Earthworms and Wedgwood cousins
As with many of Darwin's research topics, his interest in worms spanned nearly his entire working life. Some of his earliest correspondence about earthworms was written and received in the 1830s, shortly after his return from his Beagle voyage, and his last letters about worms were written only months before he died in March 1882. In the same way that Darwin cast a wide net when seeking information on pigeon morphology, the action of climbing plants, and biogeography, Darwin wrote to friends and contacts near and far to collect information on worms. Some of his most faithful informants and observers of the actions of earthworms were members of his own family, in particular his nieces, Lucy and Sophy Wedgwood, the daughters of Emma Darwin's brother Josiah. Darwin relied on and valued the careful observations of these two young women, even going so far as to submit Lucy Wedgwood's observations for publication in the Gardeners' Chronicle.
Scientific evidence for the history of life
Darwin chose to study earthworms in order to fill out the details of his theory of evolution by natural selection. His book Fertilisation of Orchids (1862) was Darwin's "flank movement against the enemy"; it argued that the intricacies of adaptation could have arisen from natural selection working alone. Similarly, The Power of Movements in Plants (1880) was a study of incredible empirical detail that demonstrates Darwin's creative experimental methods. Darwin's study of earthworms was a treatise on the power of present day observations for making inferences about past events. The philosophy of a historical science (be it geology or evolutionary theory) was a subject that Darwin had contemplated from his earliest days as a naturalist. As his final published work, The Formation of Vegetable Mould through the Action of Worms was a fitting end to a lifetime of varied natural studies and theoretical work.
You can download the entire packet of reading materials here: Earthworms Source Pack
Darwin, C.R. 1840. On the formation of mould. Transactions of the Geological Society (Ser. 2) 5:505-509.
Darwin, C.R. 1881. The Formation of Vegetable Mould, Through the Action of Worms. London: John Murray. Chapters 1 and 3.
Letter 385- Sarah Elizabeth Wedgwood & Josiah Wedgwood to Darwin, 10 November 
Written by Emma’s sister at the behest of her father Josiah, this letter conveys the details of when and how parish fields around their home at Maer Hall in Staffordshire were fertilised.
Letter 8137- William Darwin to Charles Darwin, 1 January 1872
Darwin’s eldest son writes with detailed description of the effects of earthworm action on fallen slabs of stone at Stonehenge. In his reply of two days later, Darwin wrote, “Your letter & facts are quite splendid.—I cannot conceive how you could have observed so much without aid.” [Letter 8140, 3 January 1872]
This exchange of letters between Darwin and his niece Lucy, aged 26 at the time, demonstrates Darwin’s solicitation of information, his niece’s readiness to comply with his request, and his gratitude for her observations.
Letter 12745- Darwin to Sophy Wedgwood, 8 October 1880
Darwin writes to his niece Sophy, requesting her and her sister Lucy’s aid in observing earthworms on the heath near their home, and mentioning Lucy’s “well-known affection for worms". In her reply, Sophy drew on her own familiarity with worms, writing: “from my experience, I shd hardly have expected to meet with any worms in that stony sand, (or in peat either.) unless in such a case as grass roots, weeds, in a gravel path.” [Letter 12760, 15 October 1880]
Letter 13406- Mary Catherine Stanley (Lady Derby) to Darwin, 16 October 1881
Among pleasantries about the weather, Lady Derby remarks on her interest in earthworms and its significance.
Letter 13632- Darwin to John Murray, 21 January 1882
In his last letter touching on earthworms, written less than three months before his death, Darwin remarks on the degree to which evolutionary theory has penetrated young scientists working “in any branch of Biology.” Darwin likens the views of a disbeliever who reviewed Earthworms to those of the thinkers who stood against heliocentrism.
Gould, S.J. "A Worm for a Century and all Seasons" reprinted in Hen's Teeth and Horses Toes.
In an essay for Natural History magazine, Stephen Jay Gould argues for the importance of Darwin's last book and its centrality to Darwin's view of history.
1. What do you think of Darwin's letter to John Murray? What does Darwin make of the influence of his own theory on the discipline of biology?
2. How does Darwin request the help of his nieces? What does the tone of Darwin's correspondence with his nieces tell you about Darwin's domestic life and extended family?
3. How does Darwin praise the observational abilities of his son and nieces? What do you make of his relationship to them through the correspondence?
4. What do you think of Darwin's final book? Would you have expected this to be the final topic Darwin touched on in his scientific career? How does this topic relate to the rest of Darwin's scientific work?
To observe earthworms as Darwin did, you will need:
- several small plastic pots
- moist potting soil
- earthworms (which can be ordered)
- a string instrument (piano, upright base, violin etc.) and someone to play it
Put the earthworms into the clay pots, about 20-30 in each pot. Observe them first without playing any music. How are they moving? Do they react to movements of the pots? Do you have a baseline for their behavior to start the experiment?
Play music for the earthworms. Do they react? Why do you think Darwin wanted to carry out this experiment? Can you relate your own observations to the letter selections for this module?
Do the earthworms react to vibrations that touch the soil? What about vibrations in the air? What does this tell you about the way that earthworms 'hear'?
- make detailed observations of earthworms' movements and habits
- observe whether earthworms react to music
- discuss why Darwin did this experiment
- relate your experience to Darwin's discussion of earthworms in the correspondence
An example of this activity performed at Harvard University:
To learn about Darwin’s work on worms, the class collaborated with students at the New England Conservatory (NEC) to replicate some of Darwin’s experiments. The NEC students brought a bassoon, a piccolo, and a piano and our class brought two pots full of earthworms. Using these materials, we were able to imitate the experiments Darwin used to understand the hearing power of worms. In Chapter 1 of Vegetable Mould and Earth-worms, Darwin explained:
Worms do not possess any sense of hearing. They took not the least notice of the shrill notes from a metal whistle, which was repeatedly sounded near them; nor did they of the deepest and loudest tones of a bassoon. They were indifferent to shouts, if care was taken that the breath did not strike them. When placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly quiet.
In spite of the NEC student’s best efforts to incite movement in the worms by playing their instruments, the worms remained unaffected, just as Darwin had observed.
After satisfactorily illustrating that the worms did not notably react to any of the sounds Darwin mentioned, the students sought to observe the effect of vibrations upon worms. In Vegetable Mould and Earth-worms Darwin wrote:
Although they are indifferent to undulations in the air audible by us, they are extremely sensitive to vibrations in any solid object. When the pots containing two worms which had remained quite indifferent to the sound of the piano, were placed on this instrument, and the note C in the bass clef was struck, both instantly retreated into their burrows.
To replicate this portion of Darwin’s work, the students placed two thin plastic pots full of earthworms atop a piano. The NEC pianist then played all of the musical notes Darwin mentioned (along with a few pieces of music). A few of the worms in our experiment retreated slowly into the dirt, but our results were not quite as dramatic as those reported by Darwin. In spite of our lack of definitive results, this experiment provided a great opportunity to engage firsthand with Darwin’s work. Even better, this experiment can be easily recreated almost anywhere: all you need are some worms and some instruments. Try it now and see if your worms are reactive to sound and/or vibrations!
 Charles Darwin, Vegetable Mould and Earth-Worms (London: John Murray, 1881), 26.
 Ibid., 26-27.