MAY 11, 2016
by Brett Smith
Packed, evenly-distributed mounds can be found dotting large areas of Columbia and Venezuela, and a new study indicates these piles, known as surales, are mostly comprised of earthworm casts, or loads of muddy soil thrown out by their guts.
Published in the journal PLOS One, the new study made use of remote sensing means, satellite pictures and aerial photos captured by a drone to examine the landscape. The study team also compiled information on the physical and chemical makeup of soil to learn more around how surales form and develop. This data revealed earthworm casts make up as much as one-half of overall soil mass of surales, which vary in size from 2 to 16 feet across and from 1 foot to over 6 feet high.
Surales develop when large earthworms feed in mildly-flooded soils, putting casts down that grow into small 'towers' that reach above the water level. Each earthworm comes back over and over again to the same location to feed, place casts and to respire. As time passes, the small tower becomes a mound.
When piles already established are situated close together, the sink between them becomes packed and the mounds join together.
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