Free Darwin's Island by Steve Jones Page B

restorative drug given to Helen of Troy. Linnaeus was impressed by them: ‘What botanist would not be filled with admiration if, after a long journey, he should find this wonderful plant. In his astonishment, past ills would be forgotten when beholding this admirable work of the Creator!’ Yet another pitcher is found in Western Australia. Its traps look rather like old shoes and the plant is unrelated to any of the other pitfall-makers.
    DNA reveals some unexpected affinities among the pitchers, for the Old World kinds are in fact more related to sundews and Venus flytraps than they are to their New World equivalents. In addition they are quite close to a group of non-carnivorous lianas of tropical forests, and find more relatives in a larger class that includes rhubarbs, spinach and beet.
    An even more distinct group, the bromeliads - relatives of the pineapple and in quite a different subdivision of the kingdom from the other green carnivores - also make leafy containers that fill with water. They live in the tropical forests of the Americas. There may be more than a hundred thousand in every hectare, most of them stuck to trees. The vessels made by their fused leaves generate a huge series of tiny lakes, in which a variety of creatures find a home. At first the bromeliads appear benign, for they lack the digestive enzymes found in the other pitfalls. Tadpoles, insect larvae, twenty-five-millimetre-long salamanders and tiny crabs all live in the liquid within. In truth, they have a darker side. Each watery island is full of conflict, and their proprietors gain nitrogen from the corpses of the creatures that are killed there and are broken down by bacteria. One kind has already taken a step to true carnivory with digestive enzymes of its own.
    Other meat-eaters, unknown in the nineteenth century, are bizarre indeed. Certain soil fungi devour nematodes, worm-like creatures far larger than themselves, with a lasso that snaps shut within a tenth of a second, strangles the animal and gives the predator a rich source of food. Others do the same job with a sticky pad, while the familiar and tasty inkcap mushroom puts out spiked and lethal balls that puncture its prey and allow the fungal spores to grow within it. A hundred and fifty fungi that snack on flesh are known and there is a whole world of hunting mushrooms ready to be discovered.
    Wherever they sit in the botanical world, a hard life in a hungry place has pushed every flesh-eater towards a similar set of expedients. Like cactuses they succeed where others fail, in their case because of a shortage of food rather than of water. The cost of success is specialisation. Their habit can be expensive and their way of life fragile, for traps cost a lot and force a reduction in the investment in roots or leaves. Insectivores often find it hard to cohabit with other species, which means that vast areas are carpeted by them alone. In addition, they are forced to seek open sunlight, for their leaves are too feeble to cope with shade, and do best in places where fires sweep through and wipe out the opposition.
    The insect-eating package is sometimes lost when conditions change. Some are committed to it. The Venus flytrap is itself trapped into its narrow way of life, for it gains around three-quarters of its nitrogen from insects. The cobra lily is not far behind, and the snares of both those species are elaborate and hard to build. Other plants are more adaptable in their ways. Almost all the carnivores have some chlorophyll, the stuff that makes leaves green, but often no more than half that found in normal species. They gain some energy from the sun, albeit at reduced efficiency. The sundew and many of its fellows have reduced roots as not much food is available in their native swamps, but they can soak up a little. Radioactively labelled nitrogen shows that up to half of the nitrogen taken up by a typical individual comes from soil rather than from flesh.
    For most insectivores,