How earthworms can digest plants that defeat other herbivores


Earthworms in rich organic soil. As they burrow, the worms consume soil in order to remove nutrients from decaying organic matter such as leaves and roots.
Dr. Manuel Liebeke, Imperial College London
Earthworms can digest plant material that most other herbivores cannot thanks to certain molecules in the earthworm gut that counteract toxins from the plant's natural defences.

The worms play and important role returning the carbon locked inside dead plant material back into the ground.

They drag fallen leaves and other plant material down from the surface and eat them, enriching the soil, and they do this in spite of toxic chemicals produced by plants to deter herbivores.

The scientists, led by Dr Jake Bundy and Dr Manuel Liebeke from Imperial College London, identified the proetctive molecules molecules, which have been named drilodefensins. They are essential for our own well-being as well as that of the worms, the scientists say.

"Without drilodefensins, fallen leaves would remain on the surface of the ground for a very long time, building up to a thick layer. Our countryside would be unrecognisable, and the whole system of carbon cycling would be disrupted," says Bundy.

Plants make polyphenols, which act as antioxidants and give the plants their colour; they also inhibit the digestion of many herbivores. Earthworms, however, are able to digest fallen leaves and other plant material, thanks to the ability of drilodefensins to counteract polyphenols. Dr Bundy and his team found that the more polyphenols present in the earthworm diet, the more drilodefensins they produce in their guts.

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