Field Notes–

The Way Of The Worm

By Curtiss Clark

On the earthworm’s calendar, this is the time of year that gardeners start digging down from above and bob-bob-bobbin’ robins drop in at the worm hole for dinner — to eat the host. Life at the surface gets about as breathless as it can be for a creature without lungs.

Nevertheless, the earthworms are surfacing. Spring showers have coaxed them out of the ground, and the gardeners and robins are overjoyed to see them.

The damp days before the summer sun starts to bake the landscape allow earthworms to move around more easily above ground. Since they breathe directly through their skin, their outer membranes need to stay moist and porous; if they dry out, they suffocate. If you’re an earthworm blindly searching for a mate (that’s right, they don’t have eyes either), you’re chances of getting lucky are a lot better above ground than down in your tiny isolated tunnel.

The lowly life of the earthworm doesn’t look like much from our exalted perspective. It crawls through the dirt, a blind, slimy tube of tissue with openings at each end: rotting organic material in, poop out. It’s pretty basic — basic to all of life, that is.

Charles Darwin, who new a few things about the hierarchy of species, made this observation about earthworms in 1881: “It may be doubted whether there are many other creatures which have played so important a part in the history of the world.”

That’s a pretty sweeping statement to come from a scientist as exacting in his observations as Darwin, but after studying worms he was duly impressed. He estimated that a typical acre of cropland contains up to 53,000 earthworms. From that estimate, he calculated that in ten years the worms in one acre of arable land would produce enough castings (what you call worm poop in polite company) to cover that acre at a depth of two inches. Being a prodigious excreter doesn’t always buy you a lot of influence in the world, but when your, ahem, castings are as rich in nitrogen, calcium, magnesium, and phosphorous as an earthworm’s, you occupy a place of prime importance in the earth’s ecosystem.

By distributing this perfectly balanced mix of plant nutrients and minerals as it moves on and through the ground, the earthworm aerates and enriches the soil, making it possible for flora to flourish where it would otherwise fail.

Earthworms literally underlie the food chain not only for herbivores but for carnivores as well. Hedgehogs and moles relish an earthworm snack, and for good reason; they are 70 percent protein.

As we all know, robins are particularly fond of earthworms. This time of year, robins take up positions all over the yard, hungry and ready to play with their food. Tug-of-war is the game of choice, and the robin assigns to the earthworm the roles of both opponent and rope.

So why, if the earthworm is so slippery and smooth, does the robin have such a struggle in tugging it out of the ground?

It has to do with a little trick of earthworm anatomy that helps it go when it wants to go and stop when it wants to stop. If you have ever watched a worm dig for cover after being unearthed in the garden, you have noticed that it moves through a series of waves of muscular contractions along its many segments. It is elastic and lengthens and contracts different parts of its body. The lengthened parts get skinny, and the contracted parts get fat. The short and fat segments in this process squeeze out nearly invisible bristles, called setae, which anchor the worm at that spot, so it doesn’t slip backwards in all the undulating. That’s also how they grip the ground when the robin comes calling.

While they appear to have all the complexity of spaghetti, earthworms have lots of bells and whistles other creatures don’t. Surprisingly, they represent the median of all animal life forms when it comes to complexity. About half of our planet’s creatures are more complex and half are less complex.

It’s a safe bet, however, that few creatures have a love life as complex as the earthworm’s. They are hermaphrodites, having both male and female reproductive organs, but they aren’t designed to fertilize their own eggs. The mating ritual requires each partner to line up his/her male parts with his/her mate’s female parts for a little quid pro quo. Then the worms head off on their own to create a cocoon into which they deposit their own eggs and their partner’s collected sperm. They then can face the summer knowing that if they dry up in the summer sun or lose the tug-of-war with the robin, a new generation will emerge beneath the cool damp leaf litter in the fall.

The whole complicated process seems to be more of a business transaction than a romance. I guess that’s just the way of the worm. No eyes, no eye contact.

Still, I would expect a little more passion from earthworms. Did I mention that they have five hearts?