Springing the trap

Charles Darwin is known the world over as the founder (along with A R Wallace) of modern evolutionary biology. But he wrote a great many books besides The Origin of Species, and all of them illuminate the astonishing ways in which evolution works. In one of those books, Insectivorous Plants, Darwin examined plants that ate animals – in contrast to the usual situation, which is the other way round. Carnivorous plants seem to violate another of nature’s rules: some of them possess the property of thigmonasty or touch-induced movement. Because they display the behaviour without nerves or muscles (though they are not unique in this; see Bonner 1994), carnivorous and sensitive plants, like the familiar Mimosa pudica (touch-me-not), raise the question of where to draw the boundary between plants and animals