Earthworms eat seeds and seedlings, scientists have found.
The discovery they eat live rather than just dead plants will change the way we think about earthworms, which had been thought to benefit plants by recycling soil nutrients.
It may offer a way for gardeners and farmers to encourage more earthworms into their soil, for example.
But it also means invasive earthworms could be reducing populations of plants in once pristine soils.
Confirmation that earthworms feed on living plants is published in the journal Soil Biology and Biochemistry by Dr Nico Eisenhauer of the Georg-August-University Göttingen in Germany.
With colleagues, Dr Eisenhauer made the discovery studying the behaviour of Lumbricus terrestris, an anecic earthworm that inhabits soils around the world.
Originating in Europe, the worm occurs in grasslands, agricultural fields and forests and is invading soils across the US, Canada, Australia and New Zealand.
Previous studies have shown that some earthworms will swallow plant seeds, while others appear to collect seeds, burying them in their burrows.
But it was not clear why, whether the earthworms were actually seeking rotting seeds, or whether they derived any nutritional benefit from the habit.
So Dr Eisenhauer set up a series of experiments to find out, offering earthworms housed in the lab a selection of food, including seeds and seedlings from different plant species.
The results were startling.
The earthworms selectively fed on slow-germinating, nitrogen-rich seeds and seedlings, actively ingesting the plant material, killing the young plant.
Earthworms allowed to feed on live plants gained weight, and their performance would vary depending on what plants they were offered, such as legumes or grasses, suggesting they do derive nutritional benefits from such a diet.