The Book of the Earthworm

by Sally Coulthard

  THE BOOK

  OF THE

  EARTHWORM

  An Apollo book

  First published in the UK in 2021 by Head of Zeus Ltd

  Copyright © Sally Coulthard, 2021

  The moral right of Sally Coulthard to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act of 1988.

  All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of both the copyright owner and the above publisher of this book.

  A catalogue record for this book is available from the British Library.

  ISBN (HB): 9781789544756

  ISBN (E): 9781789544749

  Linocuts © Sarah Price

  Head of Zeus Ltd

  First Floor East

  5–8 Hardwick Street

  London EC1R 4RG

  www.headofzeus.com

  THE BOOK

  OF THE

  EARTHWORM

  SALLY

  COULTHARD

  AN APOLLO BOOK

  www.headofzeus.com

  CONTENTS

  Copyright

  Title Page

  Epigraph

  Introduction

  Earthworms and us

  The three types of earthworm

  The earthworm community

  Record-breaking earthworms

  When did earthworms evolve?

  Would humans survive if earthworms went extinct?

  Earthworms and seeds

  Are earthworms in trouble?

  How does a decline in earthworms affect us?

  What’s worm-friendly farming?

  Do earthworms affect climate change?

  Earthworms and space travel

  Why are worms called ‘worms’?

  Why was Darwin fascinated with earthworms?

  Can you eat earthworms?

  Why do some people think earthworms are disgusting?

  Earthworm ‘cures’

  The earthworm’s body

  Can earthworms see?

  Why do earthworms squirm in daylight?

  Which end of an earthworm is which?

  How do earthworms move?

  How strong is an earthworm?

  How fast can an earthworm travel?

  Do worms have taste buds?

  Can earthworms survive underwater?

  Why are earthworms slimy?

  Can earthworms hear?

  Can an earthworm regrow if it’s cut in half?

  Earthworm behaviour

  Why do earthworms surface after rain?

  Why is it difficult to pull an earthworm out of a hole?

  Do earthworms like warm or cold weather?

  What do earthworms eat?

  Do earthworms build homes underground?

  Are earthworms territorial?

  What animals eat earthworms?

  Can earthworms defend themselves?

  How do earthworms have sex?

  Can you train a worm?

  Do earthworms sleep?

  Do earthworms make any noises?

  Do earthworms make friends?

  Do earthworms take risks?

  How long do earthworms live?

  Do earthworms experience pain?

  Endnotes

  About the Author

  An Invitation from the Publisher

  …love for all living creatures, the most noble attribute of man.

  Charles Darwin, The Descent of Man (1871)

  Introduction

  When Charles Darwin had to pick what he thought was the most important animal in the world, he didn’t choose the ape for its intelligence, or the sheep for its usefulness, or the duck-billed platypus for its sheer oddness. He chose the earthworm.

  Calling it ‘nature’s plough’, Darwin crowned the humble earthworm the most significant creature on the planet, stating: ‘It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.’ Two thousand years earlier, Greek philosopher Aristotle had hailed worms as the ‘entrails of earth’.*

  And yet, most of us know almost nothing about these marvellous engineers of the soil. We take them for granted, but without earthworms, life would stop. The world’s soil would be barren – our gardens, fields and farms wouldn’t be able to grow the food and support the crops and animals we need to survive. Earthworms not only recycle decaying plants, putting nutrients back into the soil, but also, with their endless wiggling and burrowing, they help rain soak away and provide food for wildlife as diverse as foxes and frogs. Recent research even suggests earthworms can help clean up polluted land, turning it back into rich, fertile ground.

  Earthworms are heroes in miniature. Many of our current environmental issues can seem overwhelming and yet, ironically, some of the solutions may lie in one of nature’s smallest, most overlooked creatures. For too long we have taken the endless toil of earthworms for granted, without really knowing who’s doing all the work, or why.

  Leonardo da Vinci famously declared: ‘We know more about the movement of celestial bodies than about the soil underfoot.’ Everyone should know what’s going on under their back gardens. It’s miraculous.

  * Aristotle never actually calls earthworms the ‘intestines of the soil’, as is often misquoted. In De Generatione Animalium (On the Generation of Animals), Book III, translated by Arthur Platt (1910), he writes: ‘For all of these [animals], though they have but little blood by nature, are nevertheless sanguine, and have a heart with blood in it as the origin of the parts; and the so-called “entrails of earth”.’

  Earthworms and us

  The tulip and the butterfly

  Appear in gayer coats than I

  Let me be dressed as fine as I will,

  Flies, worms, and flowers, exceed me still.

  Isaac Watts, Divine Songs (1715)

  One of the most remarkable things about the earthworm is just how little we really know about this extraordinary creature. For one of the most important animals on the planet, it has been merrily ignored for much of its existence.

  Until about thirty years ago, only a few dedicated scientists had ever studied this amazing organism, but in recent years an increasing number of people are waking up to just how critical earthworms are to our entire ecological system. In particular, people have been looking at the potential of earthworms in sustainable farming practices – such as vermiculture (getting worms to make fertiliser) and organic waste recycling – and, perhaps more surprisingly, as a source of high-protein food (see Can you eat earthworms? page 44).

  Other research projects have investigated the role of earthworms in restoring polluting or degraded farmland and environmental monitoring. The earthworm, whether it likes it or not, has been dragged centre stage. Only now are we starting to learn just what a valuable creature the earthworm really is.

  Perhaps the first thing to say is that there isn’t just one type of earthworm. In fact, there are thousands. Across the world, there are thought to be at least 3,000 different species of earthworm, but because they’ve been so little studied, there are probably thousands more than that, tucked away and yet to be discovered.

  Earthworms also come in a wide variety of sizes. Different species can range in length from a centimetre to a gigantic 3 metres. Their colours vary enormously, too – alongside the muted browns and pinks we are familiar with in our own back gardens, some earthworms are green, stripy red and even a gorgeous purply blue.

  The collective noun for earthworms is a ‘clew’; clew is an
ancient relic of the Old English cliwen and means ‘ball of yarn or thread’. Other names for a group of worms include a mouthful, bed, clat, bunch and squirm.

  THE THREE TYPES OF EARTHWORM

  Who really respects the earthworm,

  the farmworker far under the grass in the soil.

  He keeps the earth always changing.

  He works entirely full of soil,

  speechless with soil, and blind.

  Harry Edmund Martinson, The Earthworm (trans. Robert Bly)

  For all their glorious variety, it’s helpful to divide earthworms into three groups. These categories are roughly based on whereabouts in the soil the earthworm lives, and how it feeds and burrows. Starting from the surface, moving down into the soil, you’ll discover:

  SURFACE DWELLERS (Epigeic) – this group of earthworms doesn’t actually live in the soil. Instead, it rummages around on the surface among moist, warm, decomposing leaves and organic matter. These earthworms feed on this decaying material and on the fungi and bacteria that help break it down. They tend to be small (around 3–4 centimetres long), don’t burrow into the ground, and are often red or reddish brown in colour.

  Earthworms in this category include the wonderfully stripy Tiger worms (Eisenia fetida), which often live in compost heaps and are also known as Redworms or Red Wrigglers. You don’t find many of these worms on agricultural land because of the lack of any permanent leaf litter; they tend, instead, to prefer grasslands and forests.

  SHALLOW BURROWERS (Endogeic) – this second group of earthworms lives in the soil but usually stays in the upper layers (to a depth of around 30 centimetres). They feed on the dead leaves, fungi and tiny creatures that are already mixed into that shallow layer of earth. Endogeic worms also burrow horizontally in the soil, creating a branch-like network of tunnels, and tend to be medium-sized (around 8–14 centimetres long) and very pale in colour (such as pinks, greens and blue-greys).

  DEEP BURROWERS (Anecic) – this third group of earthworms is the largest in length and can dig as far as 3 metres down into the soil. They burrow in straight vertical lines – rather like an elevator shaft – coming up to the surface at night-time to grab plant material for food, which they pull down into their burrows. They are also red or brown in colour but usually have a darker head and lighter-coloured tail. These are also the earthworms that leave little heaps of soily poo on the surface of your lawn – these piles are called ‘worm casts’.

  Of all the deep burrowers, the best known is the Common earthworm (Lumbricus terrestris). This is the gardener’s friend – also known as the lob worm, the night crawler, the granddaddy worm and the dew worm – and is the largest naturally occurring earthworm across most of Europe (around 9–30 centimetres). The body of the Common earthworm can be as thick as a pencil and its tail can be flattened into a paddle shape, to help the earthworm grip the sides of its burrow.

  THE EARTHWORM COMMUNITY

  In reality, nature is never tidy. The three categories of earthworm are useful but, out in the field, the boundaries between different species of earthworms can get a bit blurred. For example, compost worms – such as the stripy Tiger worms (Eisenia fetida) – are sometimes put into their own separate category, distinct from other surface-dwelling epigeic worms. Other worm experts like to separate shallow-burrowing earthworms into three distinct groups of their own, depending on how deep they live in the soil and what they eat.

  Neat categories suit scientists in labs, but earthworm behaviour isn’t entirely fixed; populations can, to a certain extent, adapt their behaviour according to their environment. This ecological plasticity means that the same species of earthworm can display different behaviours or morphological characteristics in different local environments. In the northern hemisphere, for example, the widely abundant Grey worm (Aporrectodea caliginosa) is a shallow burrower, making short, horizontal burrows. The same worm in the southern hemisphere makes long, vertical burrows, just like a Common earthworm (Lumbricus terrestris), and behaves more like a deep-burrowing species.

  Few studies have managed to establish the ratio of earthworms we have in the soil – i.e., do we have more surface dwellers than deep burrowers? A Natural England survey,1 however, attempted to find out what kinds of earthworms lived where.

  By far the biggest group of earthworms was the shallow burrowers, making up around three-quarters of all the worms they found. Surface dwellers made up the next largest group – around a fifth of all the earthworms – and the deep burrowers just one in twenty. The different species of earthworms don’t seem to bother each other – depending on the habitat, communities of up to fifteen different species of earthworm rub along nicely together, happily coexisting within the same ecological niche.2

  The so-called Common earthworm, it turns out, isn’t that common. For such a well-known earthworm, it would seem that it only accounts for about one in every eighty of the earthworms under our feet. The small, shallow-burrowing Grey worm, by contrast, made up over a third of the species found in the Natural England survey. You’ll recognise a Grey worm if you see one – it’s beautifully shaded, like a decorator’s colour card, graduating from a red head through to a pale pink middle and a purply-grey tail.

  No one is exactly sure how many earthworms there are in the soil. Recent estimates, however, suggest that even poor soil may have 250,000 earthworms per acre, while good-quality soil can have closer to 1.75 million wrigglers per acre.

  (Source: Country Life magazine)

  RECORD-BREAKING EARTHWORMS

  These worms seem to abound more in ground which is lightly tilled, than in such as has been well worked; but in lay ground they seem to be more numerous than any where else…

  The Commercial Agricultural and Manufacturer’s Magazine, Volume 6 (1802)

  The largest Common earthworm (Lumbricus terrestris) ever recorded in the UK wriggled its way into the record books measuring 40 centimetres in length and weighed a meaty five times more than the average earthworm. ‘Dave the Earthworm’ was discovered in an English vegetable patch and is now permanently preserved for posterity in London’s Natural History Museum’s collection.

  Dave, however, was a tiddler compared to the world’s largest species. One of these is Australia’s Giant Gippsland earthworm (Megascolides australis). Found only in the Bass River Valley in the south-eastern state of Victoria, this gentle giant measures, on average, a metre long and a chunky 2 centimetres in diameter. Giant Gippsland earthworms can live for five years or more, slowly pushing their way through the wet clay subsoils of riverbanks. The longer they live, the bigger they get; older specimens have been known to mature to drainpipe proportions of 3 metres.

  The record for the longest earthworm ever found belongs to a species called the African Giant earthworm (Microchaetus rappi). In 1967, a huge specimen was found on a road between Alice and King William’s Town, in South Africa. The average length of the Microchaetus rappi is usually around 1.8 metres, but this particular earthworm measured 6.7 metres long and 2 centimetres wide – the same length as the average height of a giraffe.

  Earthworms seem to thrive and grow to larger sizes in undisturbed ground. A recent study found a large concentration of whoppers on the Scottish Isle of Rum.3 A team of scientists discovered that the tiny island, which is also a nature reserve, had one particular location where Common earthworms had an average weight of around 12 grams, which is three times heavier than Common earthworms in other parts of the UK. The protected habitat of the island, which has plentiful organic matter, also lacks many of the mammals that usually devour earthworms, such as badgers, moles or hedgehogs. The area where the earthworms were found also happened to have an unusually high number of blood-sucking parasitic ticks, which discouraged people from ever attempting to settle and farm the land. Left alone, unchallenged by human activity or predation, the Rum earthworms could grow older, and subsequently larger, than in any other part of the country.

  The World Record for ‘Most Worms Charmed’ at the World Wor
m Charming Championships was 567 in half an hour and achieved, rather brilliantly, by a ten-year-old girl called Sophie Smith.

  WHEN DID EARTHWORMS EVOLVE?

  When dinosaurs were crashing around on the surface of the Earth, the lowly earthworm was already wriggling around underneath their feet. Recent analysis has discovered that the common ancestor to all earthworms lived at least 209 million years ago.

  At this time, the world didn’t have seven separate continents, but rather one massive supercontinent called Pangaea. When this vast, consolidated land mass began to split apart – about 180 million years ago – earthworms were carried off to the furthest reaches of the planet and evolved into the thousands of different species we see today. Antarctica is the only continent that doesn’t currently have a species of earthworm, although earthworms probably did once live there until the continent’s drift southwards made the land too cold for them to survive.

  Continental Europe has about two hundred different species. Britain by itself doesn’t have a vast number of native earthworms – twenty-six species at the last count. It’s thought that during the last Ice Age, the existing earthworms in Britain were killed off. When the glaciers finally retreated, earthworms from the warmer parts of Europe began to move northwards, eventually reaching Britain by crossing the land bridge that then connected the east coast to the European mainland. So, all Britain’s earthworms are, in fact, European.

  WOULD HUMANS SURVIVE IF WORMS WENT EXTINCT?

  The nation that destroys its soils destroys itself.

  Franklin D. Roosevelt, Letter to all State Governors on a Uniform Soil Conservation Law (1937)