Earthworms Protect Plants
Its strange but True, earthworms have become the new secret weapon in protecting plants against slugs.
Having earthworms present in the soil is believed to help reduce the slugs eating plant leaves, as it increases the plants ability to take in nitrogen thus keeping the slugs at bay.
Tests have shown that the presence of earthworms in the soil have significantly reduced the number of leaves damaged by as much as 60 per cent. Scientists have also recorded a decrease in slug activity be increasing plant diversity but to a much lesser extent.
Dr John Zaller, an Austrian expert, from the University of Natural Resources and Life Sciences in Vienna, said:
“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.”
The research is reported in the online journal BMC Ecology. The scientists carried out the study in large incubators designed to simulate grassland environments. A range of grasses, herbaceous flowering plants and legumes (beans) were planted.
Spanish slugs, Arion vulgaris, were then introduced and allowed to roam freely. The slug, which grows to a length of 15cm, is one of the 100 most destructive invasive species in Europe and considered a major pest.
“Slug herbivory was significantly affected by both earthworms and plant species composition,” the researchers concluded in their paper.
“Slugs damaged 60% less leaves when earthworms were present, regardless of the species composition of the plant communities. Per cent leaf area consumed by slugs was 40% lower in communities containing 12 plant species.”
Grasses were generally avoided by the slugs, said the scientists.
A major upside to this story is the decrease in slug poisons that will be required to keep these pests under control. In my opinion any decrease in harmful poisons in the environment should be promoted.