Are earthworms, long held to be the (invertebrate) backbone of healthy soil structure, in fact responsible for emitting polluting greenhouse gasses? An international team of researchers believe so, after having studied whether the creatures are "a net source or sink of greenhouse gasses."

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According to the results of a study published in this month's Nature Climate Change journal, humble earthworms which help sequester carbon in soils through consuming decaying organic matter and storing its carbon in their 'cast', are also responsible for releasing major greenhouse gasses, including carbon dioxide and nitrous oxide. Researchers from the United States, Colombia and the Netherlands said that worms' influence is expected to increase over coming decades as their numbers increase.

Worms are ranging into new areas of North America, though soil degradation elsewhere may limit their activity. Through their burrowing, worms affect the amount of carbon stored in soil, altering its structure and improving drainage, but the worms themselves produce gasses their activity affects soil microbes, which also releases greenhouse gasses.  

However, although researchers found that increasing number of worms in soil increased emissions of both carbon dioxide and nitrous oxide, and stated "Our results suggest that although earthworms are largely beneficial to soil fertility, they increase net soil greenhouse-gas emissions," they added that, overall, the picture is not so clear. In fact, earthworms in soil can produce extra emissions of one type of greenhouse gas, while reducing another.

Worms were shown to increase the emissions potential of soil by 16 percent. Even so, though they may be net producers of greenhouse gasses, in the global scheme of emissions, earthworms' effect is comparatively small.