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Un-learning about Worms

Bill Meredith

"Education: that which discloses to the wise
and disguises from the foolish their lack of understanding."
-Ambrose Bierce, The Devil's Dictionary

It is a sad fact of life that many of the things we learn as children turn out not to be true. As a small child, I remember thinking I knew all about birds when I learned that robins migrate south for the winter, and that their return in March is one of the first signs of spring. By the time I got to college, I was a bit disillusioned to find that there are exceptions to all of the pretty rules I had learned earlier. I clearly remember our first field trip in ornithology class; it was January, and cold, and I heard a chirp that sounded like a robin. When I asked the professor, he remarked offhandedly that, yes, it was a robin, and that there are always a few of them that stay around all winter and don't migrate. It was one of those critical experiences we all have when we are forced to confront the realization that the world is more complicated than we thought.

Global warming is proceeding apace; this winter, the robins didn't even pretend to migrate. In previous winters I recorded them only occasionally when I went walking into the woods; this year, they were in the yard nearly every day, eating crab apples and Bradford pear fruits. In March, when they normally would have been returning from the south, I saw them hopping about in the brown-colored lawn with puzzled expressions on their faces because there were no earthworms. I had a similar expression on my face when I plowed the garden just before St. Patrick's Day and, for the first time in my memory, did not turn up a single earthworm. The worms, of course, were waiting for the spring rains; this was the driest March on record, and they had sense enough to be patient. Things seem to be getting back to normal in the past couple of weeks; rains have come, worms are up, and robins are happier.

Whenever I think of earthworms, my mind turns to Charles Darwin. Everyone knows he wrote the "Origin of Species," in which he presented the first defensible explanation of evolution; but most people are not aware that he wrote 17 other books. The last of these, "The Formation of Vegetable Mould by the Action of Worms," was his personal favorite; he worked on it, on and off, for over 40 years, and it was published the year before he died. "Vegetable mould" was the old British term for topsoil, and most of the "facts" we learned in school about how earthworms form topsoil came from that book. Darwin spent uncounted hours over those four decades counting earthworm burrows in his lawn and gardens, weighing the dirt castings the worms brought to the surface, and observing their habits; his gardener once remarked, "The poor Master must be losing his mind, for all he does is sit and stare at the ground." His estimates that between 6 and 12 tons of dirt were brought to the surface of an acre of ground each year were still quoted in biology books when I was in school.

In a lifetime of fishing, as well as teaching zoology for 41 years, I thought I had come to know a good deal about earthworms. Hence it came as a surprise recently to learn that they are not entirely beneficial; in fact, they have been found to be causing ecological problems in some forests. The parts of North America that were covered by glaciers in the Ice Age have no native species of earthworms; the ones now found 1 there, as well as many of the species in more southerly parts of the U. S., were brought from Europe, mostly by accident, in soil around potted plants. The 1 development of soils in forests is the result of the breakdown of leaves by fungi, which release nutrients into the soil. In the 12,000 years since the Ice Age ended, this breakdown went on slowly, and the native forest trees adapted to this slow rate of decomposition. The European earthworms, which include the common night-crawler, speed up the decomposition of leaf litter, releasing nitrogen and phosphate faster, and much of these nutrients wash away before the trees can absorb them. Ecologists in New England and Minnesota have recently found that alien earthworms have changed the soil enough that some rare plants are becoming extinct and the growth of several types of trees is slowing down because of stress on their root systems.

Thinking about this, it occurred to me that I had never read Darwin's book on worms, so I went to the Mount library to get it. The copy on the shelf was the 1896 edition, and it was a beautiful book ... red leather binding overlaid with marbled paper, and the upper edges of the pages gilded. An inscription on the flyleaf indicated that it had been donated to the college; it was probably one of a set of Darwin's books that the owner bought to display on his shelves. But it was a display of vanity, for it had never been read. The pages were still folded and uncut, as books were sold in those days. So I had the fascinating experience of being the first person to read a 110-year old book, carefully cutting the pages apart with a sharp knife as I went through it.

Much of Darwin's writing is dry and fact-laden, but he had a gift for eloquence; the last paragraph of the "Origin of Species" is famous for its near-poetic quality. The conclusion of the worm book is in a similar vein. He reminds us that the soil we see has passed countless times through the bodies of worms, and that their effect is immeasurable: "The plough is one of the most ancient and most valuable of man's inventions; but long before he existed, the land was in fact regularly ploughed by earth-worms."

As I grow older, I find it irksome to give up old knowledge. This is not unusual; old people are notorious for resisting new ideas. As David Brooks recently remarked, "Intellectual history moves forward in a hearse." So it is impossible not to wonder what Darwin would think of the new discoveries about the harmful effects of his beloved worms. He was a wise man, and my guess is that rather than clinging to old ideas, he would be intrigued. After all, progress in science has always involved the modification of previously held ideas, and it has always required the un-learning of what we thought were proven truths. Sic transitgloria mundi.

Read other articles by Bill Meredith