Carnivorous plants

Articles in ‘Carnivorous plants’

How does a Cobra lily trap its prey?

March 4th, 2011

In a sun-lit meadow on the mountainside, a large grove of curving plants grow close together in the marshy grass, which glistens with cool running spring water.  Humans are struck by the resemblance of these pitcher plants to hooded cobras, poised to strike, and have christened them Cobra Lilies, but for an insect there is nothing threatening about them at all.

On the contrary, they are very enticing.  The pitcher plant surface is covered in scattered nectar glands where insects can feed, and there are even more on a bright red appendage, forked like a snake’s tongue. The tongue hangs down from a mouth-like opening, and just inside there is a particularly copious supply of the tempting sweet stuff.

For us, the snake illusion is completed by the pattern on the domed leaves, giving the impression of scales.  They are translucent aeroles that flood the pitcher with bright light. An insect might be reluctant to enter a dark interior, but is lulled into a false sense of security in this well-lit space.

Having gorged, rather than go back out the way it came in, the insect might head straight for one of these false exits.  After all, the mouth is half hidden by its curling lip.

Disorientated and tired, like a fly that has been helplessly crashing into a glass window, the insect might try to settle on the slippery walls of the plant.  Unable to get a grip, it goes plunging down the spiralling tube straight into the pool at the bottom, which is kept filled with water pumped up from the ground.  The down-pointing hairs on the inner walls discourage any attempts of a soaked insect to climb back to freedom.  By the end of the summer, these carnivorous pitcher plants will be half-filled with insect remains, the sign of a successful season.

Cobra Lilies (Darlingtonia californica) are native to northern California and southern Oregon in the United States.

The giant pitcher plant that tree shrews use as a loo: Nepenthes rajah

February 6th, 2011

There are around 100 known species of carnivorous pitcher plants (new ones are still being discovered), with the greatest diversity found in Malaysia.  These carnivorous plants grow vessels to trap their insect prey, which they attract with nectar. The victims lose their footing on the slippery walls and drown in the liquid held inside the plant, before being promptly digested.

The biggest pitcher traps are produced by Nepenthes rajah, found only on Mount Kinabalu and Mount Tamboyukon on the island of Borneo.  Its thick stems grow along the ground where the pitchers rest with their lids open, looking like elegant toilets designed by Salvador Dali. Rats, birds and frogs have been found drowned inside these giant traps, leading to dramatic headlines about rat-eating plants, but these are rare events – the plant’s main prey are insects.  However, recent studies have found that Nepenthes rajah has another source of food.

Tree shrews also come to feed on the nectar on the lid, which they reach while standing on the rim, and poo into the pitcher while eating.  So is the plant a shrew loo?  Not really, for the defecating shrew is establishing its territory, rather than fastidiously using a latrine – but for the plant it’s a great source of nitrogen.

Other interesting facts about pitcher plants

  • People have used the tough pitchers as pots for cooking rice
  • The liquid is drunk as a beverage, its taste depending on the prey the plant has caught.
  • The liquid also has medicinal uses, being used to treat coughs and bladder problems.