Earthworms happily munch through leaves that are toxic to other plant-eaters -- and how they do it has always been a mystery.

But researchers said Tuesday that the worms produce special compounds in their gut to counteract plant toxins created precisely to repel hungry herbivores.

"Earthworms possess a class of unique surface-active metabolites in their gut, which we term 'drilodefensins'," a team reported in the journal Nature Communications.

The slimy creatures' long-kept secret has been uncovered through molecular microscopic analysis of their gut fluid.

Plants produce chemicals known as polyphenols, which act as antioxidants and give plants their colour, but also act as a shield by inhibiting digestion in many herbivores.

Earthworms are recycling specialists, eating fallen leaves and other plant material and returning the life-giving carbon locked up in the waste back to the soil.

But how they tolerate polyphenols has long left specialists scratching their heads.

A team led by Jake Bundy and Manuel Liebeke from Imperial College London found drilodefensins in the guts of 14 earthworm species, but not in other closely-related groups like leeches and sewage worms.

"For every person on Earth there is at least one kilogramme (2.2 pounds) of drilodefensins present within the earthworms that populate the world's soils," Imperial said in a statement.

"Without drilodefensins, fallen leaves would remain on the surface of the ground for a very long time, building up to a thick layer," it quoted Bundy as saying.

"Our countryside would be unrecognisable, and the whole system of carbon cycling would be disrupted."

The compound's name was derived from the Latin name for the order of invertebrates containing earthworms: Megadrile.
Source: AFP