How do worms move in the dirt?
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Earthworm Locomotion in Soil: Mechanisms and Dynamics
Peristaltic Crawling: The Primary Mode of Earthworm Movement
Earthworms primarily move through soil using a method known as peristaltic crawling. This involves the sequential contraction and relaxation of their longitudinal and circular muscles, creating waves of shortening and thickening followed by thinning and lengthening along their hydrostatic skeleton. These peristaltic waves propel the earthworm forward and allow it to navigate through soil efficiently3 6 8.
Soil Displacement and Burrow Formation
As earthworms move, they displace soil particles around them. Studies using particle image velocimetry (PIV) have shown that soil displacement is more significant radially (to the sides) than axially (in front of the worm's head). This radial displacement helps in forming and expanding burrows. Notably, Lumbricus terrestris displaces more soil compared to Aporrectodea longa, both axially and radially1. Earthworms ingest small cores of soil and then flex their muscles to expand these holes, creating burrows with compacted zones around them5.
Environmental Responses: Humidity and Soil Compaction
Earthworms' movement is influenced by environmental factors such as soil moisture and compaction. For instance, enchytraeid worms move downward in response to drying soil surfaces, seeking moister layers below. This behavior is particularly evident in peat soils but less so in mineral soils2. Additionally, soil compaction significantly affects earthworm burrowing. Higher soil compaction levels (up to 600 kPa) reduce their ability to burrow, as observed in controlled experiments5.
Lateral Bending and Buckling for Enhanced Locomotion
Beyond peristaltic crawling, earthworms also utilize lateral bending and buckling to aid their movement. These dynamics help them anchor their bodies to the walls of their burrows, providing additional propulsion and allowing them to navigate around obstacles. This strategy is particularly useful in confined environments and enhances their ability to move through diverse terrains8.
Robotic Applications Inspired by Earthworm Locomotion
The principles of earthworm locomotion have inspired the development of robotic systems designed for underground exploration. Robots mimicking peristaltic crawling can navigate through soil and confined spaces effectively. These robots use expandable units to increase friction with their surroundings, similar to how earthworms move3 6. Additionally, incorporating lateral bending and buckling mechanisms into these robots can further improve their mobility and adaptability in various environments8.
Conclusion
Earthworms exhibit a complex and efficient mode of locomotion through soil, primarily using peristaltic crawling complemented by lateral bending and buckling. Their movement is influenced by environmental factors such as soil moisture and compaction. Understanding these mechanisms not only provides insights into soil ecology but also inspires the design of advanced robotic systems capable of navigating challenging underground environments.
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Most relevant research papers on this topic
Quantitative image analysis of earthworm-mediated soil displacement
Particle image velocimetry (PIV) effectively quantifies soil displacement by earthworms, with Lumbricus terrestris displacing more soil than Aporrectodea longa.
An underground explorer robot based on peristaltic crawling of earthworms
The peristaltic crawling robot, with its parallel links and dustproof covering, is suitable for underground exploration and can be controlled in 3D.
On the Movement of Wireworms of the Genus Agriotes Esch. (Coleoptera, Elateridae) on the Surface of the Soil and Their Sensitivity to light
Wireworms can move on the surface of soil without food, but their sensitivity to light and humidity prevents their emergence into high humidity air.
Soil management to prevent earthworms from riddling irrigation ditch banks
Compaction and using subsoil for irrigation ditch banks can reduce earthworm burrowing and water loss in ditches.
A 3D printed hydrostatic skeleton for an earthworm-inspired soft burrowing robot.
This 3D printed hydrostatic skeleton, based on the earthworm's hydrostatic skeleton, allows a small diameter, peristaltic-moving robot to move through soil.
Movement of First-instar Western Corn Rootworms (Coleoptera: Chrysomelidae) in Soil
First-instar western corn rootworms exhibit more vertical movement than horizontal movement in uncompacted soils, with more movement towards the CO2 source in the presence of CO2.
Highly CitedLateral bending and buckling aids biological and robotic earthworm anchoring and locomotion
Lateral bending and buckling in earthworms aids in anchoring and locomotion in diverse terrain, improving the performance of low-cost soft robotic devices in diverse environments.
Crawling of worms
The modified theory of worm crawling better aligns with experimental observations, reducing the maximum crawling velocity by requiring a time rate of change of tension less than a prescribed bound.
Burrowing dynamics of aquatic worms in soft sediments
Aquatic worms use elongation-contraction and undulatory strokes to move faster in sediments, utilizing higher drag anisotropy to navigate heterogeneous sediment beds.
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