Large Mystery Mounds in South America are Created by Earthworms

Posted on May 16, 2016

Surale in wetlands in South America

Earthworms have been linked to mysterious mounds found in tropical wetlands in South America. These mounds, known as surales, cover large areas of the Orinoco Llanos in Columbia and Venezuela. The scientists say the mounds are created from earthworm castings - muddy soil ejected from the guts of earthworms.

Researchers used remote sensing techniques, satellite images and aerial photographs taken by a drone to study the landscape. They also collected data on the physical and chemical makeup of soil. The data indicates that earthworm casts account for up to one-half of total soil mass of surales, which vary in size from 0.5 to 5m in diameter and from 0.3 to more than 2m.

The Surales are formed when large earthworms feed in shallowly flooded soils. As they feed they deposit casts that form 'towers' above water level. Each earthworm returns repeatedly to the same spot to deposit casts and over time the tower becomes a mound.

Professor José Iriarte, an author of the study from the University of Exeter, who worked on the study, says in a statement, "This exciting discovery allows us to map and understand how these massive landscapes were formed. The fact we know they were created by earthworms across the seasonally flooded savannahs of South America will certainly change how we think about human verses naturally-built landscapes in the region."

A research paper on the surales was published here in the journal, PLOS One. The paper has more images of the surales in its figures section.

Photo: Professor José Iriarte