To uncover how they play this role Darwin threw himself at his worm studies with as much childlike enthusiasm as he could muster; he was, until the day he died, eager to learn and full of ideas to help him do so. He set about a series of experiments to test the senses of worms; he had his children play instruments to them, his wife (who was trained by Chopin) played the piano to an audience of worms, light was shone on them, and they were vibrated, blown on and tickled. His conclusions:
‘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 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’
Darwin measured how much material they would ingest (eat), and how much they egested (pooped). He estimated how many worms there were on average in a given amount of soil, showing that all the soil in Britain ‘has passed many times through and will again pass many times through, the intestinal canals of worms’.
The rate at which worms process the soil can explain how ancient ruins are buried: Darwin calculated that worms push up eight tonnes of earth through the casts at the entrances of their burrows. He even carried out experiments to show this could happen within a human lifetime, he laid a stone in his garden, which was not to be disturbed, and measured the rate at which the earth was raised around it.
Darwin showed for the first time that worms increase the fertility of soils by aerating and mixing rotting material, this allows better root growth and water retention. By doing so he revolutionised compost heaps everywhere!