Bristles Facilitate Movement

a brown and purple earthworm slides around a light brown log

Biological Strategy

Segmented worms

AskNature Team

Image: Katja Schulz / Flickr / CC BY - Creative Commons Attribution alone

Move in/on Solids

To obtain needed resources or escape predators, some living systems must move on solid substances, some must move within them, and others must do both. Solids vary in their form; they can be soft or porous like leaves, sand, skin, and snow, or hard like rock, ice, or tree bark. Movement can involve a whole living system, such as an ostrich running across the ground or an earthworm burrowing through the soil. It can also involve just part of a living system, such as a mosquito poking its mouthparts into skin. Solids vary in smoothness, stickiness, moisture content, density, etc, each of which presents different challenges. As a result, living systems have adaptations to meet one, and sometimes multiple, challenges. For example, some insects must be able to hold onto both rough and slippery leaf surfaces due to the diversity in their environment.

Search this Function

Animals

Kingdom Animalia (“having breath or soul”): Mammals, reptiles, sponges, corals, insects, birds

This kingdom captures a staggering variety of life—from the smallest coral polyp to the largest elephant. Although animal body shapes and life histories vary, there are a few defining characteristics. Animals are heterotrophs, meaning they gain energy from eating other organisms, and have developed from single-celled ancestors to highly diversified and coordinated multicellular forms. Unlike plant and fungi cells that have rigid cell walls, animal cells are bound by more flexible combinations of proteins. Most animals have cells organized into tissues and are able to move within their environment.

Search this Living System

Short rearward-pointing bristles on the body of an earthworm make rectilinear motion possible by grabbing the ground as the worm slides.

Introduction

In the soil beneath our feet, an unlikely champion is busy at work, churning through the earth and aerating the soil as it goes. The earthworm is a humble creature, but its contributions to the health of the planet are many.

This humble hero is able to move through the soil thanks to a clever system of short, rearward-pointing bristles. By grabbing the ground as it slides, the earthworm is able to inch its way forward, aerating the soil as it goes.

The Strategy

Earthworms move by stretching and squeezing alternate parts of their long, cylindrical trunk. Each region of stretch or squeeze is then moved rearward. This system of movement is called peristalsis.

In order for peristalsis to be effective, the trunk needs some device so it slides more easily forward than rearward.

For earthworms, setae, short rearward-pointing bristles, provide that crucial asymmetry. The setae are located in rows along the length of the earthworm’s body. As the earthworm moves, the setae grab the ground and help the worm to inch forward. At the same time, the setae brush backwards against the soil, helping to loosen it and aerate the earth.

The Potential

The setae of the earthworm could be emulated for use in a variety of applications. They could be adapted for use to help loosen compacted soil, making it easier to till or excavate. Setae-inspired structures could also be used to help aerate soil.

In addition, setae could be a model for use in other situations that require maneuvering through tight spaces, such as search and rescue missions. Artificial setae could be used to help a rover move over rough terrain, or to help a rescue worker move through a collapsed building.

AI on AskNature

This page was produced in part with the assistance of AI, which is allowing us to greatly expand the volume of content available on AskNature. All of the content has been reviewed for accuracy and appropriateness by human editors. To provide feedback or to get involved with the project, contact us.

Last Updated August 18, 2016

References

“The basic worm trick consists of stretching and squeezing alternate parts of a long, cylindrical trunk, moving each region of stretch or squeeze rearward, as in figure 24.7a. Despite the rearward progression, the scheme can’t do much without one more component. Thus, a worm on a smooth and lubricated surface makes negligible progress–we’re not looking at an analog of anguilliform (eel-like) swimming. The trunk needs some device so it slides more easily forward than rearward. For earthworms, setae, short rearward-pointing bristles, provide that crucial asymmetry.” (Vogel 2003:488)

Book

Comparative Biomechanics: Life's Physical World, Second Edition

Princeton University Press | 17/06/2013 | Steven Vogel

embedly preview

AskNature