Earthworms are seen after rain storms, in the parking lot or on the sidewalks, trying to find their way back to their homes below ground. Sometimes they surprise you when you turn over some old leaves or dig into the compost pile or the garden, and suddenly the shovel has half a dozen lively, wiggly earthworms on board. Many have heard that worms are good for gardens, and it is known that fish value them highly as a food source; so much so that often earthworms are involuntary guests on fishing trips. But do these for the most part unseen creatures have any
buried secrets to share?
Old and new at the same time:
Earthworms are some of the oldest life forms on our planet. Evidence of worms and of their burrows dating back nearly 500 million years, long before dinosaurs or much of anything else walked the earth are routinely discovered in the fossil record. Relatively recent discoveries in India and China indicate that certain primitive worms may have been around as far back as a billion years or more before the present era. This exciting discovery also means that the history of multi cellular life on earth had its origins at least twice as long ago as was previously believed.
So earthworms have been around a very long time, right? Well, yes, and also, no. If you are living in parts of the northern hemisphere like Canada or the northern United States, earthworms only arrived with the first European settlers. The great glaciers formed during the last ice age, which ended about 12,000 years ago freeze-dried and scoured the earth bare of earthworms as they advanced and retreated leaving the remaining soil devoid of most of its multi celled subterranean inhabitants.
Virtually all of the worms living in Canada and the upper USA are descended from relatively recent ancestors that arrived as egg casings trapped in the hoofs of the settler’s horses and shoes, in the ships ballast, or as hitchhikers in the soil used to transport plants from Europe. The spread of earthworms through the vast tracts of land that they currently occupy corresponds with the expansion of European settlement. Present day colonies of earthworms in many northern areas are less than 300 years old.
Tons of earthworms!
Chemical fertilizers can inhibit or even destroy earthworm populations but gardeners who rely heavily on compost and organic soil additives will cultivate an astonishing earthworm population, often unappreciated because it is so rarely noticed. Illinois scientists did a study in 1997 as part of a project called “The Illinois Soil Quality Initiative” that involved taking samples from 12 different farms with similar soil characteristics and also from the unfarmed – and therefore unfertilized - grassy borders of those fields.
They found that on average, an acre of conventionally farmed cornfield contains around 148,000 earthworms, translating to 78 pounds of living worms. The field with the richest population density hosted 292,000 worms, or nearly 180 pounds of living weight. To everyone’s surprise, the richest sample came from one of the unfarmed grassy borders. Sampling revealed a population of 1,540,000 per acre, or a whopping 5909 pounds – nearly 3 tons – of earthworms! The great weight disparity between the two types of samples is explained by the fact that not only was there more worms in the grassy borders of the fields; the individual worms themselves were much larger.
But this is really nothing compared to the fertile Nile Valley of Egypt, where samples have topped 2,500,000 worms per acre during the growing season, or of a sample drawn from an especially fertile field in New Zealand, where research uncovered an astonishing 4,000,000 earthworms per acre, or a live weight of 15,000 pounds – seven and one half tons - of completely unseen sub surface worm life!
To put this in perspective, if one were to fence off an acre of that New Zealand pasture and temporarily pen 5 large cows, each weighing 1500 pounds inside, there would be twice their weight in living worms underneath the grass on which they grazed.
Our unseen gardening friends:
Earth worms do much more than just set underground weight records; they are the organic gardener’s best pals. Each day earthworms eat a mixed dinner of organic material, soil and sand particles, anywhere from half of their own bodyweight to an amount equal to their weight. They process - digest - this material and excrete the remainder in the form of water soluble pellets called castings. These castings, as it turns out, are the perfect fertilizer for the plants humans like to grow. The castings present the plants with 5 times the concentration of absorbable nitrogen, 7 times the phosphates and 11 times the potash – not to mention trace nutrients – than is present in the organic matter which the earthworms consumed.
Henry Hopp, researcher for the United States Department of Agriculture states that just an average acre of agricultural land housing only an average worm population can generate 5 tons of these organic plant nutrients per year. Best of all this gentle, effective fertilizer is delivered directly to plant roots in precisely the correct form for optimal absorption.
While the worm is enjoying dinner he is constantly burrowing through the soil, opening passageways for air and water to pass through and for the roots of the plant to grow into. When you are working in your garden, you are never working alone. There is a volunteer army of agricultural experts toiling just beneath your feet.
The long and the short of it:
Earth worms come in many sizes; turn over that compost heap and you may find little half inch long wigglers and mighty night crawlers stretching 8 inches or more in length. But visit the Beatrix Gold Mine in South Africa as a group of scientists recently did and you may find colonies of Halicephalobus mephisto, not a true earthworm but a deep dwelling nematode cousin, that is a mere half millimeter in length. It would take 50 of these tiny creatures placed end to end to add up to one inch.
And these are tough little worms indeed, dwelling in world where temperature may reach 100 degrees and more, where there is little oxygen and the only food available are single celled bacteria that live in minute cracks in the rock.
As with the ancient worms found in China, these deep dwellers - DNA from as yet unnamed nematodes have been found 2 ¼ miles down - are pushing back the boundaries of our knowledge of multi cellular life forms. Prior to their discovery science was reasonably certain that only a few very robust strains of single cell bacteria could exist in the hostile environment that prevail at such depths.
At the other end of the spectrum, meet Megascolides Australis, a rare earthworm from a very restricted range in Australia, which averages three full feet in length but can occasionally grow to as long as ten feet. This interesting worm needs very wet soil to survive, and even though it cannot be seen it can frequently be heard as it squishes and gurgles its way through its damp burrows.
And yet, Megascolides is a lightweight compared to the mighty Giant South African Earthworm, which averages six feet in length but has been recorded to reach an almost unbelievable 20 feet in the case of a few extremely old and presumably well fed specimens.
The United States hosts the rare Oregon worm, which can attain several feet in length but whose real claim to fame lies in the aroma of lilies that it exudes when handled. New Zealand, far from being outdone presents us with the Auckland worm, large, incandescent blue by day and throwing off a cold light not unlike that of a firefly at night. It is claimed that just a few of these worms provide sufficient light to read by.
No, it turns out that the common earthworm, bless its heart, is not as common as is generally thought. Or perhaps one should say “bless its hearts” because most earthworms, who have no lungs and must breath through their skins, pump the resulting oxygenated blood around their bodies using five sets of double hearts based in segments located just behind their heads.
But stay tuned, folks, because it is not to be thought that science has yet uncovered all of the amazing secrets of this commonplace, but not at all ordinary, creature.
Well there you have it kids, everything you will ever need to know about earthworms and then some! As always, thanks for spending an hour or so with Leatherface!