The worm turns

21st July 2000 at 01:00
John Stringer goes underground in search of a wriggly resource

One evening at the end of the last century, a noisy group of tail-coated scientists sat down in the entrance hall of London's Natural History Museum to a formal dinner and were served with piping hot pies - and presumably accompanying veg or a side salad. Slicing through the crust, they helped themselves to a rich gravy containing a food source that is 72 per cent fat-free protein. They were eating earthworms - a meat described by a present-day scientist as "rather better than a decent steak". History does not record the wine they chose to go with this banquet.

If that appals you, it may be because you don't know about these invaluable little animals. The earthworm is found almost everywhere, is essential to the health of our soil, is a rich source of animal protein and was described by Charles Darwin as the creature that has played "the most important part in the history of the world". His long-term studies, published in a book engagingly entitled The Formation of Vegetable Mould Through the Action of Earthworms (1881), showed that in 30 years earthworms could bury a flat stone 8cm deep. He calculated that the worms in his meadow, by their tunnelling, ingestion and egestion of earth, covered the entire field in soil to a depth of 6cm every year. He recognised the importance of worms in creating topsoil; but he didn't know enough to recognise the importance of worm action in aerating the soil and ensuring good drainage.

By dragging organic debris underground, producing a soil that is rich and plant-friendly, worms have guaranteed the success of our food crops and so our very survival. They are so good at turning over soil that they have helped preserve our history. The action of earthworms buries antiquities.

Without their busy interring of the past, all trace of Roman civilisation would have weathered away.

Success story

The earthworm is a mundane, everyday kind of creature. But it is also a natural miracle - a hugely successful animal, unchanged in millions of years and present in enormous numbers worldwide.

Darwin himself grossly underestimated the number of worms in his experimental field. He assumed that all worms produce coils on discarded earth and he simply counted worm casts to estimate numbers. There can, however, be as many as three million worms in an acre of fertile ground, covering it with around 18 tonnes of rich topsoil each year. While they may look alike, there are huge differences between species. There are 28 varieties of earthworm in Britain, of which 10 are common. Lumbricus terrestris is the UK's largest. The red worm, Eisenia fetida, is the worm of compost heaps and kitchen waste.

Deep and dark

Earthworms cannot tolerate the heat of the sun. During the summer, they may surface only at night or in heavy rain. They find it easier to get around on wet ground without drying out.

Worms are divided into a hundred or more segments. They progress with waves of movement - seven to 10 a minute - using muscle layers and bristles. They push aside the earth; if they come across compacted soil, they eat their way through. They retract bristles at the front of their body into their skin and extend it forward. These front bristles are pushed out to grip th surface and the "tail" bristles are retracted. The tail is hauled up towards the head.

Worms are very sensitive, with a high-speed nervous system for instant retraction. If a bird tries to pull them from their burrow, they extend their bristles to grip the burrow sides and cling on. They may be pulled apart in the tussle. Fortunately, they are capable of an amazing degree of regeneration. They can produce a new tail more easily than a new head - but both are possible. Red brandling worms from compost heaps can generate whole new worms from body pieces.

Earthworms are hermaphrodites; they fertilise each other. They lie side-by-side, and each forms a band around both them and the other. When the eggs are fertilised, the bands are slid from the bodies to produce egg cocoons. Young worms can be born as miniature adults, with all their segments; but some are born with few segments and add more as they grow.

Catching worms

Some species surface at night. A white light will deter them, but worms are not sensitive to red light. To catch them you need to dig down at least 30cm to find them, or water the soil, in which case they may come to the surface. Birds stamp the ground to mimic the sound of rain; and an alarm clock's drizzle-like ticking will also encourage them to surface. Worm charming is, however, best done by rocking backwards and forwards and on your toes and heels. Remember to do this lightly - stamping does not work!

WORM FACTS

* Australian earthworms are frequently up to 4m long. They sound like water running out of the bath as they vanish into their burrows.

* The world's longest worm - 6.7m - was found in the Transvaal, South Africa, in 1937.

* The biggest UK species - Lumbricus terrestris - can be 35cm, but most are 10 to 25cm long.

* A worm has been known to replace its head more than 20 times. Some worms can produce a new individual from each segment.

* One British duck farm uses earthworms to convert organic waste into compost. In Toulouse, they break down fatty factory waste before it is safely discharged into rivers.

* European settlers took earthworms to North America in the 17th and 18th century. The Ice Age had wiped out the indigenous earthworms.

* Willie was the world's most artistic worm, creating paintings by dragging his paint-soaked body across a canvas. Willie, from California, sold 200 paintings in the 1960s before retiring.

KEEPING WORMS

You can buy wormeries, but it is easy to make one:

* Sandwich a "U" of thick plastic pipe - some hose will do - between two sheets of clear plastic and wrap the whole thing with strong tape or elastic bands. Stand your wormery up and fill it with moist soil.

* Thin layers of different coloured soils are often added, so that you can see the earthworms mix them, but earthworms won't burrow through sand or chalk.

* Don't add too many worms; keep the soil moist (pierced cling film will maintain the moisture and help prevent escapes).

* Cover the sides with black paper and uncover from time to time to see how the worms are burrowing. Put the wormery somewhere cool, and feed them on leaf litter, scattered on the surface.

Watch out for the egg cocoons - the size of a rice grain, and very easy to throw out accidentally.


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