3D scanning reveals the burrowing of earthworms

Earthworms play an important role in healthy soils. As earthworms move through the soil, they create burrows that act as channels for water, air and plant roots. Earthworms also mix soil and help make nutrients more available to plants and microbes.

X-ray scanning the earthworm burrows

Despite their importance, it has been difficult to measure how much earthworms actually burrow under field conditions, since their activity takes place hidden below ground. But now, researchers at the Department of Soil and Environment have tested a method that allows them to monitor the worms' burrowing directly in the field.

The method uses specially designed cylinders with openings on the top, bottom and sides, allowing earthworms to move freely in and out. The cylinders are installed in the soil, removed periodically for X-ray scanning, and then immediately returned to the field. The scans produce detailed 3D images that make it possible to identify and analyse earthworm burrows, including their volume, branching patterns and shape.

− By comparing scans from different time points, we could determine when new burrows were created, whether existing burrows remained open, and when burrows disappeared. This also made it possible to calculate burrowing rates. Based on burrow diameter, we could further distinguish between burrows likely created by different types of earthworms, says PhD student Rebecca ter Borg, who led the study.

Earthworms at different depths

Some species of earthworms live mainly in the upper 30 cm of soil and feed on organic matter in the soil, while others create much deeper burrows. The shallow-dwelling species are called “endogeic” earthworms, while the deep-burrowing species are known as “anecic” earthworms. 

− The study also revealed clear differences between earthworm groups. Anecic earthworms typically created few large, vertical and long-lasting burrows, accounting for around 40% of the total burrow volume. Endogeic earthworms, in contrast, produced many smaller and more temporary burrows. says Rebecca ter Borg.

A method opening up new possibilities

The cylinders were tested in a grassland field in Uppsala and scanned three times between spring and autumn. The results showed that burrowing rates varied during the season and were highest when soils were moist. Using these measurements, the researchers estimated that earthworms would need roughly 20–40 years to burrow through every cubic centimetre of topsoil in the field.

According to the researchers, the method provides new opportunities to study how earthworm activity changes over time and under different environmental conditions. Future studies could investigate how burrowing responds to soil moisture and temperature, how earthworm activity recovers after tillage, and how earthworms are affected by climate extremes.

− Through this method, we can increase our understanding of how earthworms react to, for instance, soil moisture, temperature, and disturbances such as tillage. This allows us to better understand how future climate, land use, and farming practices will affect the worms and the soil functions they support. This knowledge could help farmers choose management practices that promote earthworms as 'free laborers' in the soil, says Rebecca ter Borg.

More reading

Scientific article: Quantification of field earthworm burrowing rates using repeated X-ray scanning of open soil cores