The Lowly, but Ubiquitous, Worm

April 18, 2016

One advantage of raising children is that you get to relive some of the fun of your own childhood. I've always enjoyed reading children's picture books, my favorites being the books by Richard Scarry. One memorable character from his many books is Lowly Worm, an anthropomorphic earthworm wearing a Tyrolean hat and a single shoe. You can see him in action in various YouTube animations.[1]

Worms are a part of popular culture in such phrases as "book worm," another name for a bibliophile. Not surprisingly, I was a book worm in my youth, although now I do nearly all my reading from a computer screen. I can't be called a computer worm, since that term is already used to describe a form of malware. The first, and most famous, computer worm, is the Morris worm that infected the early Internet in 1988.

There's a joke that a collection of aphorisms spoken by Ludwig Wittgenstein as he paused to tie his shoes would be a best selling book. Wittgenstein had something to say about worms, "May God enlighten me. I am a worm, but through God I become a man."[2] US President, Franklin Delano Roosevelt, also has a memorable worm quotation, " I sometimes think we consider too much the good luck of the early bird and not enough the bad luck of the early worm."

A circa 1919 portrait of US President, Franklin Delano Roosevelt (FDR), when he served as Secretary of the Navy. FDR was the only American president to serve more than two terms. He died shortly into his fourth term. The Twenty-Second Amendment, ratified in 1951, limited the presidency to two terms (Photograph from the United States Library of Congress Prints and Photographs Division, via Wikimedia Commons.)

As we've learned in elementary school science, the lowly earthworm (an Annelid of the class oligochaeta) is of great benefit to mankind. It's even been suggested that earthworms would make a good protein supplement for humans. Fortunately, the Wikipedia page about the Diet of Worms is on a different topic altogether.

Earthworms play a major role in soil improvement by conversion of organic matter, such as leaves, into humus. Earthworm excrement contains a rich mixture of nitrates, phosphates, and potassium that fertilize plant growth. Earthworm burrows aid in the aeration and drainage of soil.

The earthworm was the topic of Charles Darwin's last book, "The formation of vegetable mould through the action of worms with observations on their habits," which was published in 1881, just six months before he died. This book addressed not only the ecology of worms, but the question of how intelligent they might be. Darwin performed some simple experiments to elucidate worm intelligence.

This book contained, also, an estimate of the areal density of worms in soil. Darwin's number, 53,000 worms per acre (13/square meter), is somewhat lower than current estimates that range from 250,000-1.7 million depending on soil quality.

Evolution of man from the worm, with a caricature of Charles Darwin. (A Wellcome Trust image, photo number, L0003921, via Wikimedia Commons.)

Earthworms are everywhere, but data on their precise geographical distribution have been lacking. To remedy this uncertainty, researchers from eight European countries collected information on earthworm communities, and they mapped their biodiversity.[3-4] The members of the research team were from the National Institute for Public Health and the Environment (Bilthoven, The Netherlands), the Joint Research Centre (Ispra, Italy), the University of Parma (Parma,Italy), ECT Oekotoxikologie GmbH (Flörsheim am Main, Germany), the Centre for Ecology and Hydrology (Lancaster, UK), the James Hutton Institute (Dundee, UK), University College Dublin (Belfield, Ireland), the Agri-Food and Biosciences Institute (Belfast, UK), Blackshaw Research & Consultancy (Devon, UK), Agrocampus Ouest-INRA SAS (Rennes, France), the University of Rennes, (Rennes, France), the University of Vigo (Vigo, Spain), the Universidad Complutense de Madrid (Madrid, Spain), the University of Coimbra (Coimbra, Portugal), the University of Ljubljana (Ljubljana, Slovenia), Aarhus University (Silkeborg, Denmark), and Alterra, Wageningen UR (The Netherlands).[3]

The early bird and his worm. In this case, the bird is a European robin (Erithacus rubecula), and the worm is the common earthworm (Lumbricus terrestris). (Photo by Rasbak, via Wikimedia Commons.)

Although few likely noticed, 2015 was the "International Year of Soils."[4] It's amazing how much biodiversity exists in the topmost layer of Earth's surface. Every gram of soil contains millions of organisms, and soils contain more than a quarter of Earth's species, but there have been few published studies on soil ecosystems.[4] Says María Jesús Iglesias Briones, a co-author of the study at the University of Vigo,

"The classification of edaphic invertebrates and their distribution patterns have not received priority for funding, meaning that a lot of information from unpublished studies has not been digitised."[4]

In their studies, the research team assembled existing earthworm data from 3838 sites in eight European countries.[3] Of these locations, 1,423 were from France alone, a consequence of substantial French funding in this area.[4] Using the computer technique of multiple regression, they were able to relate earthworm density to such factors as soil characteristics, land use, vegetation and climate.[3] In the end, they were able to produce some impressive graphics, two examples of which are shown below.[3]

Earthworm abundance. (From Rutgers, et al.[3]) (Click for larger image)

Earthworm diversity. (From Rutgers, et al.[3]) (Click for larger image)

The analysis determined that climate is more important than geography to earthworm distribution, while land use was an important factor in determining their demography and diversity.[3] Says Briones, "We hope that studies such as this one put a greater weight on the need to understand the diversity of these invertebrates that are so important to the proper functioning of soils."[4]

References:

1. The Busy World of Richard Scarry - Lowly Breaks His Leg, YouTube Video, Uploaded February 25, 2010.
2. Kai-man Kwan, "Rainbow of Experiences, Critical Trust, and God: A Defense of Holistic Empiricism," Continuum International Publishing Group (New York, August, 2011), p. 29 (via Google Books).
3. Michiel Rutgers, Alberto Orgiazzi, Ciro Gardi, Jörg Römbke, Stephan Jänsch, Aidan M. Keith, Roy Neilson, Brian Boag, Olaf Schmidt, Archie K. Murchie, Rod P. Blackshaw, Guénola Pérès, Daniel Cluzeau, Muriel Guernion, Maria J.I. Briones, Javier Rodeiro, Raúl Piñeiro, Darío J.Díaz Cosín, J.Paulo Sousa, Marjetka Suhadolc, Ivan Kos, Paul-Henning Krogh, Jack H. Faber, Christian Mulder, Jaap J. Bogte, Harm J.van Wijnen, Anton J. Schouten, and Dick de Zwart, "Mapping earthworm communities in Europe," Applied Soil Ecology, vol. 97 (January 2016), pp. 98-111.
4. The first European earthworm map is drawn, Spanish Foundation for Science and Technology Press Release, February 24, 2016. Press release in Spanish.