Nematodes? Four-fifths of all animals on Earth? Who's ever heard of nematodes.
Nematodes are threadlike worms that range in length from a millimeter to a meter. A handful of loam might contain a thousand. They live virtually everywhere -- soil, water, desert sand, arctic ice, hot springs, and as parasites of plants and animals. Pinworms and hookworms, familiar parasites of humans, are nematodes. C. elegans, that favorite research animal of biologists, is a nematode.
In the 1914 edition of the Yearbook of the United States Department of Agriculture, the American parasitologist N. A. Cobb wrote:
If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes and oceans represented by a thin film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.I've always loved this thought experiment, that ghostly nematodean world. Bingo! Everything that isn't part of a nematode vanishes. And there, at least for an instant until it disperses, is the shadow world. The giant hollow sphere. The mountains, valleys, oceans, rivers. The plants. The animals. Spookily represented by worms.
Four-fifths of all animals on Earth! E. O. Wilson adds: "Can anyone believe that these little creatures are just there to fill space?" He means, of course, that we are all of a piece. All necessary. All part of a balance that has been billions of years in the making.