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Earthworm photo


Earthworms are a good thing. They are like natural aerators/fertilizers of our soil. In fact Aristotle called them the "intestines of the earth." Earthworms are important soil organisms that aid in the decomposition of plant litter, such as the thatch layer, and in recycling of nutrients.

One important thing that earthworms do is to plow the soil by tunneling through it. Their tunnels provide the soil with passageways through which air and water can circulate, and that's important because soil microorganisms and plant roots need air and water items as much as we do. Without some kind of plowing, soil becomes compacted, air and water can't circulate in it, and plant roots can't penetrate it.

Earthworms are generally found in the top 12" to 18" of the soil because this is where there most abundant food source is located. The worm ingests soil and organic matter which is swallowed and ground in the gizzard. The ejected material, castings, are used to line the burrow or are deposited at the entrance. Earthworm activity depends directly on soil moisture and temperature. They become active when soil thaws in the spring and move deeper in late summer as the soil dries.

Earthworms are also nighttime scavengers, emerging from their burrows looking for organic matter to store inside of their burrows for future use.

Some earthworm facts:

  • An earthworm can grow only so long. A well-fed adult will depend on what kind of worm it is, how many segments it has, how old it is and how well fed it is.

  • Worms can eat their weight each day.

  • An earthworm has no arms, legs or eyes.

  • There are over 2,500 different kinds of earthworms.

  • Worms can live wherever they can find food, moisture, oxygen and a favorable temperature.

  • There are about a million earthworms in one acre of land.

  • The largest earthworm was found in South Africa and measured 22 feet.

  • Worms tunnel deeply in the soil and bring subsoil closer to the surface mixing it with the topsoil. The sticky slime found on an earthworms skin, helps hold clusters of soil particles together in formations called aggregates. This slime is actually a secretion from the worm and contains nitrogen.

  • Worms are cold-blooded animals.

  • Worms can grow a new tail, but not grow a new head if they are cut off.

  • Baby worms hatch from cocoons smaller than a grain of rice.

  • Earthworms don’t have eyes, but can sense light, especially at their anterior (front end). They move away from light. If exposed to light for about an hour, they will become paralyzed.

  • If a worm’s skin dries out, it will die.

  • Worms are hermaphrodites. Each worm has both male and female organs. Worms mate by joining their clitella (swollen area near the head of a mature worm) and exchanging sperm. Then each worm forms an egg capsule in its clitellum.

Inadvertent casualties

With the advent of chemical pest control, however, earthworms have become non-target recipients of many pesticides. Some of the most effective pesticides are broad spectrum in action, and they may inadvertently harm earthworms and other beneficial soil organisms. Harmful substances ingested by earthworms also may be concentrated up the food chain.

How earthworms travel

Earthworms have no bones, but they do have a system of muscles that enable them to wiggle, contract and expand. Their body also has small, almost invisible bristles (known as setae) which they can rise and lower in different sections of its body. When collapsed, the earthworm can easily slide along, however, when raised, the setae dig into the surrounding dirt. This comes in handy if a bird nabs a worm's head and tries to pull the worm from its burrow. The setae anchor the worm so well that it may break before coming out.

Movement is accomplished by the earthworm first raising the rear section of setae to anchor its tail against the tunnel wall. Then using its muscles, the earthworm stretches itself forward. It then raises its setae near its head and lowers its tail end set of setae, then contracts its body pulling it forward. It continues this process of stretching, anchoring, and contracting to move along its tunnel.

How earthworms breathe

Earthworms don't have lungs, but instead breathe through their skin. In order for air exchange to take place, the outermost layers of an earthworm are thin and must be kept moist to remain effective. The slime excreted onto the skin keeps it moist. It is also wet by body fluid which is excreted through 'dorsal pores' located along the dorsal (back) midline in the grooves between the segments.

This need for moisture restricts an earthworm's activities to a burrowing life in damp soil. They emerge only at night when the evaporating potential of the air is low, and retreat deep underground during hot, dry weather. Light-sensitive tissues near the worm's head enable it to detect light, so they can avoid venturing out by day.

Earthworms and Weeds

Recent research by the Ohio State University was recently published in the Journal of Applied Ecology, describes research that earthworms feed on decaying organic matter. While this is not too surprising, what is surprising is that they store organic matter deep in the ground that then begins the decaying process providing them rich nutrients deep in the soil. The seed of choice for the earthworms is the large ragweed seed.

During the growing season a weed will produce 1000s of seeds. Most of those seeds fall to the ground where they are eaten by birds, rodents and other insects. This usually ends the life-cycle of the seed, but in some cases, the night-scavenging earthworm finds some of the seeds and takes them into their burrow where they are buried. The seeds are then stored about 2" below the surface. Most seeds will eventually decay providing the earthworms valuable nutrients, but given the right conditions, some of those seeds may also germinate.

In the study by Ohio State University, it was determined that on average a farm field might contain 3 - 4 earthworms per square foot. In areas where ragweed was common, there might also be about 500 ragweed seeds and from those 500 seeds, some 300 could emerge into adult plants which creates an extremely difficult problem for farmers. In fields where ragweed is left to develop, it's aggressive growth can reduce corn and soybean yields by as much as 75 percent.