Most plants live life in the slow lane, but some can move with incredible speed. The bladderworts, a group of flesh-eating water plants found all over the world, have underwater traps that can catch and kill microscopic animals. The traps (or bladders) close too quickly for the naked eye to follow. But Olivier Vincent from the University of Grenoble only managed to work out how they work by filming them with high-speed cameras.
The bladderwort sets its traps by pumping out the water inside them. The water pressure falls inside the traps and their elastic walls buckle inwards, storing energy like a coiled spring. A sealed door prevents any water from entering, and a long hair acts as a trigger. If an animal brushes against the hair, it breaks the seal on the door and allows water to rush inside. The springy walls bounce outwards, sucking in the surrounding water and any animals swimming within it. The door swings shut again, and the plant breaks down its captive prey with digestive enzymes.
Vincent found that the trap opens in around half a millisecond, and it closes again in around two and a half more. That’s several hundred times faster than a human blink, and 100 times faster than the snapping action of the Venus flytrap. In fact, the bladderwort’s closing trap is one of the fastest movements of any plant. It’s also completely mechanical. Once an animal hits the trigger hair, the plant does nothing. It relies on an inevitable chain of physical forces to open the trap and close it behind its prey.
Take the door – when it’s closed, it bulges outwards but a push from the trigger hair deforms it slightly. This change in shape spreads throughout the door allowing more and more water past it and eventually inverting it altogether. Only when the water pressure inside the trap matches that outside it does the door swings back into place and resume its original shape.
Reference: Vincent, Weibkopf, Poppinga, Masselter, Speck, Joyeux, Quilliet & Marmottant. Ultra-fast underwater suction traps. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.2292