The formation of the soil through the action of worms
The formation of the soil through the action of worms (in the English original: The Formation of Vegetable Mold through the Action of Worms, with Observations on their Habits , sometimes used short form: Worms ) is the title of a work by Charles Darwin , the first edition on 10 Published October 1881. A year before his death, Darwin concluded with this book his decades-long studies of the interrelationships between earthworms and soil conditions and of the behavior of these animals.
At the beginning of the 19th century earthworms were considered pests - especially outside of agricultural science . Darwin's precise observations of their way of life as well as his experiments on their hearing , their sensitivity to light , their perception of cold and warmth and the activity of their reflexes led to the fact that the knowledge about the usefulness of earthworms for agriculture spread rapidly and also gained acceptance outside of specialist circles.
Evidence from different continents Darwin used the example of Ecology first of earthworms also the importance of living beings for bottoming on.
History of origin
From December 1831 to October 1836 Charles Darwin took part in a survey of the HMS Beagle , which had taken him around the globe. Immediately after his return he began to organize the materials, manuscripts and notes he had collected during these five years and to prepare the planned publications, the first of which appeared in February 1838 under the title The Zoology of the Voyage of HMS Beagle . The aftermath of the long sea voyage and the intensive work on the manuscripts affected Darwin's health so much that his doctors advised him in 1837 to stop all work for a few weeks and spend the summer in the country. Darwin spent these holiday weeks with his uncle Josiah Wedgwood II in Maer , Staffordshire .
During this summer vacation , his uncle reported an observation that he had made shortly before in several of his meadows. Francis Darwin , Darwin's third son, recalled in 1887 that his father had never denied the inspiration for his earthworm study: “He owed his uncle Josiah Wedgwood for pointing out that worms, by bringing earth to the surface in their solution , undermining every object lying on the surface. ”A few weeks after his departure from Maer, on November 1, 1837, Darwin read a short treatise On the formation of mold before the Geological Society of London ("About the formation of the soil") ...
"[...] in which it was shown that small fragments of burnt marl , slag, etc., which had been scattered thickly over the surface of several meadows, after a few years lay a few inches below the lawn , but still one Forming a layer were found. This apparent sinking of superficial objects is, as Mr. Wedgwood of Maer Hall, Staffordshire, first voiced as a conjecture against me, a consequence of the great quantity of fine earth which worms continually bring to the surface in the form of their cylindrical castings . Sooner or later these castings will be spread out and cover every object left on the surface. I was hereby led to the conclusion that all of the soil throughout the country has passed through the digestive canals of worms many times, and will pass through many more times. "
Darwin's lecture was published in 1838 in the abstract of an unknown author in the Proceedings of the Geological Society of London and again in 1840 by Darwin himself - in a revised and supplemented version - in the Transactions of the Geological Society . A misprint in this second publication finally led Darwin to write a short notice in Gardeners' Chronicle and Agricultural Gazette in 1844 , this time under the title On the Origin of Mold .
It was not until ten years after Charles Darwin had completed his main work, The Origin of Species , and began work on Human Descent and Sexual Selection , that from 1869 onwards he dealt again with the importance of earthworms for the quality of the soil. It was triggered by a criticism of his short message from 1844 in the Gardeners' Chronicle :
“In 1869, Mr. Fish rejected my conclusions about the role worms played in the formation of the soil, simply because of their perceived inability to do such work. He remarks that 'in view of their weakness and their small size, the work which they are supposed to have done according to that account would be quite astonishing'. […] Although these various objections did not seem to have any importance to me, I decided to make more observations of the same kind as those already published […]. "
From three letters from Darwin's niece, Lucy Wedgwood, it emerges that, at the request of her uncle, she observed the activities of earthworms as early as May 1870, which she apparently kept in vessels; However, it was only from the winter of 1870/71 onwards that there was evidence of an accumulation of Darwin's notes on this subject.
In the following ten years Darwin compiled all available literature on earthworms, asked for specimens from remote parts of the world or at least precise descriptions of the droppings, and carried out numerous experiments of his own. The manuscript was finally completed at the end of March 1881; the publication of the book was delayed until October 1881, because Darwin's English publisher wanted it to appear simultaneously in England and the USA .
content
The behavior of earthworms
Even before the completion of his behavioral biological work published in 1872, The Expression of Emotional Movements in Humans and Animals , Darwin had begun to deal specifically with the excretions of earthworms on the one hand, but also to study their behavior in general on the other .
In the introduction to the formation of the soil , Darwin wrote:
“Since I was induced to keep worms in pots filled with earth in my study for many months, I began to be interested in them and wished to find out to what extent they acted consciously and how much intellectual faculties they developed. I was all the more eager to learn about this point, since, so far as I know, few observations of this kind have been made in animals which are on such a low level of organization and so poorly equipped with sensory organs as earthworms. "
In fact, Darwin dedicated almost 70 of the 180 or so pages of text to the “worms' way of life”. He described their physique and the nature of the places they inhabited and showed that they are predominantly nocturnal, can crawl long distances and can live under water. He described in detail experiments that show that earthworms - which have no eyes - can still differentiate between light and darkness and - according to his assumption, thanks to existing reflections - quickly retreat into their tubes when they are brightly lit. Darwin tested her sensitivity to heat and cold, to vibrations in the ground and in the air:
“Worms have no sense of hearing. They took not the slightest notice of the piercing tones of a metal pipe, which were repeatedly produced near them; just as little of the deepest and loudest notes of a bassoon . They were indifferent to shouting, if only care was taken that the breath did not hit them. If they were placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly still. "
On the other hand, Darwin confirmed, changes in pressure in the soil can be perceived by earthworms:
“Although they are insensitive to vibrations in the air that are audible to us, they are extremely sensitive to vibrations in any solid body. […] It has often been stated that if the ground were struck, or otherwise made to tremble, the worms then believed that they were being pursued by a mole , and therefore abandoned their burrows. I hit the ground in many places where worms were extremely numerous, but not one came out. "
Darwin also tested the earthworms' sense of smell , their food preferences, prepared their digestive system and analyzed its glands. Over several printed pages he then described experiments that his son Francis carried out: How do earthworms pull leaves and other potential food, but also small paper triangles and other objects into their tubes at night? As some of these objects only disappeared into the tubes after repeated attempts at pulling them, Darwin came to the conclusion:
"When we consider these different cases, we can hardly avoid the conclusion that worms display a certain degree of intelligence in the way they plug their tubes."
Finally, Darwin described the procedure of earthworms when they hollow out their burrows (this happens, according to his observations, by pushing the earth away on all sides or by devouring it) and compared the - quite similar - appearance of the dung piles of English, French, Indian and Ceylonese Worms. From the foreign heaps of excrement sent to him, Darwin generalized his own observations made in England, and concluded that "the worms are engaged in bringing fine earth to the surface in most or all parts of the earth and under the most varied climates" .
Soil studies
A Sward
B Arable soil without any stones
C Arable earth with fragments of burnt marl, coal slag and quartz pebbles
D Sub-soil of dark, peaty sandy soil with pebbles
After the behavioral analyzes, Darwin devoted himself to “the more immediate subject” of his work, namely “the amount of earth that is brought up by the worms from below the surface and later spread more or less completely by the rain and wind.” He first described in detail the event that his uncle had explained to him decades earlier: Around 1827, coarsely ground lime was spread thickly over a field near Maer Hall, which ten years later could be detected at a depth of three inches (eight centimeters) . On a second piece of field, marl and slag were sown in 1822 , which in 1837 was stored three to four inches (eight to ten centimeters) below the surface.
After further examples, Darwin finally describes an experiment that lasted - near his house - from December 1842 to November 1871: Within 29 years, pieces of chalk poured out reached a depth of seven inches (corresponds to about 20 centimeters), which is a throw of earth by earthworms of 0.22 inches per year means (around five millimeters per year). After considering how quickly large stones lying on the surface - such as those from Stonehenge - can sink in, Darwin tries to relate the mass of the earth moving over time to the number of earthworms living in the ground. With reference to Victor Hensen, Darwin wrote that one could assume 133,000 living earthworms per hectare , which corresponds to about 133 kilograms of earthworm biomass .
The aim of Darwin's calculations was to prove that “the effects of a constantly recurring cause” add up and therefore even small causes (read: small worms), if they are numerous and given enough time for them, produce large effects can.
Considerations on archeology and ecology
On the basis of the examples of sunken fertilizer lime in English meadows described to him, Darwin was able to estimate how deep stones could get into the ground within 20 to 30 years. Using archaeological excavation sites as an example, he also tried to estimate the share that worms had in "digging in" old buildings and antique objects:
“Archaeologists probably don't know how much they owe worms for the preservation of many ancient objects. If coins, golden ornaments, stone tools, etc. fall on the surface of the ground, they will be unmistakably buried in the castings of worms in a few years and will thus be kept safe until the country is overturned again in some later period. "
Darwin used the excavation of a Roman villa rustica , the floor and remains of the wall 13 to 15 inches (= around 40 cm) below the surface, to observe on the excavation site whether earthworms can penetrate the floor made of cement and mosaic tiles. Darwin initially suspected that the remains of the villa rustica had been covered by blown earth over the centuries, but was then able to observe that earthworm droppings were also secreted between the mosaic panels night after night. From the end of August to mid-October 1877, Darwin therefore had the number of earthworm droppings and tubes recorded on a previously cleaned area and an inspection carried out three years later. In this way, he was able to prove that earthworms - at least in the temperate climate of England - are almost always active, therefore constantly bringing earth up and, due to the occasional collapse of their tubes, can cause even larger, contiguous areas to sink in almost uniformly.
Examples examined by Darwin's son William include Beaulieu Abbey , where the floor of the destroyed nave was ten to eleven inches deep in 1872. William not only dug holes in the lawn to measure the depth himself, but also collected the earthworm droppings that were over one of the holes - so that it could be estimated that “the accumulation over a year on a square yard [= around 0.84 square meters] should be 1.68 pounds ”. Darwin finally came to the conclusion that
“That the earthworms have played a considerable part in burying and hiding several Roman and other ancient structures in England; but no doubt the washing of earth from the neighboring higher properties and the deposition of dust have greatly helped the work of concealment. "
This is followed by a longer excursus on the decomposition of crystalline rock due to the effects of air, water, temperature changes and other causes. This is followed by a description of the neutralizing effect of those substances produced by earthworms, which they secrete from calciferous glands and allow organic acids in the humus to act. From this, Darwin deduced that earthworms are at least indirectly involved in the chemical decomposition of rocks. Furthermore, through their gizzards, they are directly involved in the crushing of sand grain-sized particles. On the other hand, their tunnels were used to absorb rainwater, which reduces the erosion of soil on slopes. The corridors also served to ventilate the floor:
“They let the air go deep into the ground. They also greatly facilitate the penetration of the roots of moderate size; and these will be nourished by the humus with which the worm-burrows are lined. Many seeds owe their germination to the fact that they were covered with worm castings. "
Otto Graff confirmed this information by Darwin in the early 1970s in field experiments at the Federal Research Center for Agriculture .
Darwin concluded his remarks on the earthworm by saying:
“It is marvelous, I suppose, when we consider that the whole mass of superficial humus has passed through the bodies of earthworms, and will pass through them again every few years. The plow is one of the very oldest and most valuable human inventions; but long before it existed the land was regularly plowed by earthworms and is still being plowed all the time. One can well doubt whether there are many other animals which have played such an important role in the history of the earth as these lowly organized creatures. "
Effect in the 19th century
Within a month of its publication, 3500 copies of the English first edition had been sold, three years later sales were 8500 copies. The book was translated twice into Russian, French, Italian and German as early as 1882. The only translation into German so far was published by E. Schweizerbart'schen Verlagsbuchhandlung, taken care of by the zoologist Julius Victor Carus , who had previously translated, among other things, Darwin's Origin of Species and The Expression of the Emotions in Man and Animals ; The second (and so far last) German edition followed in 1899 by the same publisher.
Darwin had received 100 free copies of his book and sent many of them to friends and colleagues in October 1881, who commented on the book "mostly enthusiastically or at least approvingly", whereas the reviewers of some popular magazines - for example in the USA and Belgium - rejected Darwin's representations, since earthworms are pests of plants. In Germany and Austria, however, Darwin's book received positive reviews in numerous journals . A major contributor to this was that the physiologist Victor Hensen, who teaches at the University of Kiel , experimented parallel to Darwin On the Relationship of the Earthworm to the Reclamation of Soil - the title of a lecture by Hensen - and in this way prepared the field for Darwin's theses. In June 1881, for example, Louis Pasteur also argued that pathogens from deeper layers of the earth can reach the surface in the droppings of earthworms: At that time it was common to collect cattle , sheep and horses that had died from anthrax pathogens ( Bacillus anthracis ) on a farm or field Bury meadow area. High concentrations of anthrax pathogens had been discovered in the earthworms' excrement balls above these carcasses , which were detectably ingested by grazing animals and led to further infections. A year later, Robert Koch also discussed this form of infection in his publication "About Anthrax Vaccination".
The Viennese press recommended the book to its readers as early as November 9, 1881, because Darwin wrote it “with the simplicity and clarity” that we know from him; it is "free of technical terminology" and therefore a "highly captivating book" - "captivating like a fairy tale". A two-part review in the Illustrirten Zeitung began in December 1881, for example, with the statement that “there is conclusive evidence that the common and often so neglected earthworms play a very important role in the household of nature.” And in early 1882 it said in a detailed discussion in The Present on earthworms, "since October 10, the first day of publication of Darwin's latest work, people have occupied themselves with them by whom they were previously hardly regarded, and all the newspapers and journals know of their great deeds." At the same point, reference was made to the parallels to Darwin's study of the origin of species ("small causes, large effects") and it was noted that Darwin's thesis of the creation of fertile soil through the activity of worms "through direct experiments by V. Hensen" has been confirmed. The review in The Present concluded as follows:
“Thousands of otherwise keen enough eyes have previously perceived the activity of earthworms without making such conclusions as they now appear to us to be fairly obvious. It is always reserved for the in-depth look of a man who knows how to appreciate even the smallest effects, to stimulate such problems and thereby to move beings of the lowest and most despised kind into the center of interest. "
Despite many positive comments: Darwin's theses did not remain undisputed in German-speaking countries either. Above all, the German agricultural scientist Ewald Wollny - he was considered the most important soil scientist of his time - expressed himself in 1882 in the journal he published, rejecting research in the field of agricultural physics , and also considered Hensen's experiments to be flawed. Wollny, "a capacity of scientific agriculture at the time" tried in the following years to experimentally secure his position that earthworms were pests against Darwin and Hensen. Wollny reported in 1890 about his experiments carried out in 1883/84 and from 1888 to 1890. In the introduction he wrote:
“Contrary to the expectations held by the speaker up until then, the preliminary examinations already delivered a surprising result in favor of the worms' effects. […] In not a single experiment had the plants suffered any damage from the worms. "
With Wollny's “conversion” - wrote Otto Graff in his review of “the earthworm question in the 18th and 19th centuries” - “the earthworm question, at least in Germany, was decided in favor of the predominant usefulness of these animals through science.” Wollny's experiments had proven, among other things that earthworms can bring about significant yield improvements in a wide variety of crops. The quasi-official recognition of earthworms as beneficial agricultural animals followed in 1892, when Victor Hensen was invited by Albert Schultz-Lupitz to give a lecture on earthworms at the winter meeting of the German Agricultural Society .
Appreciation in the 20th and 21st centuries
In 1936 Darwin was honored as one of the founding fathers of soil science by its editor Arseni Arsenjewitsch Jarilow (1868-1947) because of his book in the first specialist journal for soil science , which had existed since 1899 - the Potschwowedenije (then referred to as Pochvovedenie ) , which appeared in Russia . The Russian soil scientist Merkuri Giljarow (1912–1985) also described Darwin's book as a root of invertebrates - ethology .
Between 1972 and 1979, Dutch researchers collected data on the incidence of earthworms on grassland in a newly developed polder area in East Flevoland . They concluded that Darwin had estimated earthworm biomass quite low. According to the Dutch researchers, there are 300 to 900 earthworms per square meter (on average 500) living under undisturbed grasslands, the biomass of which is 2500 kg per hectare .
In 1979, a study was published in Great Britain which - inspired by Darwin's observations on the sinking of stones in the ground - demonstrated a comparable occurrence in grass seeds. Both under laboratory conditions and in the field, seeds applied superficially got underground more often when earthworms were native to them. Since superficial seeds are more frequently eaten by birds and other animals, “burrowing” the seeds results in an increased number of seedlings. From this it was deduced that "the effects of earthworms on the seeds are clearly important for the population dynamics of plants."
In 2008, the biologist Kenneth Catania confirmed the hypothesis, quoted by Darwin but not extensively researched experimentally, that earthworms react to the burial noises of nearby moles by crawling out of their tunnels to the surface: the earthworms of the species Diplocardia, which are endemic to the USA mississippiensis could be induced to leave their tunnels by the playing of recorded burial noises of the East American mole . Catania suspected that the earthworms avoid their predators in this way, since they hardly look for food on the surface of the earth.
In a review from 2004, the authors had already pointed out that following Wollny's study of 1890, research into the relationship between earthworms and soil conditions was initially carried out almost exclusively in Europe. It was not until the 1930s that Chinese and US researchers, and from the 1950s also Indian and New Zealand researchers, took up this topic. Since then, thousands of publications have appeared that have confirmed many of Darwin's conclusions - especially his observations on the influence of earthworms on the terrestrial portion of the biosphere :
“Today it is well recognized that earthworms are important agents for the maintenance of 'healthy soils', and that they act as indicators of environmental quality. The resurgence of interest in organic farming and 'biological agriculture' (in which earthworms play a more important role influencing soil fertility) in recent years has brought Darwin's book and earthworms back into the limelight. "
“Today it is generally accepted that earthworms are important helpers in maintaining 'healthy soils' and that they serve as indicators of environmental quality. The resurgence of interest in organic farming and 'organic farming' (where earthworms play a more important role because they affect soil fertility) in recent years has brought Darwin's book and the earthworms back into the spotlight. "
In 2012, researchers at the Johann Heinrich von Thünen Institute described the importance of earthworms as follows:
“The activity of earthworms helps to improve the root growth of plants, to control the supply of nutrients, to aerate the soil, to neutralize the pH value of the soil, to increase the water-holding capacity of the soil and to improve the soil structure. Against the background of these achievements, maintaining their abundance and diversity is of great benefit to the fertility of arable soils. "
literature
First editions
- Charles Darwin: The formation of vegetable mold, through the action of worms, with observations on their habits. London: John Murray, 1881; Digitized version
- Charles Darwin: The formation of the soil by the action of worms. Translated from the English by J. Victor Carus . Stuttgart: Swiss beard, 1882; to be found digitized at darwin-online.org.uk (exact photographic reproduction) and full text (scan converted to PDF; 2.1 MB)
Secondary literature
- John E. Satchell (Ed.): Earthworm Ecology. From Darwin to Vermiculture. London, New York: Chapman and Hall, 1983; ISBN 0-412-24310-5 .
- Otto Graff : The earthworm question in the 18th and 19th centuries and the importance of Victor Hensen. In: Journal of Agricultural History and Agricultural Sociology. Volume 27, issue 2, October 1979.
- Ulrich Kutschera and John Malcolm Elliott: Charles Darwin's Observations on the Behavior of Earthworms and the Evolutionary History of a Giant Endemic Species from Germany, Lumbricus badensis (Oligochaeta: Lumbricidae). In: Applied and Environmental Soil Science. Volume 2010, Article ID 8230472, 2010, pp. 1–11, doi: 10.1155 / 2010/823047 .
Web links
- Darwin's earthworms : audio file from hr2-kultur on the Hessian education server
Individual evidence
- ↑ hypersoil.uni-muenster.de : Significance of earthworms in the past - In the 1835 edition of the “Encyclopedy of Gardening” under the heading “earthworms” on page 699 there is the following quote: “Earthworms, which in large numbers are present cannot be counted among the harmful animals, although farmers and gardeners harbor prejudices against them. ”In the 1st edition of 1822, however, it was advised at the same point to collect them from the field after digging up.
- ↑ According to the editor, JE Satchell, in his foreword to the anthology: Earthworm Ecology. From Darwin to Vermiculture. London, New York: Chapman and Hall, 1983
- ^ Otto Graff : Darwin on earthworms - the contemporary background and what the critics thought. In: JE Satchell (Ed.): Earthworm Ecology ..., p. 5
- ^ Francis Darwin : The Life and Letters of Charles Darwin. Murray, London. Translated from Otto Graff, Darwin on earthworms…, in: JE Satchell (Ed.): Earthworm Ecology…, p. 5
-
^ On the formation of mold. In: Proceedings of the Geological Society of London 2, 1838, pp. 574-576, full text ;
On the formation of mold. Transactions of the Geological Society (Ser. 2) 5 (2), 1840, pp. 505-509, full text - ^ On the origin of mold. In: Gardeners' Chronicle No. 14 of April 6, 1844, p. 218, facsimile (PDF) ( Memento of May 16, 2012 in the Internet Archive ) and full text
- ↑ Gardeners' Chronicle, April 17, 1869, p. 418
- ↑ Otto Graff drew attention to this in 1983, after reviewing the original documents left by Darwin, who had been studying the influence of earthworms on the condition of agricultural land at the Federal Research Center for Agriculture in Braunschweig since the early 1950s and was also a professor at the University of Gießen held. In: Darwin on earthworms ..., in: JE Satchell (Ed.): Earthworm Ecology ..., p. 10
- ↑ As early as 1776, the English country pastor Gilbert White (1720–1793), who was well versed in natural history, noticed that earthworms were "great promoters of vegetation" because they loosened the soil and their excrement was "a fine manure for grain and grass". - G. White: The Natural History and Antiquitiy os Selborne. London, 1789, p. 216 f. (= Letter XXXV of May 20, 1776)
- ↑ Darwin, Ackererde, p. 72
- ↑ Darwin, Ackererde, p. 73
- ↑ Darwin, Ackererde, p. 110
- ↑ C. Feller et al .: Darwin et le biofonctionnement des sols. In: Études de Gestion des Sols , Volume 7 (4), 2000, pp. 395–402, full text (PDF; 31 kB) ( Memento from October 15, 2016)
- ↑ Under the title: Role des vers de terre dans la formation de la terre vegetale
- ↑ Delivery status according to the publisher's directory
- ↑ Otto Graff: Darwin on earthworms ..., in: JE Satchell (Ed.): Earthworm Ecology ..., p. 13
- ^ Louis Pasteur : Sur les virus-vaccins de choléra des poules et du charbon. In: Louis Pasteur Vallery-Radot (ed.): Oeuvres de Pasteur Réunies , Volume VI, Masson et Cie, Paris 1933, p. 367. Reprinted from: Comptes rendus des travaux du Congrès international des directeurs des stations agronomiques, session de Versailles , Berger-Levrault et Cie, June 1881, pp. 151-162.
-
↑ Robert Koch : About the anthrax vaccination. Verlag von Theodor Fischer, Kassel and Berlin 1882, pp. 12–13
See also: Bernhard Möllers: Robert Koch: Personality and Lifetime Work 1843–1910. Schmorl & von Seefeld Nachf., Hannover 1950, pp. 464-465 - ↑ Darwin on earth worms. In: Die Presse of November 9, 1881, full text
- ↑ Otto Zacharias: Darwin's newest researches on the activity of earthworms. In: Illustrirte Zeitung , No. 2005 of December 3, 1881, p. 495 and No. 2006 of December 10, 1881, p. 523; Full text
- ^ Carus Sterne (= Ernst Ludwig Krause): The role of earthworms in the history of the earth. In: Die Gegenwart , No. 6, February 1882, pp. 84–86, full text
- ↑ The review of Darwin's Ackererde appeared in “Research in the field of agricultural physics”, Volume 5, Heidelberg 1882, pp. 50–55; the criticism of Hensen in "Research in the field of agricultural physics", Volume 5, Heidelberg 1882, pp. 423-4251
- ↑ Otto Graff: The earthworm question in the 18th and 19th centuries and the importance of Victor Hensen. In: Journal of Agricultural History and Agricultural Sociology , Volume 27, Issue 2, October 1979, p. 240
- ↑ Studies on the influence of the activity of earthworms on the fertility of the topsoil. In: Research in the field of agricultural physics , Volume 13, 1890, pp. 381-395
- ↑ Source: Information board in the Natural History Museum Vienna for the replica of the experiment shown here.
- ↑ AA Yarilov: C. Darviin - osnovopoloshnik nauki o pochve. (Charles Darwin - The founder of soil science). In: Potschwowedenije , Volume 4, 1936, pp. 17-23
- ^ KE Lee: In memoriam Mercurii Sergeivich Ghilarov 1912–1985. In: Biology and Fertility of Soils , Volume 3, No. 1-2, 1987, pp. 1 f., Doi : 10.1007 / BF00260570
- ↑ Mercurii Sergeivich Ghilarov: Darwin's Formation of Vegetable Mold - its philosophical basis. In: JE Satchell (Ed.): Earthworm Ecology ..., p. 4
- ↑ M. Hoogerkamp et al .: Effect of earthworm on grassland on recently reclaimed polder soils in the Netherlands. In: JE Satchell (Ed.): Earthworm Ecology ..., p. 85
- ^ JD Grant: The activities of earthworms and the fates of seeds. In: JE Satchell (Ed.): Earthworm Ecology ..., p. 107 ff.
- ↑ Kenneth C. Catania: Worm Grunting, Fiddling, and Charming - Humans Unknowingly Mimic a Predator to Harvest Bait. In: PLoS ONE 3 (10): e3472, doi : 10.1371 / journal.pone.0003472
- ↑ Kenneth Catania: Mole alarm à la Darwin. In: Spectrum of Science. Issue 2, 2011, pp. 30–33, Spektrum.de: Article excerpt and link to a video
- ^ GG Brown et al .: With Darwin, earthworms turn intelligent and become human friends. In: Pedobiologia , Volume 47, No. 5-6, 2004, pp. 924-933, doi : 10.1078 / 0031-4056-00282
- ↑ With Darwin, earthworms turn intelligent… - Monika Joschko & Otto Graff argued similarly in 1999: Die Heinzelmännchen des Boden. "Biological tillage" by earthworms. In: Landwirtschaft ohne Pflug (4), 1999, pp. 10-12
- ↑ Christine van Capelle et al .: Earthworm and Co. - indispensable helpers in agriculture. In: Senate of the Federal Research Institutes in the business area of the Federal Ministry for Food, Agriculture and Consumer Protection (Ed.): Research report . Food - Agriculture - Consumer Protection. Issue No. 45 (edition 1/2012), p. 33
