Earthworms: Nature's Composters
By AmosTheCat, 23rd Feb 2012 | Follow this author
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Posted in WikinutGuidesGardeningOrganic
Earthworms are generally regarded as very beneficial to the environment for their role in enriching the soil, but there are some cases in which the earthworm population can bloom out of control and damage the forest floor. This article discusses various interesting features of earthworm anatomy and physiology, and their role in the environment.
- Nature's Composters
- What’s in a Name
- Travel Plans
- Soil In, Soil Out
- Reproduction
- Too Much of a Good Thing
- Buddies For Life
- Edible?
Nature's Composters
Earthworms are one of nature’s most prodigious recyclers, which, with one major exception, is great for everyone. Their digested food contains mostly soil, but mixed with it is dead organic material such as dead leaves. This mixture is deposited on the top of the ground in the form of castings. The castings form a mound around the worm’s burrow and some worms line their burrows with castings. The soil comes from deeper in the ground so the effect is much like a farmer plowing the earth to turn over the soil. However, since the worm has mixed the soil with rich organic material the castings are enriched soil.
Additionally, the burrows become flooded with water during rain, allowing the water and air to penetrate deeper into the soil. This act of aeration also benefits growing plants. For the above reasons many people often mix earthworms (usually red wigglers) with their compost to hasten the composting process and enrich it in the process.
What’s in a Name
Earthworms are members of a very large phylum call annelids, or segmented worms. Non-segmented worms live in water while segmented worms live in soil. Since earthworms live mostly underground they have no eyes or ears. But they have organs in their outer layers of the skin in certain segments that are very sensitive to light (which they avoid) and to vibration. Earthworms must remain moist by secreting mucus through their skin. The earthworm also uses his skin to breathe or exchange chemicals with the world outside his body. The taxonomic class that earthworms belong to is called Oligochaeta, which is Latin for “few bristles”. Tiny bristles called setae, which occur between some segments, aid the earthworm’s burrowing and traveling through burrows.
Travel Plans
To burrow through the soil, the earthworm extends its head end into the soil a short distance, actually eating some of the soil. It then anchors itself there by extending the bristles into the soil around his head end. The bristles in the rest of his body are pulled into its body and, a few segments at a time; it pulls its body forward closer to its head, anchors those segments there with bristles and repeats the process until the whole body has advanced. This may seem excruciating slow, but considering that it is soil it is traveling through, it can actually move quite quickly. If you have ever tried to pull a dew worm (called night crawlers by some) from its burrow or have ever seen a robin try to do the same, the worm may actually break in two before it releases its bristle grip on its buried portion. The robin might devour the dew worm’s back half, but the wily earthworm will generate a new back half and may live to a ripe old age of ten to fifteen years.
Soil In, Soil Out
Earthworm digestion, like the worm itself, is very linear. The mouth opens and takes in whatever is in front of it, usually soil or decaying organic matter. A muscular pharynx moves the food along to the esophagus, which seems to have the function of removing excess calcium from the food. Then the food moves on to a crop where it is stored until the next organ, the gizzard, calls for it. Here the food is ground up by previously swallowed tiny stones. After it is thoroughly ground it passes on to the intestine where digestive juices extract from it the nutrients needed by the body, and passes it on to blood vessels in the intestinal wall. At this time the worm must make a trip to the top of its burrow to deposit the remaining, unused material, made up mostly of dirt. These castings, excreted through its anus, make up the rich piles of dirt, also called a midden, which we find under leaf litter. Although these castings contain rich nutrients, plants cannot use the nutrients efficiently until microorganisms break them down further.
Reproduction
Each earthworm contains the reproductive structures of both genders. Hence they are hermaphrodites. However, since genetics requires the blending of two different sets of DNA, mating with another hermaphroditic worm still must take place. Any earthworm can mate with any other earthworm and they simply exchange semen. From here the process gets very complicated but includes a trip by the unfertilized eggs from one part of the worm’s body to another through a ring of mucous secreted by the worm on the outside of its body. Eventually the eggs get fertilized while inside the mucous ring, and deposited into a cocoon, which the worm slips past its body and deposits into the soil. The cocoon contains nutrient rich albumen, which the developing worms eat until they are large enough and strong enough to break through the cocoon wall into the surrounding soil. From then on they are on their own.
Too Much of a Good Thing
When are earthworms not beneficial? First, when they overpopulate on cool, moist forest floor that has a nice layer of dead leaves and twigs. Second, when there are large populations of them near human homes and help populate the world with cluster flies.
Some Minnesota and Wisconsin forests have a very bad problem of earthworm overpopulation. Geochemists describe forest floors as being made up of horizons. The top-most horizon lies under the latest layer of leaf and twig litter and is known as the O horizon. The O horizon is made up entirely of decayed organic materials from previous years. The decaying of the organic materials making up the O horizon depends heavily upon the moist conditions provided by insulating effect of the leaf litter.
Below the O horizon is the A horizon which is made up of a mixture of organic materials and whatever soil would be there were there no forest at all. The B horizon beneath that is made up entirely of the native soil which is usually rich in clay and minerals. The next layer, the C horizon, is compose of bedrock and the broken up rock debris that appears on the top of bedrock. In rocky areas some of these layers are very thin or nonexistent. In fact, the bedrock will sometimes appear right on the surface in some places (as in our lawn at our cottage).
When earthworms invade the forest floor in great numbers, they begin in the fall eating the forest’s annual offering of dead leaves. But soon the cold drives the worms deep underground where they become dormant for the winter. In spring they begin eating again until by mid to late summer the forest floor can be bare of all litter as well as the entire O horizon. What remains is exposed A horizon with many piles of worm castings scattered about, which in rain becomes a slimy mud field and in hot, dry seasons becomes a baked crust. The lack of cover exposes the B horizon to the sun and wind which dries it out, making it inhospitable to new growth. New fallen seeds, if they germinate at all, die in the next hot spell. The earth is devoid of all new vegetation. Insects, rodents, birds and larger mammals that inhabited the forest are forced out for lack of food or habitat.
How did all this happen in Minnesota and Wisconsin? These northern forests were not originally home for earthworms. In fact, all native earthworms in North America were killed during the last ice age 11,000 years ago. The dew worms and red wigglers we have now are natives of Europe. The thousand (or so) lakes of Minnesota are considered a blessing to that state but the invasion of earthworms is traceable directly from boat launches, lakeshores and ditches. In spite of their slow movement these creatures move inland at a relatively rapid rate and the moisture rich forest floor is a heavenly habitat for them. The practice of many fishermen (including myself) of dumping unused earthworms into the forest seemed not only innocuous but downright beneficial. Maybe not. Some Minnesotan researchers would say, definitely not.
It is fair to ask why earthworms have not invaded forests farther north into Ontario? After all, maple and basswood forest litter is a favorite of earthworms. A study conducted at Bells Corners, west of Ottawa, by Rob Lee found that in spite of many worms in the Macoun Club Study Area forest there was little change in the plant life of the forest floor. Usually more worm resistant exotic species replace native plants, as a first warning sign of worm invasion. Does the Canadian Shield not provide enough soil depth for worms to survive the deep frosts in numbers great enough to support an overpopulation of worms? This and many other possible explanations are under study.
Buddies For Life
Got a cluster fly problem? Then you also have an earthworm problem. Cluster flies lay their eggs in the soil near wormholes. These eggs hatch into larva (maggots) in three days and seek food. They have only one source of nourishment . . . earthworms. Once they find and enter an earthworm they eat for two or three weeks. Then they leave the worm’s to pupate in the soil. Cluster flies, unlike most flies, which prefer your garbage, live on flowers. But in winter they seek the comfort of nice warm places and are particularly good at squeezing through very small cracks. So, even well caulked homes often provide shelter for hundreds of cluster flies. Active manure piles are great places for earthworms to help hatch cluster flies. Even barnyards that were abandoned long ago will produce rich soil in which earthworms will abound; with their buddies the cluster flies.
Edible?
Earthworms are 97% protein. Who could ask for anything more? Click here for a link to a recipe.
Comments
23rd Feb 2012 (#)
They do SUCH a good job of what they do in the cycle of nature ... Too bad people are less suitably adapted to whatever our own role is :-{
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23rd Feb 2012 (#)
Wonderful animals.
They protect this planet.
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23rd Feb 2012 (#)
As they say, too much of a good thing. What a darn interesting article about earthworms. I really enjoyed it. Thank you for sharing.:)
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24th Feb 2012 (#)
Great read, helpful and informative...I love gardening where earthworms rule:0)
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24th Feb 2012 (#)
Great article, Amos. Earthworms have beneficial effects on our planet, unlike Earthlings. Nice to meet you.
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25th Feb 2012 (#)
Thanks to everyone for your compliment on this article. I was doing a little research on worms for our composter and the more I read about them the more I wanted to know. This article is the result.
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25th Apr 2012 (#)
Earthworms are amazing, where would we be without them.
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