HAS THE WORM TURNED?

It may surprise some people to know that earthworms are not native to the North American continent. They were introduced here by early colonists when they brought earthworm cocoons embedded in potted plants they brought with them. Through agriculture, fishing and on their own earthworms have been disseminated across the continent. In some forested area they are spreading at the rate of about seven meters a year.

The glaciated forests of North America existed for millions of years without earthworms as part of their soil makeup. These forests depend on a rich top soil layer of slowly composting leaf litter and a unique microbial population to supply nutrients to the thin mineral soils. As the worms invade an area, they hasten the breakdown of the leaf litter. The trees of the northern forests of the US depend on the leaf litter to help tree seedlings to survive. The thick leaf litter provides protection against temperature extremes, moisture loss and protection from browsing animals. The leaf litter is essential to seedling survival. So as the leaf litter layer is destroyed by earthworms, the reproductive success of the forest is compromised.

Normally, this earthworm activity has been seen as a good thing because it hastens nutrient liberation and spreads nutrients deep into the soil. However, this conclusion was reached based upon the studies of Charles Darwin from the limited sample of the English countryside. There is no indication that he knew earthworms were not universally distributed. What may be good for a damp cold climate may be less beneficial to a different environment. The reported thick top soil of the American mid-west may have existed because there were no earthworms to hasten decomposition. We'll never know since they are now ubiquitous.

There is also evidence that the microbial makeup of the northern soils is changed with invasions of the earthworm. Some of this is undoubtedly due to the changes in leaf litter and soil nutrition. But there is growing suspicion that the collection of earthworm mucus within the soil structure may also account for some of the changes in microbial balance.

Researchers at the Hebei Agricultural University in China examined earthworm mucus for antibacterial activity and found a short peptide (small protein like chemical) that possessed antibacterial properties against several common bacterial strains. What role this chemical plays in the actual protection of the earthworm, the amount produced and how broadly this peptide protects against bacteria is yet to be determined.

Once again we see that "Man doesn't know what he doesn't know."