrients.
Hedrich has labelled this a "deadly spiral of capture and disintegration" and means the plant produces the right amount of enzymes depending on the size of the catch.
Hedrich says that allows the Venus flytrap to "balance the cost and benefit of hunting".
The plants also show a marked increase in production of transport that allows them to take in sodium. Though it is unclear why, researchers say it could have something to do with how the plant keeps the right balance of water inside their cell walls.