Using soil hydromechanics to predict global earthworm distribution

Researchers develop a mechanistic biomechanical model that highlights strong correlation between habitat suitability and observed distributions for key subterranean "ecological engineers"

GBIF-mediated data resources used : 72,013 species occurrences
Lumbricus terrestris
Lumbricus terrestris Linnaeus, 1758 observed in Baltimore, MD, USA by akamediancat (CC BY-NC 4.0)

Earthworms are considered important "ecosystem engineers" as the soil biopores they form by burrowing can serve as pathways for water flow, aeration and reuse by growing roots. Previous research has suggested, for example, that earthworm activity may enhance certain crop yields by up to 25 per cent.

To study how earthworms disturb soils, a Swiss team of researchers started by calculating that the maximum pressure sustained by a worm hydroskeleton was 200 kilopascals (kPa). Applying this measure to global data on soil moisture and texture, they then modeled 0.1 degree grids around the world to identify where earthworms could burrow based on mean expansion limit pressures. After removing regions with permafrost, acidic pH, sand content and other limiting factors, they fine-tuned their mechanistic biophysical model to predict hospitable soil zones delineating the potential for earthworm migration in changing climates.

Using GBIF-mediated earthworm data they tested the predicted distributions against observed occurrences, finding that 86 per cent of reported earthworm presences agreed with the model classification. Upon examining the remaining false negatives, however, the authors found that these records often corresponded to local geographical features, such as river banks and anomalous precipitation zones.

Ruiz SA, Bickel S and Or D (2021) Global earthworm distribution and activity windows based on soil hydromechanical constraints. Communications Biology. Springer Science and Business Media LLC 4(1). Available at: