THE EARTHWORM IS A SPECIAL SORT OF WORM. Almost alone among his brethren, he does not inspire horror. In fact, the earthworm is almost alone among all the invertebrates in the tenderness he inspires. Knowing that a worm in the sun is as good as dead—since his skin has no defense against desiccation—children often place him gently in the shadow of a log or cover him with a light handful of soil. And gardeners, above all, venerate the worm.
The earthworm has also inspired an unusual quantity of study. Charles Darwin, who spent the better part of his time conceiving The Origin of Species, devoted a whole volume to the worm. In his The Formation of Vegetable Mould through the Action of Worms (1896), a classic of soil ecology and a charming book, Darwin not only summarized all the knowledge then current on earthworms but also reported on his own experiments with exposing worms to light and heat. It was his delight to have friends send him interestingly shaped worm castings from around the world. In his concluding chapter, he begins, “Worms have played a more important part in the history of the world than most persons would at first suppose.”
Indeed. Though Darwin’s own notions regarding the primary importance of worms in the creation of humus leave out the very important influence of the microbial population, it nevertheless points in the right direction. A healthy population of earthworms is the sign and partly the cause of a healthy soil.
When worms are happy, there are lots of them. In a Danish forest soil, researchers have found a density of one million to one and a half million worms per acre, more than two tons of worms. A rich grassland may bring up more than five hundred worms out of a square-meter hole. This is not so remarkable when you recognize that eight relatively healthy worms will produce fifteen hundred offspring in half a year’s time.
There can even be too many. George Perkins Marsh, writing in the mid-nineteenth century, reported a conversation with an elderly New England pioneer who in her girlhood had witnessed the rise of worms in that part of the world. The common earthworm is not native to America, having been brought over by colonists. When it first appeared, it was not numerous, she reported. But as fields were cleared, its numbers increased to such a degree the water of springs and wells was polluted by the number of dead worms in it. Only the corresponding introduction and increase of robins and other vermivores corrected the imbalance.
Nevertheless, the presence of earthworms is by and large a very good thing for the soil. Unlike a given fertilizer, for example, it acts simultaneously on several different soil parameters.
Worms are basically blind. They see by eating. Darwin tried in vain to scare his worms with a light, but he found that they would only withdraw into the burrows if the light were a hot one. Heat/cold and wet/dry are the polarities that matter to worms. Both are meant to keep them at the optimum lubriciousness for ingesting and passing soil through their bodies.
A worm is a long intestine. Soil, rich in dead organic matter, leaves, and especially manure, goes in one end and comes out the other, concentrated, enriched, and well mixed, in the form of “castings.” A well-manured soil is almost always rich in worms. Up to ten tons of worm castings per acre per year enrich a soil under favorable conditions. The worm also senses and creates the topsoil in a very basic way: by going where the organic matter is, mixing it, and excreting it behind or above him. Worms also bore down to the water table, but not into it. At the dry surface, too, they stop. More than any other creature, the worm defines topsoil.
Some leave their castings on the surface, others in the body of the soil, but in any case, the leavings have several virtues. For one thing, they concentrate nutrients. Scientists estimate that worm castings contain five times more nitrogen, seven times more available phosphorus, eleven times more potash, and forty percent more humus than usually is to be found in the top six inches of soil. For another thing, the castings mix the soil ingredients, facilitating their further breakdown by microbes. This has been proved in an ingenious experiment, ironically enough using carbon-14 laid down by successive nuclear tests as a measure.
The earthworm is also a pathfinder. It might be said that he weaves the soil with the thread of his leavings but also with the underground channels he creates. His blindness does not hinder his motion. A single acre of cultivated soil has been seen to have more than six million worm channels, whose presence significantly increases the soil’s ability to hold and percolate water. A clayey orchard soil had more than two million large channels (some as thick as your little finger) in an acre, the equivalent, experimenters reported, of a two-inch drainage pipe. Other investigators have found that down to a depth of four inches, up to fifty percent of the soil’s air capacity consists of the tunnels and cavities dug by worms.
Fishermen, who have a periodic and urgent need for the reclusive night crawler, have elaborated particular methods for coaxing him from the soil. Some say that they will come up if you pound on the ground, because they mistake your fists for rain. I bet. But the best way to catch worms is to “telephone” them.
The technique is named for the old-fashioned hand-crank generators that resemble old telephones. In fact, any generator or even a car battery will do. When an electrode is stuck into the ground, the night crawlers come directly to the surface. Why? “You would too,” says Sybil Wallingham of the Wallingham Worm and Rabbit Farm in Butler, Georgia. “It’s the same as if you’re standing on wet concrete when the drill shorts out.”
Soils, particularly when wet, are fairly good conductors of electricity. The worms’ sensitivity to the charge is exquisite. In fact, they are markers of most calamities that happen in the soil. When a soil is too wet, the worms come to the surface. Just before an earthquake, too, they will often be found aboveground. Worms are the watchmen of the soil.
To encourage earthworms to live in your soil, provide them with plenty of organic matter. Professor Daniel Dindal of Syracuse University, an expert on soil organisms, suggests adding either a compost made from autumn leaves and manure, or freshly mulched leaves worked directly into the soil with a pitchfork and a hoe. Dindal also recommends adding a sprinkling of ground eggshells or other calcium-rich materials, since worms concentrate calcium in their guts and excrete it into the ground, where it can help to neutralize acid soils.
Is there nothing more arcane that needs to be done? “No,” says Dindal, “just break up the materials so they are bite-sized for a worm.”
There is no end of places where the gardener can buy worms, but there is seldom a need to, unless you are starting worm composting. Generally speaking, if you build soil, worms will come.