Earthworms Protect Gardens From Slugs, Research Finds

Earthworms, when present in healthy numbers in a garden’s soil, effectively protect the plants there from being consumed by slugs, according to new research from the University of Natural Resources and Life Sciences in Vienna.

Garden Swiss chard
Image Credit: Vegetable Garden via Flickr CC

An interesting finding, for those of us that like to garden. Slugs can be quite the pest from what I’ve heard, though I’ve only had issues with them once — with regards to cucumbers. And that was remedied pretty easily by raising the plants off the ground.

HealthHeathen has more:

Even though the earthworms don’t have direct contact with the slugs or the plant growth above, they seem to very effectively protect the plants via increased nitrogen content in the plants, as a result of the earthworms being present. The researchers also found that with increased plant diversity the amount of damage that the slugs did to individual plants was greatly lessened.

The research was done by using large incubators to simulate grassland environments where “the researchers could regulate the diversity of plant species and time the introduction of earthworms and slugs.” What was found was that the presence of the earthworms increased the nitrogen content of plants and reduced the number of leaves damaged due to slugs by 60%. And interestingly, even when the total leaf area damaged was compared, the slugs ate 40% less at high plant diversity than at low. That’s a significant improvement.

Lead researcher Dr Johann Zaller, elaborates: “Our results suggest that two processes might be going on. Firstly, earthworms improved the plant’s ability to protect itself against slugs perhaps through the build-up of nitrogen-containing toxic compounds. Secondly, even though these slugs are generalists they prefer widely available food and in high diverse ecosystems slugs eat less in total because they have to switch their diets more often since plants of the same species are less available. Therefore gardeners are to help protect earthworms by increasing plant diversity in the garden in order to keep slug damage low. In order to elucidate the mechanisms behind these complex interactions, all parts of an ecosystem need to be investigated.”

Certainly something to keep in mind. And of course, earthworms provide much more benefit to gardens than simply keeping slugs away. It’s well worth it, for a variety of reasons, to encourage their presence.

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