What prompts plants to set traps? | Eye News

There is something inherently underhand about traps, yet deliciously wicked, especially when the victim is bigger and stronger than you and has been picking on you. I’m not sure for how long we’ve been setting traps, both for ourselves and for animals, but I would not be surprised if very primitive us were inspired by what we saw was going on in the natural world, where both plants and animals have been setting and springing traps for one another for aeons.

One question that has begun to bother me a bit is this: do they know what they are doing is inherently underhand, even evil maybe? We are now declaring so many animals – and even some insects – to be sentient. Does this extend to knowing the difference between right and wrong? And if, as is being claimed, plants can feel ‘happy’ when they hear classical music and appreciate soothing compliments, do some of them smile when they trap their victims?

Of course the underlying justification for their behaviour is that most of them grow in areas where the soil is poor and they cannot (or are unable to) get the nitrogen they need from the soil, so they have taken to trapping insects and even small mammals and birds to make good the shortage. Perhaps they have a stronger case than animals – which can chase their prey – because plants can’t move (at least not quickly enough), so must lure their victims to them. And some of the traps they have evolved to do so are pure evil genius.

My favourite has got to be that of the Venus flytrap, found in the subtropical wetlands on the east coast of North America The terminal part of the leaf of this plant that forms the trap is hinged along the midrib, with the two lobes, armed with spikes leaning towards one another. Trigger hairs along the inside of the ‘trap’ are sensitive to touch. Along comes a spider or fly, brushes against the hair – and nothing happens. But only for anything between 0.5 and 30 seconds maybe, because a timer has been set off by the first trigger-hair. If the victim disturbs another hair within this period, the two diabolically armed lobes snap shut instantaneously, caging the buzzing insect.

Some kind of electric switch gets thrown, snapping shut the trap in under a second. The grace period is given to reassure the plant that what set off the first trigger was something alive and worth trapping, and not say a falling leaf. Even after the trap closes, the plant waits for more trigger hairs to be disturbed as the victim buzzes and fizzes furiously inside trying to escape. This reassures the plant that it has truly claimed a meal worth digesting, and now it hermetically seals the lobes, turning the leaf into a stomach in which its meal is digested. After 10 days, the lobes reopen and all that remains is a husk. Each trap can only work four or five times before the leaf dies. It’s also been called the bear-trap, or mouse-trap or man-trap – all inaccurate because mercifully the plant does not trap either mice, men or bears!

Whilst we’re talking about traps and lures, can bribes be far behind? Pitcher plants use sweet nectar and brightly coloured patterns to lure insects inside the rolled up leaves which form the ‘pitcher’. The inner walls are waxy and slippery as a skating rink, and right at the bottom of the leaf is a well filled with digestive enzymes waiting. Insects lose their footing and slide right down, and that’s that.

Perhaps, even more wicked is the cobra plant (another native of North America), whose leaves rise up to resemble a striking cobra, complete with a hood and an alluring (to insects) looking forked tongue. The top of the hood is splotched with chlorophyll-free patches – which one could say, resemble skylights. The entrance to the tube, inside which the victim thinks all the goodies are, is a tiny hole, the walls slippery and lined with downward pointing hairs. In goes the ant, and then wanting to get out looks up and is confused by all the ‘skylights’ in the hood (which also conceals the actual entrance), checking them one by one and tiring itself out before losing its grip and falling to the bottom, assisted by the downward pointing hairs that line the walls of the tube.

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The nearly 200 species of sundew are found in bogs all over the world, except Antarctica, and are wholly reliant on an insect diet for their nutrition. Their leaves are rimmed with long tentacles, tipped with shiny pearl like beads of sticky, sweet glue, something no bee or fly or any other insect can resist. They land, get stuck, struggle, only to be more tenaciously held, and eventually die either of exhaustion or asphyxiation as the tentacles close over them and wrap them up and the digestive juices get to work.

Then, there’s the one and only bladderwort that creates — of all things – a vacuum into which it sucks its victims. Both terrestrial and aquatic varieties exist worldwide, and they trap their prey by means of an aquatic bladder, which is negatively charged, its entrance sealed by a trapdoor, but hair-triggered to open when prey disturb the trip lines. The negative charge inside, causes water to leach out and a vacuum to be formed. The trapdoor opens, the victim and water is sucked in and the door is closed all in 1/35th of a second!

Bribery. Deception. Impalement. Acid bath immersions. Evolution can be so innocent!

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