Earth(worms) First

Published March 1, 2000

Charles Darwin was one of the first scientists to show that earthworms have important effects on the chemistry and physical structure of soils. He and many scientists to follow noted that worms speed up the decomposition of plant litter and improve conditions for numerous microorganisms.

As many a backyard gardener knows, most plants benefit enormously from the presence of earthworms. Indeed, wherever plant life thrives, the ground is teeming with them. Did you realize that a grassland the area of a football field typically contains several tons of earthworms below the emerald surface?

Hundreds of experiments have shown that increased atmospheric carbon dioxide (CO2) promotes healthier and more productive grasslands. But what about its effect on other members of the ecological system?

Indeed, though CO2 in and of itself benefits the grasslands, it could become a net negative if CO2 is bad for worms. Many past studies have shown that increased atmospheric CO2 increases root growth, stimulates fungi activity, and increases soil moisture via an increase in water-use efficiency of plants. So perhaps the future looks “bright” for these below-ground members of the biosphere.

Several years ago, Zaller and Arnone elevated atmospheric CO2 from 350 parts per million (ppm) to 600 ppm in open-top chambers over a grassland near Basil, Switzerland. In the second year of the experiment, they collected and measured earthworm casts in an effort to assess worms’ overall activity.

The soil moisture had indeed increased with elevated CO2, and the lucky worms beneath increased their cast production by 35 percent.

Due to their extra activity, the carbon and nitrogen in the CO2-enriched soil was increased by 28 percent. The earthworms apparently found the world of elevated CO2 to their liking, and the plants above benefited further from their increased soil processing and turnover.

These same two scientists published another article recently with even more good news about CO2, earthworms, and the fate of future grasslands.

Using the same basic field design, Zaller and Arnone found that plants near the casts were much better off than those farther away, irrespective of CO2 enrichment. The best of all worlds was a location near an earthworm cast in the elevated CO2 environment!

An increased concentration of atmospheric CO2 is good for grasslands and great for worms, and both results produce positive feedbacks for the overall ecosystem.

The people and animals who depend on the world’s grasslands—and that means virtually all of us—should be thrilled with these results. And like the earthworms whose suffering it would no doubt cause, the Kyoto Protocol—which seeks to limit atmospheric CO2 concentration—should never see the light of day.

Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.


Zaller, J.G. and J.A. Arnone III, 1997. Activity of surface-casting earthworms in a calcareous grassland under elevated atmospheric CO2. Oecologia, 111, 249–254.

Ibid., 1999. Interactions between plant species and earthworm casts in a calcareous grassland under elevated CO2. Ecology, 80, 873–881.