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Earthworms

John Mertus

1993

by John Mertus

I've been following with interest the thread on using worms to eat the garbage. Since there seems to be interest in earthworms, I am re-posting a combination of three posts from one to two years ago. I live in the Northeast so most of this is about earthworms of this area; the South and Southwest are different.

As gardeners we have all come to love the earthworm and want our soil to hold as many as possible. I'm a firm believer that understanding the earthworm means we can understand how to help keep them. There are over 3,000 species of earthworms, but only a half dozen or so are important to cultivation.

If you dig in typical northeast garden soil, you are likely to find three different types of worms. The canonical night crawler, the common field worm and the green worm.

The new world did not have any of these worms before the Europeans. The worms were inadvertently brought over in pots and spread throughout the Northern American soil. We often think that foreign fauna as bad, witness the Japanese beetle or Gypsy moth; but the earthworm is an import, and our soils and gardens would be so much more poorer with it.

The night crawler, Lumbricus terrestis, is the largest and likes soils that are heavy in organic matter like lawns and meadows. When the soil becomes poorer, the common field worm, Allolobophora caliginosa, and all its variants become more common. This is a smaller worm with a pronounced raised band, called the clitellum, about 1/4 of the way down its body. Both these worms are quite active and feed by bringing down organic debris in to their borrows from the surface, their holes aerate the soil and their excretions, called casts, improve the friability of the soil. The last common worm is called the green worm, Allolobophora chlorotica, which is a stout greenish colored worm that is quite dormant and does little to improve the soil.

Figure 1. Common Earthworms

Common Earthworms
From top to bottom: Night crawler, Field Worm, manure worm, and green
worm.

The very active red wriggler, or manure worm, can be found in compost piles. You know you have a red wiggler when you pick it up: it thrashes about, wiggling and squirming. The true red wiggler, Eisenia foetida, has alternating bands of yellow and maroon down the length of its body. A similar worm, Lumbricus rubellus, is a deep maroon color without the yellow bands.

These manure worms need extremely high organic matter, such as manure or rich kitchen scraps to survive. Manure worms just cannot live in common garden or lawn soil. (Unless the soil is very very rich.) So when you shovel your red wigglers from your compost pile into the garden, you are dooming these guys to provide nitrogen for your plants by their bodies.

But the life of an earthworm in general is hard. Their bodies are about 70% protein; rich food for many predators. Their major enemies are insect eating birds, like robins, and mammals like moles. If you watch a robin hunting, it pauses, cocks it head and then hops. The robins ears can actually hear the earthworm moving under ground. But the earthworm, although sightless and ear-less can feel the vibrations of the bird on the surface. It's the deadly game of survival.

Another major earthworm predator is the mole. This voracious insect predator loves to dine on white grubs and any earthworm it can find. Grubs, attached to the root from which they gain their food, can't escape, but the earthworm can feel the vibrations of the mole digging and quickly try to flee. The moles own digging conceals the noise of the earthworm fleeing, so the star nose mole developed a unique method to find earthworms. It uses its funny looking nose to detect the faint electrical fields that earthworms (and some other insects) radiate. Not only does this mole detect and find an earthworm, but it knows how to bite it so it is paralyzed but does not die. The mole stores the living worm along the burrow as food for dining at leisure. Once again, nature ain't nice!

Another predator, usually not found in the northeast, is a carnivorous snail. These snails are long and thin, just right for invading the shell of another snail and devouring it. But they also love earthworms.

When you till the ground, the earthworms flee the tillers vibration. (They must think it's a really big mole.) So the active earthworms are not usually chopped by the tiller. Some earthworms, like night crawlers, have 5 hearts. If chopped in half, they don't die but try to regenerate; however, sometimes a half gets confused and it end up regenerating a worm with two heads or two tails.

Tilling the soil does reduce the earthworm population. Not because it kills or disturbs them, but because tilling aerates the soil, and this oxygen quickly reduces the organic matter that the earthworm uses as food. Mulching with green matter will help provide food to earthworms to replenish what is lost in tilling.

The population of earthworms, in the north, follows a different cycle then most garden fauna. The population of adults is highest in the spring, and decreases in the dry summer months, followed by a increase of young in the wetter, cooler fall. In the hot dry months of July and August, you often don't find many earthworms. For a high number of earthworms in the spring, it's important to protect the young and the eggs over winter.

Earthworms can freeze solid and still live if the freeze is slow and they do not thaw out and refreeze often. Any form of ground cover, cover crops, leaves, mulch or even boards help mediate the freezing and allow more earthworms to survive the winter. Fields that are plowed and left bare are almost devoid of earthworms in the spring. Luckily, earthworms have a high K (reproduction) factor.

Earthworms are hermaphrodites with both male and female organs. They mate by lying head to tail with each worm producing a temporary skin canal through which the sperm flows into each other to be stored in a sperm sack. The girdle like ring around the front of an earthworm, called the clitellum, later slides along the worm and picks up the mature eggs and sperm. It falls off the worm and the combination tube, egg, sperm and mucous form a well protected nest for the worm eggs.

It's quite amazing to watch earthworms “do it”, how they form almost into one body, incredibly long and slimy, and then break away each darting back into its own hole. (To chew on some tobacco leaves I suppose.)

One of the major myths, reported by many otherwise informed authors, is that earthworms come out of their burrows during a rain to avoid drowning. Worms have no lungs, they take their oxygen directly thorough the skin, either from air or from water. In fact, rather then fear water, they love it. It's drying out they fear and dry soil kills them. When it rains, they come to the surface because it's easier to find a mate in the flat open ground then in the three dimensional burrows. The wet ground allows them to move without fear of drying out. To an earthworm, the wet ground is a wild singles bar.

Earthworms use lots of water since they produce 60% of their body weight in urine every day. Urea is very high in nitrogen and provides an excellent fertilizer. The worms in a field easily produce about 50 lbs nitrogen/acre, which is the same amount of nitrogen that a crop of hay takes out of an acre! The earthworm casts of contain concentrated nitrate, phosphorous, exchangeable magnesium, potassium and calcium. All essential to plant growth. The organic material bound to earthworms and other soil dwellers is about 1 ton/acre which is released gradually as they die in the dry summer, providing a great nutrient reservoir for our plants.

As a society, we are so use to going out and purchase what we need to solve our problems: need to chop vegetables quickly? Buy a food processor. Need to water the garden easily? Buy a drip system and an automatic timer. It is so tempting to do the same for insects: need to eliminate some grasshoppers? Buy some praying mantises. No worms in your soil, buy some earthworms. Gardening just doesn't work like that. You must provide conditions for the worms to flourish.

Earthworm populations are limited by the amount of organic matter, water and survival over the winter. To grow a good earthworm crop, feed the soil. The ultimate factor limiting worm population is usually food and water! Night crawlers have been kept alive for 10 years but in the garden their life span is usually no more then one year, maybe two. It's necessary to ensure the eggs and young survive the winters.

That's what organic gardening always comes back to: feeding the soil and the rest takes care of itself. Earthworms need organic debris and mineral soil for food. The use of artificial fertilizers, be they chemical or organic, do not provide the necessary food for earthworms. Neither do dry leaves. Before they fall, the tree sucks out all the essential chemicals it can and leaves a leaf that has almost no nitrogen in it. At least, not enough for the earthworm to eat and survive. Grass clipping, corn stalks, green leaves, and for me the maple whirlly birds, provide good sources.

So when you dig up a worm, realize it is all part of a wonderful cycle, its life improves the soil, its wastes add great fertilizer, and even in death, the worms body contributes its nitrogen at a time when nitrogen may be becoming scare.

While the author's home page is still available on the web, this page was no longer available at the time of preparation. As an archival document, we have limited the scope of our changes to minor spelling and punctuation corrections.


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