Venus flytraps have got the number of their prey
Venus flytraps may not cry "feed me" like the man-eating plant they inspired in the movie Little Shop Of Horrors - but they can count, scientists have discovered.
The carnivorous plants, which ensnare insects with special leaves resembling spring traps, use their mathematical skill to conserve energy and avoid false alarms.
Within each "trap" there are sensitive trigger hairs that respond to the movements of a prospective meal.
Researchers in Germany learned that the Venus flytrap adjusts its feeding behaviour according to the number of times the hairs are stimulated.
"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," said lead scientist Professor Rainer Hedrich, from the University of Wurzburg.
To study what was happening, Prof Hedrich's team fooled the plants into thinking they had landed an insect by applying increasing numbers of artificial "touches" to their trap hairs.
They showed that a single touch to a trigger hair was enough to prime a trap, setting it in "ready" mode without snapping shut.
A second touch causes the trap to close around the prey which seals its fate by struggling to escape.
More touches stimulate the plant further so that after five triggers the plant begins to produce digestive enzymes and transporter molecules that take up nutrients.
The extent of the response is tailored to the number of touches received, which in turn relates to the size of the meal, the scientists found.
Prof Hedrich said: "The number of action potentials informs the plant about the size and nutrient content of the struggling prey. This allows the Venus flytrap to balance the cost and benefit of hunting."
The team, whose findings are reported in the journal Current Biology, is now attempting to map the Venus flytrap's entire genetic code. This is expected to yield more clues about how the plant has adapted to a carnivorous lifestyle.
In the 1986 film Little Shop Of Horrors, a down-trodden florist nurtures a monster plant with a taste for human flesh.
The film was adapted from a musical which in turn was based on a black comedy B-movie screened in 1960. In the original movie, the man-eating plant is created by crossing a butterwort and a Venus flytrap.