The Formation of Vegetable Mould
Through the Action of Worms
with Observations on their Habits

by Charles Darwin

John Murray, London, 1881
Faber and Faber, London, 1945

with an Introduction by
Sir Albert Howard


Introduction   Original Introduction by Charles Darwin
Introduction   by Sir Albert Howard
Chapter 1   Habits of Worms

Nature of the sites inhabited--Can live long under water--Nocturnal--Wander about at night--Often lie close to the mouths of their burrows, and are thus destroyed in large numbers by birds--Structure--Do not possess eyes, but can distinguish between light and darkness--Retreat rapidly when brightly illuminated, not by a reflex action--Power of attention--Sensitive to heat and cold--Completely deaf--Sensitive to vibrations and to touch--Feeble power of smell--Taste--Mental qualities--Nature of food--Omnivorous--Digestion--Leaves before being swallowed, moistened with a fluid of the nature of the pancreatic secretion--Extra-stomachal digestion--Calciferous glands, structure of--Calcareous concretions formed in the anterior pair of glands--The calcareous matter primarily an excretion, but secondarily serves to neutralise the acids generated during the digestive process.

Chapter 2   Habits of Worms – continued

Manner in which worms seize objects--Their power of suction--The instinct of plugging up the mouths of their burrows--Stones piled over the burrows--The advantages thus gained--Intelligence shown by worms in their manner of plugging up their burrows--Various kinds of leaves and other objects thus used--Triangles of paper--Summary of reasons for believing that worms exhibit some intelligence--Means by which they excavate their burrows, by pushing away the earth and swallowing it--Earth also swallowed for the nutritious matter which it contains--Depth to which worms burrow, and the construction of their burrows--Burrows lined with castings, and in the upper part with leaves--The lowest part paved with little stones or seeds--Manner in which the castings are ejected--The collapse of old burrows--Distribution of worms--Tower-like castings in Bengal--Gigantic castings on the Nilgiri Mountains--Castings ejected in all countries.

Chapter 3   The Amount of Fine Earth Brought Up by Worms to the Surface

Rate at which various objects strewed on the surface of grass-fields are covered up by the castings of worms--The burial of a paved path--The slow subsidence of great stones left on the surface--The number of worms which live within a given space--The weight of earth ejected from a burrow, and from all the burrows within a given space--The thickness of the layer of mould which the castings on a given space would form within a given time if uniformly spread out--The slow rate at which mould can increase to a great thickness--Conclusion.

Chapter 4   The Part which Worms Have Played in the Burial of Ancient Buildings

The accumulation of rubbish on the sites of great cities independent of the action of worms--The burial of a Roman villa at Abinger--The floors and walls penetrated by worms--Subsidence of a modern pavement--The buried pavement at Beaulieu Abbey--Roman villas at Chedworth and Brading--The remains of the Roman town at Silchester--The nature of the debris by which the remains are covered--The penetration of the tesselated floors and walls by worms--Subsidence of the floors--Thickness of the mould--The old Roman city of Wroxeter--Thickness of the mould--Depth of the foundations of some of the Buildings--Conclusion.

Chapter 5   The Action of Worms in the Denudation of the Land

Evidence of the amount of denudation which the land has undergone--Sub-aerial denudation--The deposition of dust--Vegetable mould, its dark colour and fine texture largely due to the action of worms--The disintegration of rocks by the humus-acids --Similar acids apparently generated within the bodies of worms--The action of these acids facilitated by the continued movement of the particles of earth--A thick bed of mould checks the disintegration of the underlying soil and rocks. Particles of stone worn or triturated in the gizzards of worms--Swallowed stones serve as mill-stones--The levigated state of the castings--Fragments of brick in the castings over ancient buildings well rounded. The triturating power of worms not quite insignificant under a geological point of view.

Chapter 6   The Denudation of the Land – continued

Denudation aided by recently ejected castings flowing down inclined grass-covered surfaces--The amount of earth which annually flows downwards--The effect of tropical rain on worm castings--The finest particles of earth washed completely away from castings--The disintegration of dried castings into pellets, and their rolling down inclined surfaces--The formation of little ledges on hill-sides, in part due to the accumulation of disintegrated castings--Castings blown to leeward over level land--An attempt to estimate the amount thus blown--The degradation of ancient encampments and tumuli--The preservation of the crowns and furrows on land anciently ploughed--The formation and amount of mould over the Chalk formation.

Chapter 7   Conclusion

Summary of the part which worms have played in the history of the world--Their aid in the disintegration of rocks--In the denudation of the land--In the preservation of ancient remains--In the preparation of the soil for the growth of plants--Mental powers of worms--Conclusion.



The share which worms have taken in the formation of the layer of vegetable mould, which covers the whole surface of the land in every moderately humid country, is the subject of the present volume. This mould is generally of a blackish colour and a few inches in thickness. In different districts it differs but little in appearance, although it may rest on various subsoils. The uniform fineness of the particles of which it is composed is one of its chief characteristic features; and this may be well observed in any gravelly country, where a recently-ploughed field immediately adjoins one which has long remained undisturbed for pasture, and where the vegetable mould is exposed on the sides of a ditch or hole. The subject may appear an insignificant one, but we shall see that it possesses some interest; and the maxim "de minimis non curat lex," does not apply to science. Even Elie de Beaumont, who generally undervalues small agencies and their accumulated effects, remarks: {1} "La couche tres-mince de la terre vegetale est un monument d'une haute antiquite, et, par le fait de sa permanence, un objet digne d'occuper le geologue, et capable de lui fournir des remarques interessantes." Although the superficial layer of vegetable mould as a whole no doubt is of the highest antiquity, yet in regard to its permanence, we shall hereafter see reason to believe that its component particles are in most cases removed at not a very slow rate, and are replaced by others due to the disintegration of the underlying materials.

As I was led to keep in my study during many months worms in pots filled with earth, I became interested in them, and wished to learn how far they acted consciously, and how much mental power they displayed. I was the more desirous to learn something on this head, as few observations of this kind have been made, as far as I know, on animals so low in the scale of organization and so poorly provided with sense-organs, as are earth-worms.

In the year 1837, a short paper was read by me before the Geological Society of London, {2} "On the Formation of Mould," in which it was shown that small fragments of burnt marl, cinders, etc., which had been thickly strewed over the surface of several meadows, were found after a few years lying at the depth of some inches beneath the turf, but still forming a layer. This apparent sinking of superficial bodies is due, as was first suggested to me by Mr. Wedgwood of Maer Hall in Staffordshire, to the large quantity of fine earth continually brought up to the surface by worms in the form of castings. These castings are sooner or later spread out and cover up any object left on the surface. I was thus led to conclude that all the vegetable mould over the whole country has passed many times through, and will again pass many times through, the intestinal canals of worms. Hence the term "animal mould" would be in some respects more appropriate than that commonly used of "vegetable mould."

Ten years after the publication of my paper, M. D'Archiac, evidently influenced by the doctrines of Elie de Beaumont, wrote about my "singuliere theorie," and objected that it could apply only to "les prairies basses et humides;" and that "les terres labourees, les bois, les prairies elevees, n'apportent aucune preuve a l'appui de cette maniere de voir." {3} But M. D'Archiac must have thus argued from inner consciousness and not from observation, for worms abound to an extraordinary degree in kitchen gardens where the soil is continually worked, though in such loose soil they generally deposit their castings in any open cavities or within their old burrows instead of on the surface. Hensen estimates that there are about twice as many worms in gardens as in corn-fields. {4} With respect to "prairies elevees," I do not know how it may be in France, but nowhere in England have I seen the ground so thickly covered with castings as on commons, at a height of several hundred feet above the sea. In woods again, if the loose leaves in autumn are removed, the whole surface will be found strewed with castings. Dr. King, the superintendent of the Botanic Garden in Calcutta, to whose kindness I am indebted for many observations on earth-worms, informs me that he found, near Nancy in France, the bottom of the State forests covered over many acres with a spongy layer, composed of dead leaves and innumerable worm-castings. He there heard the Professor of "Amenagement des Forets" lecturing to his pupils, and pointing out this case as a "beautiful example of the natural cultivation of the soil; for year after year the thrown-up castings cover the dead leaves; the result being a rich humus of great thickness."

In the year 1869, Mr. Fish {5} rejected my conclusions with respect to the part which worms have played in the formation of vegetable mould, merely on account of their assumed incapacity to do so much work. He remarks that "considering their weakness and their size, the work they are represented to have accomplished is stupendous." Here we have an instance of that inability to sum up the effects of a continually recurrent cause, which has often retarded the progress of science, as formerly in the case of geology, and more recently in that of the principle of evolution.

Although these several objections seemed to me to have no weight, yet I resolved to make more observations of the same kind as those published, and to attack the problem on another side; namely, to weigh all the castings thrown up within a given time in a measured space, instead of ascertaining the rate at which objects left on the surface were buried by worms. But some of my observations have been rendered almost superfluous by an admirable paper by Hensen, already alluded to, which appeared in 1877. {6} Before entering on details with respect to the castings, it will be advisable to give some account of the habits of worms from my own observations and from those of other naturalists.

[First Edition, October 10th, 1881.]


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