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Warning: these plants eat meat

Just be thankful theyíre small, says Peter Marren. These plants can wipe out millions of insects in a single summerís day

If we didn’t have sundews and pitcherplants as living examples, the idea of a carnivorous plant would sound like science fiction, about as improbable as an animal with leaves. Plants just don’t seem designed to eat meat. They have no teeth to start with, nor a stomach to hold the food while it is digested. They have no legs to run after their prey, nor, for that matter, any eyes to spot the prey in the first place. Plants, so zoologists claim, exist in order to be eaten by animals. Well, a sundew, if it had a brain, would beg to differ.

For a flowering plant to eat meat, certain modifications to the basic design of roots, stems and leaves are needed. Since, despite John Wyndham’s triffids, no plant has ever been able to pull up its roots and walk, it needs some means of attracting and then trapping animals. It also needs a cocktail of corrosive fluids to break down meat into its component sugars and proteins. And even if a plant cannot have a stomach, it will nonetheless need some sort of enclosed breadbasket to bring the food into contact with digestive glands embedded in the leaf.

F ortunately attracting insects comes naturally to a flowering plant. Scents, colours and guide-marks all help to lead the insect to its sugary reward, whilst the flower quietly dumps a load of pollen on its back. Some flowers, like the catchflies, trap the insect for a time to ensure it does its unwitting job properly. Sometimes the insect stays trapped and dies. Though this is an occupational hazard of a pollinator, these insects do not become food for the flower. No flower, in fact, can kill and then eat an insect. Because they need to be light enough to be carried on a thin stalk, they cannot afford to carry the necessary glands and glues. Instead, carnivorous plants turn to those tough, versatile workhorses, their leaves.

Sundews are our best-known meat-eating plants. Their red, jewel-like leaves use bright colours and twinkling droplets of goo to attract their prey and then seize hold of it with the combined powers of superglue and acid. Butterworts work in much the same way, using their thick, sticky leaves to trap small insects. Both kinds of leaf are sensitive, and use speeded-up growth to curl around larger prey to form a sort of vegetable stomach. A large sundew can digest insects as big as butterflies and damselflies. Our third group of native meat-eaters, the aquatic bladderworts, are really stripped-down plants, lacking roots and true stems, while even the leaves are reduced to threads. Apart from their occasional yellow flowers, bladderworts look more like floating algae than a vascular plant. They do, however, have inbuilt
‘stomachs’ in the form of tiny bladders, scattered among the

leaves, which have the power to suck in water-fleas and other tiny animals. A bladderwort plant can consume up to a quarter of a million of them in a single season.

These un-plantlike modifications come at a price. While orthodox plants devote nearly all their energy into producing leaves and flowers, carnivorous plants have to devote most of it to building their traps. However deadly they are to flies and water-fleas, their ‘business plan’ means they are less efficient than other plants, with feeble roots, and are able to flower only when things are going well. Sundews and butterworts cannot grow in grass or dense vegetation, nor indeed in fertile soil. Their compromising life-style confines them to wet, infertile places with no over-shading growth. Their idea of a perfect home is a peat-bog with no soil but plenty of moss cushions and shallow, acidic pools. Damage or remove the bog and you destroy the abode of Britain’s three species of sundew, two kinds of butterwort (plus a third in Ireland) and six bladderworts (the species are relatively few, but even so we are in the European big league for meat-eating plants).

Our carnivorous plants are, alas, among the most rapidly declining plants, not only in Britain but in Europe as a whole. The new Atlas of the Flora of Britain and Ireland will show that the range of some species has contracted by up to a half within living memory. The most obvious reason is habitat destruction. You would need to be a very cunning bladderwort to survive at England’s largest lowland bog, the much-abused Thorne Moors. More insidious is the enrichment of much of our soil and freshwater with nitrogen and phosphorus. Enriched conditions produce lusher vegetation, murky water and increased fungal attack, all of which spell doom for meat-eating plants. Fortunately they seem safe enough for the moment in their heartlands, the blanket bogs of north-west Britain.

Where they still occur, carnivorous plants can dominate their patch. In places like the New Forest you can count several hundred sundew plants in a square metre, or scoop up handfuls of filmy bladderwort. The number of insects they consume, wrote Darwin, must be prodigious. Yes, indeed. A Norfolk naturalist, F.W. Oliver, once witnessed the result of a vast swarm of migrant butterflies that had fatally settled to feed on what they took to be drops of nectar, candy from the Gods. It was, in fact, a large patch of great sundew Drosera anglica. Soon all that was left were pairs of white wings, stuck to the leaves and painting the ground white. Oliver estimated that six million butterflies had been caught and consumed within shortly after dawn on that hot summer’s day. They might not run, jump and snap their teeth, but there are times when plants can teach the animals a thing or two about appetite. It should make us thankful that chemistry prevents them from growing to the size of tigers, or oak trees.

 Reproduced from
Plantlife magazine
with permission

Peter Marren
is a member of Plantlifeís Advisory Council and author of many books including Britainís Rare Flowers.