Sticky hairs on the leaves of sundews change position in response to touch via expedient differential cell growth.
Cape Sundews Trap Bugs In A Sticky Situation
“A few leaves, however, have been turned into active traps. Sundews grow in European bogs and marshes. Three-quarters of the family live in western Australia…The leaves of all are covered with hairs that on the outer margins may be half an inch long. Each of them, provided that the weather is not too dry, carries on its tip a glistening sticky bead…Insects too must find them attractive, for in spite of the fact that these leaves carry no enticements of nectar, insects are drawn to them. When one alights, it inevitably sticks to a hair. As it struggles, it touches other hairs and becomes further entangled. Neighbouring hairs, even if they have not been touched, are able to sense that a catch has been made and they bend towards it. If the insect is a large one and has been caught near the edge of the leaf, the hairs will lean over and convey the captive towards the centre. There, a whole group of hairs arch over it. The glistening beads contain not only glue but a digestive fluid that soon begins to dissolve the insect’s body. The hairs then start to absorb their victim’s substance. If the captured insect is particularly large, the whole leaf may fold to enclose it and complete the process.
“These movements of the hairs are achieved by a swift differential growth of the cells of one side. Once initiated, this proceeds at an extraordinary speed. An outward pointing hair can turn through 180 degrees to point inwards in less than a minute.” (Attenborough 1995:81-83)
