Ask most organic gardeners to list the indicators of a healthy soil and most will mention the presence of earthworms somewhere in their answer. We all know that worms are found where the soil is good, but few really know why.

Amy Stewart seeks to enlighten us in her wonderfully readable book The Earth Moved. Okay, so worms might not be the most appealing subject-matter for many readers, but this is a must-read if you've got a garden and care about what happens in it, or are intrigued by the idea of vermicomposting, or like me have just acquired your first wormery. In fact even those who have a problem with the idea of a book about our wriggly friends should get over it - the role of the apparently humble earthworm in our lives is much more significant than may be apparent at first glance.

Stewart uses the work and writing of Charles Darwin as a constant touchstone, and little wonder. In 1881 Darwin published 'The Formation of Vegetable Mould', the result of extensive and painstaking scientific research into earthworms. His passion and knowledge is recounted with evident enthusiasm here, and put into the context of present-day science and thinking, which shows Darwin's own science to have been remarkably robust. This is not to say that The Earth Moved is merely a rehash of Darwin's work - far from it. There is much to learn, from physiological secrets to potential uses for such noble tasks as cleaning up sewage and other pollution, with some cautionary tales in between - as with most of nature man's intervention can often have unforeseen and disasterous results, and even something as small as a worm can bring the biggest forests to their knees.

It's no exaggeration to say that earthworms play a critical role in our lives, and Amy Stewart does a first rate job of restoring them to their rightful place in the affections of the reader. Highly recommended.