The Formation of Vegetable Mould Through the Action of Worms, with Observations on Their Habits
, by Charles Darwin. (Free: available on iBooks and Kindle)

Reviewed by Virginia Hughes (guest reviewer)

Charles Darwin wrote many books and many types of books, the most famous of which you can download for free on iBooks or

Kindle
. How to choose?

If you want a really good story, go with Voyage of the Beagle, the charming journal Darwin kept while working as a naturalist on a ship that went
from England to South America, Tahiti, Australia, the tip of Africa and back. The first sentence is enough to pull you in:

The neighbourhood of Porto Praya, viewed from the sea, wears a desolate aspect.

If you’re looking for scientific import, nothing beats Darwin’s On the Origin of Species, the book that outlined his theory of natural selection
and would forever change biology. You might also try The Descent of Man for provocative ideas about race, gender, and sex, or
The Expression of the Emotions in Man and Animals for its lively photographs of faces that would inspire a future science of lie-detection.

It’s hard to think of a reason to read Darwin’s last book, The Formation of Vegetable Mould Through the Action of Worms, with Observations on Their Habits, unless you’re curious about exactly those things.
But for all you vermiphiles, there’s probably no better format for this volume than an e-book.

Darwin began

thinking about worms

in October of 1837, a year after disembarking the Beagle, when his uncle Josiah told him a curious story. Three years before, Jos had spread a
layer of cinders on a field near his home in the English countryside. Since then the cinders had sunk several inches and been replaced with a layer of fine
and uniform particles of soil known as vegetable mould. Could it be the work of the worms?

Intrigued, Darwin spent a few weeks closely observing his uncle’s fields. Sure enough, he discovered that the grass was littered with tiny cylindrical castings of worms. The next month, he formally presented his uncle’s idea to the Proceedings of the Geological Society of London: The digestive process of earthworms, en masse, is responsible for creating the vegetable
mould that helps crops grow. In this way, Darwin said, the lowly worm is a “geological power.”

That short paper planted a seed for a more substantial book about worms but, because of his many other writing projects, Darwin didn’t get around to
finishing it for 44 years. The book isn’t terribly long—some 222 pages on my iPad—but after reading a few pages I thought it might take 44 years to finish.

For better or for worse, the first two chapters—Habits of Worms and Habits of Worms Continued—feel like a transcription of Darwin’s
laboratory notebook. Some of his experiments are fun to read about, like when he exposed his potted household worms to the noise of a metal whistle, a
bassoon, piano banging, and shouting, all to prove that the critters were deaf. Other observations are not so fun, like the 23 pages describing which end
of a leaf a worm pulls into its burrow (for English plants: 80 percent were tugged from the tip, 9 percent from the base, and 11 percent from the middle).
Even in the tedious sections, though, the narration has a satisfying intellectual payoff. For example, Darwin uses the worm’s leaf-pulling methods—which
are neither random nor instinctual—to argue that the animals have some level of intelligence.

After 86 pages of worm habits, Darwin finally gets into the meat of the theory, describing in detail the soil observations that he made at his uncle’s
house and in the decades since. The next chapters are more historical and thoughtful, asking how worms may have played a part in the “burial of ancient
buildings” and the “denudation of the land.” It may have been no coincidence that Darwin chose decomposition as his final scholarly subject. By that time
he was old, sick and beginning to talk a lot about his own death. He died in April 1882, six months after Worms was published.

While slogging through the book, I kept wondering how it could have been so popular, selling

thousands of copies within weeks. Not only that, but Darwin apparently received a lot of fan mail. Readers sent him all sorts of their own stories and questions about earthworms.

Perhaps, rather than a well-paced narrative meant to be read cover to cover, Worms was bought as a handy reference book. Back then, after all, if
you saw a strangely shaped worm mound in your backyard garden, you couldn’t do a Google image search to diagnose it.

Thinking of it that way, maybe Worms was a proto-Wikipedia. Darwin constantly references the worm writings of other naturalists, just like
Wikipedia’s numerous footnoted citations. Each chapter begins with a paragraph of disjointed clauses that outlines the ideas within, just like the
hyperlinked contents box at the top of every Wikipedia page. And you can read the book’s chapters in practically any order—easy as scrolling down a browser
window.

Actually, reading Worms the e-book is arguably better than reading about worms on Wikipedia. Unlike Wikipedia, I could bookmark multiple pages,
highlight passages and write notes in the margins. Best of all, I was never left wondering about the validity of the source material: This is the
authoritative voice of one of the greatest biologists of all time.

So if you’re into worms, by all means download Worms and crawl into its deep, sleepy passages. If you’re not into worms, just read the Wikipedia summary.

Virginia Hughes
is a science writer based in Brooklyn. Her work has appeared in Nature, New Scientist and Popular Science, and her blog Only Human is part of National Geographic magazine’s Phenomena. Follow her
on Twitter.