Mysterious spectacular mounds found in the earth in tropical wetlands in South America are created by earthworms, researchers have found.
The densely packed, regularly spaced mounds cover large areas of the Orinoco Llanos in Columbia and Venezuela. Until now it was not known how they were formed.
A new study shows these mounds, called surales, are largely made up of earthworm casts, heaps of muddy soil ejected by their guts. This is the first research to describe their formation.