The Fascinating World of  Worms

BY AWAKE! WRITER IN AUSTRALIA

QUEEN CLEOPATRA of Egypt declared them sacred. Aristotle called them the intestines of the earth. Charles Darwin felt that they played an important part in the history of the world. What animal earned the admiration of such famous people? The humble earthworm.

As you will see, worms deserve to be admired. True, they are slimy and they wriggle. But even these qualities, which we might consider unattractive, can inspire a sense of awe once you get to know the worm a little better. All you need to do is bend down and upturn a clod of soil or disturb a layer of leaf litter, and you have entered the fascinating world of worms.

Simple Brain, Astounding Talents

Take a closer look at an earthworm, and you will notice that its body is constructed of ringed segments that look like a row of miniature doughnuts bunched tightly together. Each segment is powered by two groups of muscles. One group, just below the skin, forms a ring around the worm. Beneath this layer, the second group stretches along the worm. The worm moves by expanding and contracting these opposing muscle groups, flexing segment after segment in a rhythmic pulse that ripples down its body.

If you place an earthworm in your hand, no doubt it will writhe and wriggle. The worm reacts this way because its body is bristling with sense organs​—as many as 1,900 on just one segment. These receptors give the worm a sense of touch, the capacity to taste, and the ability to detect light.

The worm grips the soil with the aid of small, hairlike projections called setae. Each segment of the worm has sets of setae that act somewhat like the oars of a rowboat. The worm plunges them into the soil, pulls itself along, and then retracts them. The worm can “paddle” in either direction using one set of setae at a time or, if startled, can anchor one end of its body while rapidly retracting the other end. The athletic skill displayed in timing these “oar strokes” would make an Olympic rowing team envious.

If a bird nips off a worm’s tail segments, some species of worms simply regrow them​—but they never regrow more segments than are lost. It seems that each segment generates a tiny electrical charge and that worms regrow lost segments until a preset maximum charge is regained.

The thousands of sense organs and the complex muscle systems are all wired into the cerebral ganglion, located at the mouth end of the worm. Experiments have shown that in addition to their physical talents, worms have a limited capacity for memory and can even learn to avoid danger.

Why So Slimy?

The slimy surface of the worm, which many find so revolting, actually allows the little creature to breathe. The worm’s skin is porous, and blood vessels close to the skin absorb oxygen from the air or from oxygenated water while releasing carbon dioxide. But these gases can interchange only if the skin is moist. If a worm dries out, it will slowly choke to death.

On the other hand, if a worm is trapped in its burrow during heavy rain, the oxygen supply in the water will be quickly exhausted. This is one reason why worms crawl to the surface after a downpour. If they don’t evacuate, they will suffocate.

A Planet Crawling With Productive Plowmen

Over 1,800 species of earthworms share our planet. They inhabit all but the driest and coldest parts of the earth. Under the savannas of South Africa, there may be as few as 7 worms in every square foot [70 worms in every square meter] of soil, while on a forest floor in Canada, there may be over 70 worms per square foot [700 worms per square meter].

In New Zealand, earthworms are divided into three basic types. The first type contains fast-breeding, fast-moving worms that live among rotting organic matter on top of the earth. The second and most widely distributed type consists of worms that burrow horizontally through the top layers of soil. Worms of the third type bore vertically into the ground and may spend several years​—a worm’s entire life span—​in one burrow. These are the musclemen of the worm world. They have powerful rings of muscles around their heads that enable them to push and chew their way into the earth. One of the largest worms in the world is found in southern Australia. This giant may grow to over four feet [1.5 m] in length and weigh a pound [500g].

As worms squirm through the earth’s surface, they act like miniature plowmen. Munching their way through manure, soil,  and decaying vegetation, they produce a waste product called worm castings​—a product they manufacture in enormous quantities. It has been estimated that worms working under the green fields of England annually churn out about eight tons of castings per acre [20 tons of castings per hectare]. More impressive are the worms that inhabit the Nile Valley. These worms may deposit up to 1,000 tons of castings per acre [2,500 tons of castings per hectare]. As worms till the soil, it becomes better aerated and more water absorbent and increases in fertility.

Scientists have discovered that the worm’s digestive system converts nutrients into forms that plants can absorb, so worm castings are bursting with plant food. In addition, many harmful microorganisms found in rotting manure and vegetation are destroyed as they pass through a worm’s gut. Thus, worms clean the soil as they feed. An ideal recycling machine, they thrive on waste while manufacturing nutritious food.

Harnessing Worm Power

The worm’s remarkable recycling powers are being harnessed by the waste-disposal industry. One company in Australia makes use of a total of 500 million worms in several waste-processing plants. The worms are housed in specially designed beds and are served a menu of either pig manure or human waste mixed with shredded wastepaper and other organic matter. These worms consume between 50 and 100 percent of their own body weight each day and produce a nutrient-rich plant food that is marketed widely.

Studies have revealed another possible use for worms​—as a source of food. Worms contain the same beneficial amino acids as beef. On a dry weight basis, they are packed with 60 percent protein and 10 percent fat and contain calcium and phosphorus. Already, in some lands, people eat earthworm pies. In other parts of the world, they fry earthworms and even eat them raw.

While worms may never become the most popular animals in the world, the world would certainly be a different place without them. So the next time you admire a tranquil country scene, spare a thought for the army of earthworms that are beneath your feet, busily plowing, fertilizing, and maintaining that beautiful view.

[Diagram/Pictures on page 22]

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The Anatomy of an Earthworm

Epidermis

Longitudinal muscle

Setae muscle

Setae

Circular muscle

Bladder

Intestine

Nerve cord

[Credit Lines]

Lydekker

J. Soucie © BIODIDAC

[Picture on page 20]

Worms “paddle” through the soil with their setae

[Picture on page 21]

Worms till the soil, increasing its fertility

[Picture on page 21]

The giant Gippsland worm, an endangered species in Australia, can grow to over four feet [1.5 m] in length

[Credit Line]

Courtesy Dr A. L. Yen

[Picture on page 22]

Worms convert waste into nutrient-rich plant food