Tuesday, April 17, 2012

Sparkly but lethal: the sundews

The sundews, Drosera spp., set a wholly different sort of booby-trap for their prey. They do not move to trap it, not as dramatically as Venus flytraps do, but like Venus flytraps they depend on the hapless insect landing directly on their leaves.

Those leaves are beautiful, to the unwary: they sparkle in the light, giving the genus its common name. Those drops of liquid on their little stalks aren't just dew, though. For one thing, they're nectar-like, full of tasty sugar. Any hapless insect that lands to sip the bounty, though, will find out something else about them: they're sticky.

A Drosera capensis leaf bending to surround
and digest a trapped fly. Normally the leaves
are more or less straight.
A bug tricked into landing on a sundew leaf is quickly and effectively glued down, unable to free itself. Even if it only brushed one sticky droplet, the stalks bearing other droplets -- appropriately known as tentacles -- move towards it, glomming many other droplets onto its body. Some sundews can snap these tentacles into place in fractions of a second, faster than any prey can respond.

The prey's futile struggles inevitably kill it, either through exhaustion or through suffocation as the sticky lures clog its breathing. Slowly, then, the tentacles begin to tug on its body. The leaf curls inward around its trapped insect, and the glands that secreted the sugary lure start to secrete digestive enzymes. The prey is reduced to a nutrient soup, which the plant absorbs through other glands on the leaf surface. Dinnertime for the sundew.

Like all carnivores, though, these plants aren't being vicious. Drosera roots are effectively useless for nutrient uptake: without the nutrients they capture from their prey, they would sicken and die very quickly. It's all perfectly natural -- beautiful, even, in the fierce and sharp-edged way that nature so often is.

Image source: Elhardt, Noah. Drosera capensis bend. Retrieved April 16, 2012, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:Drosera_capensis_bend.JPG>

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