How the Venus flytrap snaps up its prey
American and French scientists believed they have explained how one of nature's marvels, the Venus flytrap, snaps shut to snare its victims.
The plant -- described by Charles Darwin as "one of the most wonderful in the world" -- is able to enclose a fly within its clamshell-shaped leaves in just 100 milliseconds, faster than the eye can blink.
Scientists have long wondered how the flytrap (Latin name Dionaea muscipula) is able to do this spectacular feat, given that it does not have the nerves and muscles of fast-moving animals.
The answer, according to a study published on Thursday, is tensile strength.
The plant first bends back its rubbery leaves so that they are convex-shaped, rather like half a tennis ball that has been flipped inside-out.
To close the trap, the plant releases the tensed-up energy.
The leaves instantly flip from convex to concave -- as if the half tennis ball has suddenly popped back to its normal shape. Their edges snap together and the insect is trapped within.
"Closure is characterised by the slow storage of elastic energy followed by its release," say the authors, led by Lakshminarayanan Mahadevan, an Indian-born professor of applied mathematics and evolutionary biology at Harvard University.
The researchers were able to model the change in geometry by putting microscopic dots of ultraviolet fluorescent paint on the external surface of the leaves.
They then filmed the closure under ultraviolet light, using a high-speed video at 400 frames per second, which showed the leaves' sudden shift from convex to concave when the trap closed.
Previous work has already established that the flytrap lures the insect with a smell exuded from the inner surface of the leaf. When the fly walks on the surface, this activates a hair trigger and causes closure.
Still to be explained is the phase in between -- exactly how the signal is transmitted from the hair trigger to the closure mechanism in such an astonishingly fast time.
The study appears in Nature, the weekly British science journal.