How Darwin opened a can of worms in New Zealand's soil

OPINION: Charles Darwin wrote a 300-page book about earthworms. Among other things he reported that, through their burrowing into the soil and throwing up castings, earthworms slowly bury stones or other objects on the surface.

Earthworms completely buried a flagstone pathway across his lawn as they did other stones Darwin watched for many years. He calculated the number and weight of worms per acre in English and French soils and measured the depth to which the worms buried the stones. He also measured how deeply worms had buried tile floors, pediments and walls of old Roman villas, abbey ruins, arrowheads, weapons from medieval battlefields and old coins in Britain and elsewhere and checked the sinking slabs at Stonehenge.

Everywhere he looked the earthworms had done their stuff, burying not just stones and old coins but whole cities and civilisations. Darwin thought that archaeologists should be grateful to earthworms for burying and preserving so much of our past.

On reading Darwin's book, an Auckland sceptic, Mr Urquhart, questioned his claims and set about repeating his experiments. He was astonished to find nearly four times as many earthworms in New Zealand soil than in any English soils and that they buried things much faster here than in Britain. Subsequently, several scientists have confirmed the great abundance of earthworms in New Zealand soils. Our best soils have up to 1000 worms per square metre, or 10 million per hectare, but repeated ploughing cuts back their numbers. Polly McColl figured that 800 kilograms of sheep grazed on a one-hectare field near Martinborough while up to 3000kg of earthworms burrowed away under their feet.

Similarly, the biomass of earthworms under the bush in the Orongorongo Valley was far greater than the biomass of possums and all other animals living above them. Dr Gregor Yeates found that earthworms near Upper Hutt buried coils of wire in about a year.

These worms are all foreigners, accidentally brought from Britain long ago. British worms find New Zealand very much to their liking and turn over up to 100 tonnes of soil per hectare every year on many farms.

However, New Zealand has a rich fauna of native earthworms. Some of our 170-odd species grow to nearly a metre long and are as thick as a man's thumb. You must dig deep to find them. If you damage our native worms, most of them exude a milky liquid, which is why they are sometimes called milk worms. Curiously, the milk fluoresces in the dark. Nobody knows what purpose the light serves, but Maori turned it to their advantage, using the worms as fishing bait.

Our native earthworms burrow in bush soils and most disappeared as large parts of the country were turned into farmland.

However, some big native worms survive deep under pasture and are occasionally unearthed by astonished suburban gardeners. I'd be interested to hear if you have turned up any of these big native worms round Wellington.

- © Fairfax NZ News

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Ollie   #1   11:39 pm Mar 11 2010

About 20 years ago I was digging out a large and very old blackberry in my garden in Berhampore and came across some long white worms as you describe and yes I was truly astonished. I had no idea what they were and in those pre Google days ahd to search them out in the library

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