The Formation of Vegetable Mould through the Action of Worms
Encyclopedia
The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits (sometimes shortened to Worms) is an 1881
book
by Charles Darwin
on earthworms. It was his last scientific book, and was published shortly before his death (see Darwin from Insectivorous Plants to Worms
). Exploring earthworm behavior and ecology
, it continued the theme common throughout his work that gradual changes over long periods of time can lead to large and sometimes surprising consequences. It was the first significant work on soil bioturbation
, although that term was not used by Darwin (it first appeared in the soil and geomorphic literature one hundred years later).
in October 1836, Darwin was intensively occupied with further establishing his reputation as an innovative geologist
, as well as finding suitable experts to describe his natural history
collections and arranging for publication of their work as the multi-volume Zoology of the Voyage of H.M.S. Beagle
. Near the outset of the voyage he had planned a book on geology, and during it extracts from his letters on geology had been privately published by his tutor John Stevens Henslow
. Darwin now published papers on "proofs of recent elevation on the coast of Chili", "deposits containing extinct Mammalia" and "coral formations". He also rewrote his journal to incorporate observations from his notebooks as the book now called The Voyage of the Beagle
, and began brainstorming in his notebooks about transmutation of species
.
Darwin’s health suffered from the pressure of work, and on 20 September 1837 having been urged by his doctors "knock off all work" he visited his home in Shrewsbury
then went on to stay with his relatives at Maer Hall
, Staffordshire
, home of his uncle Josiah Wedgwood
. Uncle Jos pointed out an area of ground where lime
and cinders spread years previously had vanished into the soil, forming layers under a top layer of loam
. Jos suggested that this might have been the work of earthworm
s, but apparently thought that this would be of little interest to his nephew, who was working on continental scale geological problems. Actually, Charles did find it interesting and throughout his life he sustained an interest in this "unsung creature which, in its untold millions, transformed the land as the coral
polyps did the tropical sea".
He returned to London on 21 October and prepared a paper on worms forming mould. The paper on the role of earthworms in soil formation
was read out by Darwin at the Geological Society of London
on 1 November 1837. This was an uncommonly mundane subject for the society, and his peers may have hoped to hear of something more grandiose, even seeing this paper as highlighting Darwin's growing idiosyncrasies. The leading geologist William Buckland
subsequently recommended Darwin's paper for publication, praising it as "a new & important theory to explain Phenomena of universal occurrence on the surface of the Earth—in fact a new Geological Power", while rightly rejecting Darwin's suggestion that chalkland could have been formed in a similar way.
The paper appeared in the Proceedings of the Geological Society of London in 1838, and was published with a woodcut
illustration in the Transactions of the Geological Society in 1840.
“by which to work”, as his “prime hobby”. His main work on the Beagle collections continued, and in 1842 he published the first of three volumes on geology, The Structure and Distribution of Coral Reefs
. He then allowed himself to write out the first “pencil sketch” of his theory. Subsequently, in September 1842, the family moved to rural Down House
where he had space for experimental plant and animal breeding, and surroundings to observe nature. In December of that year he had a quantity of broken chalk spread over a part of a long established pasture field near the house, "for the sake of observing at some future period to what depth it would become buried."
In 1872 he was having disagreements with St George Mivart about The Descent of Man. Darwin cut communication with Mivart and went the less controversial direction of the lowly worm. His network of correspondents
and fans responded to his interest and "earthworm anecdotes began surfacing in his mountain of mail". He had been interested in earthworms "since his first fishing days at The Mount and flirting days at Maer". Still, other work constrained him. Broken off from Descent, he had to finish his next work The Expression of the Emotions in Man and Animals
.
By 1876, his first grandson
on the way, he felt his writing life was nearly over, and with so much unfinished. He wanted to write on earthworms "before joining them", but also had two more plant books in mind, and a revision of Fertilisation of Orchids
to work on. He also began an autobiographical work
intended for his family's eyes only. After turning away a request to support a controversial book on contraception (Fruits of Philosophy) - Darwin was opposed to it - he got back to work on flower
s and worms. As with much of his geological and evolution
ary work, worms were a case of gradual
, barely noticeable changes accumulating over time into large effects. He even went on a two hour excursion to Stonehenge
to see how its monoliths had been buried by earthworm castings.
He was occupied by worms at Downe
in 1880, his work coming first. He had help from the family, even receiving soil samples from Abinger
's Roman ruins. He told Vladimir Kovalevsky (his Russian translator) of slow progress with his new book.
Darwin calculated that there were 53,767 earthworms recycling away per acre
. He carried out experiment
s indoors, where they worked the earth inside pots in a worm-littered room. He experimented with stimuli at night: strong light would send them into their burrows ("like a rabbit" said Darwin's grandson Bernard), but heat and sound had no effect. Their food preferences were also tested, raw carrot
s being their favourite.
Darwin was fascinated by their behaviour
, from enjoying "the pleasure of eating" (based on their eagerness for certain foods) to their sexual passions
, "strong enough to overcome... their dread of light", even to their social feelings ("crawling over each other's bodies"). Their foraging
was especially intriguing: they dragged leaves into their burrows, pulling them in the most efficient way, by their pointed end. On these semi-intelligent creatures Darwin wrote that they obtained a "notion, however rude, of the shape of an object", perhaps by feeling it out. Worms, "five or six feet" below the ground ploughed farmers fields. Darwin felt we "ought to be grateful" to these little recyclers, which he compared to "a man... born blind and deaf". He was wondering how long it would be until he would be consumed by worms himself. It would surely be his last major work; he told German translator Victor Carus
"I have little strength & feel very old".
By 1881 he was unable to summon the strength for revisions and handed Worms on to Frank
. His health gave him troubles; he complained to his long-time friend Hooker
that he looked forward to "Down graveyard as the sweetest place on earth." Concerned about the book he had been anticipating for decades, he hurried his publisher John Murray
to hasten publication of Worms even at the risk of not making a profit.
At a dinner with Edward Aveling
(soon the son-in-law of Karl Marx
) and other atheists, he was asked how he had turned to such an "insignificant" subject as worms, to which he replied "I have been studying their habits for forty years." As with his religious views
, the old naturalist did not see things the same way as Aveling. In Darwin's view, the "insignificant" was the foundation of much greater phenomena.
Worms are found in many places, from the forest floor to mountains, and in many locations around the world. Though they are considered terrestrial animals, they are really semi-aquatic, like other annelid
s; they die quickly in air but survive for months in water. Though inactive during the day, they sometimes come out of their burrows at night. They are eaten by thrush
es and other birds in large numbers because they lie close to the surface. They have well developed muscular, nervous, circulatory and digestive systems, the latter being quite unique. Though eyeless, they respond to the intensity and duration of light. They also slowly respond to temperature. They have no hearing, but are sensitive to vibrations. Their sense of smell is feeble, but they are able to find their preferred foods. Omnivorous animals, they swallow much earth and extract food from it. Worms live chiefly on half decayed leaves
, partially digested by a pancreatic solution
before ingestion. This extra-stomachal digestion is not unlike that which Darwin had previously described as occurring in Insectivorous Plants
. The structure and physiology of the calciferous glands of earthworms are described. Many hypotheses had been advanced for their function; Darwin believed them to be primarily for excretion
and secondarily a digestion
aid.
Thin leaves are seized with the mouth, while thick ones are dragged by creating a vacuum. Leaves and stones are used to plug up the burrow. This may deter predators, keep out water and/or keep out chilled air (the latter is Darwin's preferred function). Leaves are dragged in mostly by the tips, which is the easiest way of doing it, but when the base is narrower the worms change behaviour. They drag pine needle clusters in by the base. Petiole
s are used to plug up burrows, and for food. Worms drag experimental triangles of paper by the apex most of the time, and do not rely on trial and error
. Worms excavate burrows by consuming material or, preferably, pushing it away. They mainly consume soil
for nutrients. They are found down to six or more feet, especially in extreme conditions. Burrows are lined, which serve several functions, and terminate in a chamber lined with stones or seeds. Worms are found all over the planet, some on isolated islands; how they got there is a mystery. Darwin draws on correspondence with people from around the world such as Fritz Müller
in Brazil.
The amount of earth brought to the surface by worms can be estimated by the rate at which objects on the surface are buried and by weighing the earth brought up in a given time. Information from farmers on marl, cinders etc. sinking into the ground allowed Darwin to make calculations. He conducted a 29 year experiment on chalk at a field near his house. Objects of all sorts "work themselves downards" as farmers say. Large stones sink because worms fill up any hollows with castings, then eject them beyond the perimeter and the ground around them starts to rise. He visited Stonehenge
and found some outer stones partly buried, the turf sloping up to meet them (see figure 7). Darwin weighed castings and had friends do so in other countries. He also weighed castings per unit area per year, then worked out how thick a layer castings would make, compared with rates of sinking. Additionally, he worked out casting weight per worm per year.
Worms have preserved many ancient objects under the ground. Darwin describes an ancient Roman villa
in Abinger
, Surrey
. Worms have penetrated the concrete walls and even mortar. Similar subsidence occurred at Beaulieu Abbey
, Hampshire
, with worms penetrating gaps between the tiles. His sons Francis
and Horace
visited Chedworth Roman Villa
in Gloucestershire
, while William reported on Brading Roman Villa
, Isle of Wight
. Darwin goes into some detail on the well preserved ruins of Silchester Roman Town, Hampshire, with the help of the Rev. J. G. Joyce. Finally he discusses the case of the Viroconium Roman town ruins at Wroxeter
, Shropshire
, with the help of Dr. H. Johnson, who made observations including depth of vegetable mould. He concludes that both worms and other causes, such as dust deposition and washing down of soil, have buried such ruins.
Denudation
(removal of matter to a lower level) is caused mainly by air and water movement. Humic acid
s generated by worms disintegrate rock; their burrowing behaviour speeds this up. But as the soil layer thickens, this process is slowed down. Worms swallow hard objects (e.g. stones) to aid digestion, which causes attrition to such objects. This has geological significance, especially for the smaller particles which otherwise are eroded very slowly.
Rain
causes castings to move down an incline; Darwin worked out the weight moving a certain distance in a given time. Some also roll down, and collect in drains etc., or get blown. There is a greater effect on casting movement in the tropics, because of increased rain. The finest earth is washed away. Ledges on hillsides, formerly believed to be caused by grazing mammals, are partly due to casting accumulations. High wind
s, especially gales, are almost as effective as the slope/rain in moving castings. Crowns and furrows of formerly ploughed lands slowly vanish when under pasture
, due to worms, but more slowly when there is no incline. Fine earth is washed down from slopes, making a shallow layer. Dissolving of chalk supplies new earth.
Darwin writes in the conclusion that worms "have played a more important part in the history of the world than most persons would at first suppose." They are important for many reasons, including their role in decomposition of rocks, gradual denudation of the land, preservation of archaeological remains, and improving soil conditions for plant
growth. Despite their rudimentary sense organs, they show complex, flexible behaviour.
Worms became available in October 1881 and sold thousands of copies in its first few weeks, despite Darwin's comment to Carus that it was "a small book of little moment". Darwin received a "laughable" number of letters containing questions, observations and ideas, even "idiotic" ones. A week's holiday with Emma
in Cambridge
was to follow. Darwin died the next year on April 19, 1882.
1881 in literature
The year 1881 in literature involved some significant new books.-Events:* March 4 - A Study in Scarlet, the first Sherlock Holmes story, begins.* The first of the three-volume History of Woman Suffrage, was published by Susan B...
book
Book
A book is a set or collection of written, printed, illustrated, or blank sheets, made of hot lava, paper, parchment, or other materials, usually fastened together to hinge at one side. A single sheet within a book is called a leaf or leaflet, and each side of a leaf is called a page...
by Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
on earthworms. It was his last scientific book, and was published shortly before his death (see Darwin from Insectivorous Plants to Worms
Darwin from Insectivorous plants to Worms
The life and work of Darwin from Insectivorous Plants to Worms featured a continuation from Charles Darwin's investigations into insectivorous plants and climbing plants which he had begun before his work on Descent of Man and Emotions. Worries about family illnesses contributed to his interest...
). Exploring earthworm behavior and ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, it continued the theme common throughout his work that gradual changes over long periods of time can lead to large and sometimes surprising consequences. It was the first significant work on soil bioturbation
Bioturbation
In oceanography, limnology, pedology, geology , and archaeology, bioturbation is the displacement and mixing of sediment particles and solutes by fauna or flora . The mediators of bioturbation are typically annelid worms , bivalves In oceanography, limnology, pedology, geology (especially...
, although that term was not used by Darwin (it first appeared in the soil and geomorphic literature one hundred years later).
Paper "On the Formation of Mould"
After returning from the Beagle survey expeditionSecond voyage of HMS Beagle
The second voyage of HMS Beagle, from 27 December 1831 to 2 October 1836, was the second survey expedition of HMS Beagle, under captain Robert FitzRoy who had taken over command of the ship on its first voyage after her previous captain committed suicide...
in October 1836, Darwin was intensively occupied with further establishing his reputation as an innovative geologist
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, as well as finding suitable experts to describe his natural history
Natural history
Natural history is the scientific research of plants or animals, leaning more towards observational rather than experimental methods of study, and encompasses more research published in magazines than in academic journals. Grouped among the natural sciences, natural history is the systematic study...
collections and arranging for publication of their work as the multi-volume Zoology of the Voyage of H.M.S. Beagle
Zoology of the Voyage of H.M.S. Beagle
The Zoology of the Voyage of H.M.S. Beagle Under the Command of Captain Fitzroy, R.N., during the Years 1832 to 1836 is a 5-part book published unbound in nineteen numbers as they were ready, between February 1838 and October 1843...
. Near the outset of the voyage he had planned a book on geology, and during it extracts from his letters on geology had been privately published by his tutor John Stevens Henslow
John Stevens Henslow
John Stevens Henslow was an English clergyman, botanist and geologist. He is best remembered as friend and mentor to his pupil Charles Darwin.- Early life :...
. Darwin now published papers on "proofs of recent elevation on the coast of Chili", "deposits containing extinct Mammalia" and "coral formations". He also rewrote his journal to incorporate observations from his notebooks as the book now called The Voyage of the Beagle
The Voyage of the Beagle
The Voyage of the Beagle is a title commonly given to the book written by Charles Darwin and published in 1839 as his Journal and Remarks, bringing him considerable fame and respect...
, and began brainstorming in his notebooks about transmutation of species
Transmutation of species
Transmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another, and the term is often used to describe 19th century evolutionary ideas that preceded Charles Darwin's theory of natural selection...
.
Darwin’s health suffered from the pressure of work, and on 20 September 1837 having been urged by his doctors "knock off all work" he visited his home in Shrewsbury
Shrewsbury
Shrewsbury is the county town of Shropshire, in the West Midlands region of England. Lying on the River Severn, it is a civil parish home to some 70,000 inhabitants, and is the primary settlement and headquarters of Shropshire Council...
then went on to stay with his relatives at Maer Hall
Maer Hall
The large 17th century stone built country house and estate of Maer Hall dominates the village of Maer, Staffordshire. Its location in the district of Newcastle-under-Lyme, Staffordshire, England, is attractively rural, but fairly close to the pottery manufacturing area around Stoke-on-Trent which...
, Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...
, home of his uncle Josiah Wedgwood
Josiah Wedgwood II
Josiah Wedgwood II , the son of the English potter Josiah Wedgwood, continued his father's firm and was Member of Parliament for Stoke-upon-Trent from 1832 to 1835...
. Uncle Jos pointed out an area of ground where lime
Agricultural lime
Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil additive made from pulverized limestone or chalk. The primary active component is calcium carbonate...
and cinders spread years previously had vanished into the soil, forming layers under a top layer of loam
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...
. Jos suggested that this might have been the work of earthworm
Earthworm
Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...
s, but apparently thought that this would be of little interest to his nephew, who was working on continental scale geological problems. Actually, Charles did find it interesting and throughout his life he sustained an interest in this "unsung creature which, in its untold millions, transformed the land as the coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
polyps did the tropical sea".
He returned to London on 21 October and prepared a paper on worms forming mould. The paper on the role of earthworms in soil formation
Pedogenesis
Pedogenesis is the science and study of the processes that lead to the formation of soil ' and first explored by the Russian geologist Vasily Dokuchaev , the so called grandfather of soil science, who determined that soil formed over time as a consequence of...
was read out by Darwin at the Geological Society of London
Geological Society of London
The Geological Society of London is a learned society based in the United Kingdom with the aim of "investigating the mineral structure of the Earth"...
on 1 November 1837. This was an uncommonly mundane subject for the society, and his peers may have hoped to hear of something more grandiose, even seeing this paper as highlighting Darwin's growing idiosyncrasies. The leading geologist William Buckland
William Buckland
The Very Rev. Dr William Buckland DD FRS was an English geologist, palaeontologist and Dean of Westminster, who wrote the first full account of a fossil dinosaur, which he named Megalosaurus...
subsequently recommended Darwin's paper for publication, praising it as "a new & important theory to explain Phenomena of universal occurrence on the surface of the Earth—in fact a new Geological Power", while rightly rejecting Darwin's suggestion that chalkland could have been formed in a similar way.
The paper appeared in the Proceedings of the Geological Society of London in 1838, and was published with a woodcut
Woodcut
Woodcut—occasionally known as xylography—is a relief printing artistic technique in printmaking in which an image is carved into the surface of a block of wood, with the printing parts remaining level with the surface while the non-printing parts are removed, typically with gouges...
illustration in the Transactions of the Geological Society in 1840.
Renewed work on earthworms
From his brainstorming about transmutation towards the end of 1838, Darwin conceived of his theory of natural selectionNatural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
“by which to work”, as his “prime hobby”. His main work on the Beagle collections continued, and in 1842 he published the first of three volumes on geology, The Structure and Distribution of Coral Reefs
The Structure and Distribution of Coral Reefs
The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836, was published in 1842 as Charles Darwin's first monograph, and set out his theory of the formation of coral reefs...
. He then allowed himself to write out the first “pencil sketch” of his theory. Subsequently, in September 1842, the family moved to rural Down House
Down House
Down House is the former home of the English naturalist Charles Darwin and his family. It was in this house and garden that Darwin worked on his theories of evolution by natural selection which he had conceived in London before moving to Downe....
where he had space for experimental plant and animal breeding, and surroundings to observe nature. In December of that year he had a quantity of broken chalk spread over a part of a long established pasture field near the house, "for the sake of observing at some future period to what depth it would become buried."
In 1872 he was having disagreements with St George Mivart about The Descent of Man. Darwin cut communication with Mivart and went the less controversial direction of the lowly worm. His network of correspondents
Correspondence of Charles Darwin
The British naturalist Charles Darwin had correspondence with numerous other luminaries of his age and members of his family. These have provided many insights about the nineteenth century, from scientific exploration and travel to religious debate and discussion...
and fans responded to his interest and "earthworm anecdotes began surfacing in his mountain of mail". He had been interested in earthworms "since his first fishing days at The Mount and flirting days at Maer". Still, other work constrained him. Broken off from Descent, he had to finish his next work The Expression of the Emotions in Man and Animals
The Expression of the Emotions in Man and Animals
The Expression of the Emotions in Man and Animals is a book by Charles Darwin, published in 1872, concerning genetically determined aspects of behaviour. It was published thirteen years after On The Origin of Species and is, along with his 1871 book The Descent of Man, Darwin's main consideration...
.
Bernard Darwin
Bernard Richard Meirion Darwin CBE JP a grandson of the British naturalist Charles Darwin, was a golf writer and high-standard amateur golfer. He was inducted into the World Golf Hall of Fame.-Biography:...
on the way, he felt his writing life was nearly over, and with so much unfinished. He wanted to write on earthworms "before joining them", but also had two more plant books in mind, and a revision of Fertilisation of Orchids
Fertilisation of Orchids
Fertilisation of Orchids is a book by Charles Darwin published on 15 May 1862 under the full explanatory title On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing...
to work on. He also began an autobiographical work
The Autobiography of Charles Darwin
The Autobiography of Charles Darwin is the autobiography of the British naturalist Charles Darwin which was published in 1887, five years after his death....
intended for his family's eyes only. After turning away a request to support a controversial book on contraception (Fruits of Philosophy) - Darwin was opposed to it - he got back to work on flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s and worms. As with much of his geological and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary work, worms were a case of gradual
Gradualism
Gradualism is the belief in or the policy of advancing toward a goal by gradual, often slow stages.-Politics and society:In politics, the concept of gradualism is used to describe the belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as...
, barely noticeable changes accumulating over time into large effects. He even went on a two hour excursion to Stonehenge
Stonehenge
Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...
to see how its monoliths had been buried by earthworm castings.
He was occupied by worms at Downe
Downe
Downe is a village in the London Borough of Bromley in London, UK.Downe is south west of Orpington and south east of Charing Cross. Downe lies in a wooded valley, and much of the centre of the village is unchanged; the former village school now acts as the village hall.-Darwin:Charles Darwin...
in 1880, his work coming first. He had help from the family, even receiving soil samples from Abinger
Abinger
Abinger is a civil parish in the Mole Valley district of Surrey, England. It includes the villages of Abinger Hammer, Sutton Abinger, Abinger Common and part of Holmbury St Mary ....
's Roman ruins. He told Vladimir Kovalevsky (his Russian translator) of slow progress with his new book.
Darwin calculated that there were 53,767 earthworms recycling away per acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...
. He carried out experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s indoors, where they worked the earth inside pots in a worm-littered room. He experimented with stimuli at night: strong light would send them into their burrows ("like a rabbit" said Darwin's grandson Bernard), but heat and sound had no effect. Their food preferences were also tested, raw carrot
Carrot
The carrot is a root vegetable, usually orange in colour, though purple, red, white, and yellow varieties exist. It has a crisp texture when fresh...
s being their favourite.
Animal behaviour
Animal behaviour is the subject of:* The field of Ethology* Animal Behaviour, a scientific journal...
, from enjoying "the pleasure of eating" (based on their eagerness for certain foods) to their sexual passions
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
, "strong enough to overcome... their dread of light", even to their social feelings ("crawling over each other's bodies"). Their foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
was especially intriguing: they dragged leaves into their burrows, pulling them in the most efficient way, by their pointed end. On these semi-intelligent creatures Darwin wrote that they obtained a "notion, however rude, of the shape of an object", perhaps by feeling it out. Worms, "five or six feet" below the ground ploughed farmers fields. Darwin felt we "ought to be grateful" to these little recyclers, which he compared to "a man... born blind and deaf". He was wondering how long it would be until he would be consumed by worms himself. It would surely be his last major work; he told German translator Victor Carus
Julius Victor Carus
Julius Victor Carus was a German zoologist, comparative anatomist and entomologist.He served as curator of the Museum of Comparative Anatomy at Oxford University from 1849 to 1851, and as professor of comparative anatomy and director of the Zoological Museum at the University of Leipzig in 1853.-...
"I have little strength & feel very old".
By 1881 he was unable to summon the strength for revisions and handed Worms on to Frank
Francis Darwin
Sir Francis "Frank" Darwin, FRS , a son of the British naturalist and scientist Charles Darwin, followed his father into botany.-Biography:Francis Darwin was born in Down House, Downe, Kent in 1848...
. His health gave him troubles; he complained to his long-time friend Hooker
Joseph Dalton Hooker
Sir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was a founder of geographical botany, and Charles Darwin's closest friend...
that he looked forward to "Down graveyard as the sweetest place on earth." Concerned about the book he had been anticipating for decades, he hurried his publisher John Murray
John Murray (publisher)
John Murray is an English publisher, renowned for the authors it has published in its history, including Jane Austen, Sir Arthur Conan Doyle, Lord Byron, Charles Lyell, Johann Wolfgang von Goethe, Herman Melville, and Charles Darwin...
to hasten publication of Worms even at the risk of not making a profit.
At a dinner with Edward Aveling
Edward Aveling
Edward Bibbins Aveling was a prominent English biology instructor and popular spokesman for Darwinian evolution and atheism. He later met and moved in with Eleanor Marx, the youngest daughter of Karl Marx and became a socialist activist...
(soon the son-in-law of Karl Marx
Karl Marx
Karl Heinrich Marx was a German philosopher, economist, sociologist, historian, journalist, and revolutionary socialist. His ideas played a significant role in the development of social science and the socialist political movement...
) and other atheists, he was asked how he had turned to such an "insignificant" subject as worms, to which he replied "I have been studying their habits for forty years." As with his religious views
Charles Darwin's views on religion
Charles Darwin's views on religion have been the subject of much interest. His work which was pivotal in the development of modern biology and evolution theory played a prominent part in debates about religion and science at the time, then in the early twentieth century became a focus of the...
, the old naturalist did not see things the same way as Aveling. In Darwin's view, the "insignificant" was the foundation of much greater phenomena.
Summary
Darwin writes that he has been interested in worms for a long time and has written on the subject before, but that his ideas have been criticized by others.Worms are found in many places, from the forest floor to mountains, and in many locations around the world. Though they are considered terrestrial animals, they are really semi-aquatic, like other annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
s; they die quickly in air but survive for months in water. Though inactive during the day, they sometimes come out of their burrows at night. They are eaten by thrush
Thrush (bird)
The thrushes, family Turdidae, are a group of passerine birds that occur worldwide.-Characteristics:Thrushes are plump, soft-plumaged, small to medium-sized birds, inhabiting wooded areas, and often feed on the ground or eat small fruit. The smallest thrush may be the Forest Rock-thrush, at and...
es and other birds in large numbers because they lie close to the surface. They have well developed muscular, nervous, circulatory and digestive systems, the latter being quite unique. Though eyeless, they respond to the intensity and duration of light. They also slowly respond to temperature. They have no hearing, but are sensitive to vibrations. Their sense of smell is feeble, but they are able to find their preferred foods. Omnivorous animals, they swallow much earth and extract food from it. Worms live chiefly on half decayed leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, partially digested by a pancreatic solution
Pancreatic juice
Pancreatic juice is a liquid secreted by the pancreas, which contains a variety of enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, and amylase....
before ingestion. This extra-stomachal digestion is not unlike that which Darwin had previously described as occurring in Insectivorous Plants
Insectivorous Plants (book)
Insectivorous Plants is a book by British naturalist and evolutionary theory pioneer Charles Darwin, first published on 2 July 1875 in London....
. The structure and physiology of the calciferous glands of earthworms are described. Many hypotheses had been advanced for their function; Darwin believed them to be primarily for excretion
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
and secondarily a digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
aid.
Thin leaves are seized with the mouth, while thick ones are dragged by creating a vacuum. Leaves and stones are used to plug up the burrow. This may deter predators, keep out water and/or keep out chilled air (the latter is Darwin's preferred function). Leaves are dragged in mostly by the tips, which is the easiest way of doing it, but when the base is narrower the worms change behaviour. They drag pine needle clusters in by the base. Petiole
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
s are used to plug up burrows, and for food. Worms drag experimental triangles of paper by the apex most of the time, and do not rely on trial and error
Trial and error
Trial and error, or trial by error, is a general method of problem solving, fixing things, or for obtaining knowledge."Learning doesn't happen from failure itself but rather from analyzing the failure, making a change, and then trying again."...
. Worms excavate burrows by consuming material or, preferably, pushing it away. They mainly consume soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
for nutrients. They are found down to six or more feet, especially in extreme conditions. Burrows are lined, which serve several functions, and terminate in a chamber lined with stones or seeds. Worms are found all over the planet, some on isolated islands; how they got there is a mystery. Darwin draws on correspondence with people from around the world such as Fritz Müller
Fritz Müller
Johann Friedrich Theodor Müller , better known as Fritz Müller, and also as Müller-Desterro, was a German biologist and physician who emigrated to southern Brazil, where he lived in and near the German community of Blumenau, Santa Catarina...
in Brazil.
The amount of earth brought to the surface by worms can be estimated by the rate at which objects on the surface are buried and by weighing the earth brought up in a given time. Information from farmers on marl, cinders etc. sinking into the ground allowed Darwin to make calculations. He conducted a 29 year experiment on chalk at a field near his house. Objects of all sorts "work themselves downards" as farmers say. Large stones sink because worms fill up any hollows with castings, then eject them beyond the perimeter and the ground around them starts to rise. He visited Stonehenge
Stonehenge
Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...
and found some outer stones partly buried, the turf sloping up to meet them (see figure 7). Darwin weighed castings and had friends do so in other countries. He also weighed castings per unit area per year, then worked out how thick a layer castings would make, compared with rates of sinking. Additionally, he worked out casting weight per worm per year.
Worms have preserved many ancient objects under the ground. Darwin describes an ancient Roman villa
Roman villa
A Roman villa is a villa that was built or lived in during the Roman republic and the Roman Empire. A villa was originally a Roman country house built for the upper class...
in Abinger
Abinger
Abinger is a civil parish in the Mole Valley district of Surrey, England. It includes the villages of Abinger Hammer, Sutton Abinger, Abinger Common and part of Holmbury St Mary ....
, Surrey
Surrey
Surrey is a county in the South East of England and is one of the Home Counties. The county borders Greater London, Kent, East Sussex, West Sussex, Hampshire and Berkshire. The historic county town is Guildford. Surrey County Council sits at Kingston upon Thames, although this has been part of...
. Worms have penetrated the concrete walls and even mortar. Similar subsidence occurred at Beaulieu Abbey
Beaulieu Abbey
Beaulieu Abbey, , was a Cistercian abbey located in Hampshire, England. It was founded in 1203-1204 by King John and peopled by 30 monks sent from the abbey of Cîteaux in France, the mother house of the Cistercian order...
, Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
, with worms penetrating gaps between the tiles. His sons Francis
Francis Darwin
Sir Francis "Frank" Darwin, FRS , a son of the British naturalist and scientist Charles Darwin, followed his father into botany.-Biography:Francis Darwin was born in Down House, Downe, Kent in 1848...
and Horace
Horace Darwin
Sir Horace Darwin, KBE, FRS , a son of the English naturalist Charles Darwin, was a civil engineer.Darwin was born in Down House in 1851, the fifth son and ninth child of the British naturalist Charles Darwin and his wife Emma, the youngest of their seven children that survived to adulthood.He was...
visited Chedworth Roman Villa
Chedworth Roman Villa
Chedworth Roman Villa is a Roman villa located at Chedworth, Gloucestershire, England. It is one of the largest Roman villas in Britain.-Siting:...
in Gloucestershire
Gloucestershire
Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....
, while William reported on Brading Roman Villa
Brading Roman Villa
Brading Roman Villa was a Roman courtyard villa which has been excavated and put on public display in Brading on the Isle of Wight.-1879 - present day:...
, Isle of Wight
Isle of Wight
The Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...
. Darwin goes into some detail on the well preserved ruins of Silchester Roman Town, Hampshire, with the help of the Rev. J. G. Joyce. Finally he discusses the case of the Viroconium Roman town ruins at Wroxeter
Wroxeter
Wroxeter is a village in Shropshire, England. It forms part of the civil parish of Wroxeter and Uppington and is located in the Severn Valley about south-east of Shrewsbury.-History:...
, Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
, with the help of Dr. H. Johnson, who made observations including depth of vegetable mould. He concludes that both worms and other causes, such as dust deposition and washing down of soil, have buried such ruins.
Denudation
Denudation
In geology, denudation is the long-term sum of processes that cause the wearing away of the earth’s surface leading to a reduction in elevation and relief of landforms and landscapes...
(removal of matter to a lower level) is caused mainly by air and water movement. Humic acid
Humic acid
Humic acid is a principal component of humic substances, which are the major organic constituents of soil , peat, coal, many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter...
s generated by worms disintegrate rock; their burrowing behaviour speeds this up. But as the soil layer thickens, this process is slowed down. Worms swallow hard objects (e.g. stones) to aid digestion, which causes attrition to such objects. This has geological significance, especially for the smaller particles which otherwise are eroded very slowly.
Rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
causes castings to move down an incline; Darwin worked out the weight moving a certain distance in a given time. Some also roll down, and collect in drains etc., or get blown. There is a greater effect on casting movement in the tropics, because of increased rain. The finest earth is washed away. Ledges on hillsides, formerly believed to be caused by grazing mammals, are partly due to casting accumulations. High wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s, especially gales, are almost as effective as the slope/rain in moving castings. Crowns and furrows of formerly ploughed lands slowly vanish when under pasture
Pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...
, due to worms, but more slowly when there is no incline. Fine earth is washed down from slopes, making a shallow layer. Dissolving of chalk supplies new earth.
Darwin writes in the conclusion that worms "have played a more important part in the history of the world than most persons would at first suppose." They are important for many reasons, including their role in decomposition of rocks, gradual denudation of the land, preservation of archaeological remains, and improving soil conditions for plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
growth. Despite their rudimentary sense organs, they show complex, flexible behaviour.
Reception
Emma Darwin
Emma Darwin was the wife and first cousin of Charles Darwin, the English naturalist, scientist and author of On the Origin of Species...
in Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...
was to follow. Darwin died the next year on April 19, 1882.
Further reading
- "Down among the Worms", chapter 42 in