The Humble Earthworm: Surprising & Amazing

Considering they have two brains, five hearts, are incredibly strong, resilient and fertile, these little invertebrates are nowhere near as simple as they appear. They are among the most ancient life forms on the planet and still as relevant today as when they first appeared. There’s quite a lot to them.

How Old Are Earthworms?             

Earthworms are incredibly ancient. They first appeared half a BILLION years ago. They were part of the “Cambrian Explosion,” a brief period when all the major animal groups first appeared. Of course, having
no bones, worms don’t leave a lot of fossils. But in rare instances of unusual preservation, they have been found. Most of the worms from this time, naturally, are extinct. But, amazingly, there is one still alive today.

As they eat and poop their way through the soil, worms actually help create the ideal conditions for Life. They aerate and fertilize the soil, turning over vast amounts of it, and leaving it in better
condition than when they found it.

How Much Soil Do Worms Actually Move?

It’s estimated that, over the course of a year, on only one acre, earthworms move eight tons of earth. That would be a full load for the average dump truck, give or take.

But they don’t just move, aerate and overturn the soil, they make make more of it. About two inches worth a year. They leave their nitrogen, phosphorous and calcium rich castings up on the surface, causing the previous surface to slowly submerge. They keep doing it, and it keeps mixing down, in a constant ever-moving renewal.

Worms are Surprisingly Strong

They have to be. In order to be able to move through the dirt, they need to forcefully enlarge tiny gaps and crevices. This is a lot of weight to push against. But full grown worms can push ten times their own weight. And baby earthworms are even stronger. They can push five hundred times their own weight.

Being totally voracious, they eat their own weight, everyday. Maybe that doesn’t sound like much, seeing as they aren’t that big. But in that same one acre of land, assuming it has relatively healthy soil, there can be more than a million earthworms.

With that much strength and that much eating, in those kinds of numbers, it’s no wonder they are such incredible earth-movers.

How Many Types of Worms Are There?

Today, there are about 2,700 different worm species, as far as anybody knows. (There’s probably more.) They live where ever they can find food, moisture, oxygen and a comfortable temperature. Being cold-blooded, temperature regulation is important. Different species
burrow to different depths, so the more diversity, as far as plant health goes, the better.

How Big Can Worms Get?

Every species has a size limitation. They don’t get extra enormous, for having extra space or food, the way some fish do. But there are some really large species of worms. There was one, for example, in South Africa, the biggest ever, that was 22 feet long! The adult Australian Gippsland worm can grow to 12 feet long, weighing in at1.5 pounds.

Can Worms See, Hear and Smell?   

Worms don’t have eyes, so they cannot see. But they can sense light. They sense it more strongly from their front end, in order to move away from it. Because if exposed to light for more than an hour or so, they’ll become paralyzed. And, if their skin dries out, they’ll die.

They sense sound vibrations, too, without having ears. Charles Darwin discovered this by putting them in a pot of soil on his piano. As with every species, there is a strong evolutionary imperative to avoid the vibrations of predators, like underground moles, for example.

They do not have a nose, so they cannot smell in the way we think of it. But their nervous system is connected to a series of sensitive chemo-receptors, with olfactory hairs, on their skin. With these they are either attracted to or repulsed by the substances they come into contact with. This tells them to move toward or away, as need be.

Worms Don’t Have Teeth. How Do They Eat?

They have a gizzard. They pull food into their mouth with the small first segment of their body. This is called the prostomium. Then a muscular pharynx sucks it into a crop, where it’s stored before getting ground up in the gizzard. Birds have gizzards, too. It’s a specialized stomach that uses sand or grit to break down and digest food.

After that, the small intestine absorbs the nutrients into the body, and the rest is pooped out the end.

They are very efficient eaters and poopers. Both taking in and putting out their weight in a day. Boggles the mind, doesn’t it?

What a worm eats depends on their species and where they live.

Basically, there are three types. The surface dwellers, the upper soil worms and the deep burrowing worms. Also known as Epigeic, Endogeic and Anecic, respectively.

The upper two types eat dead and decaying animals and plants. Not directly, however, as their mouths are too small. It’s kind of like they eat the decay. Millions of microscopic soil organisms start the digestion process, and the worms eat these miniscule algae, bacterium and fungi along with their bi-products.

The deep burrowing species basically eat dirt, but of course this contains microscopic soil organisms, as well.

Mmm! Delicious!

But
to them, it is.

And it makes the Living Soil a literal paradise for
the plants that get to grow there.

How Do Worms Reproduce?

Worms are hermaphrodites, meaning each has both male and female reproductive organs. That lighter colored swollen band near their head is their clitellum, which is where sexually mature worms, exchange sperm. But it still takes two. They cannot impregnate themselves. Diversity in the gene pool is important.

As is a good courtship ritual. Worms do not just have anonymous sex. Prospective mates visit each other, repeatedly, in their respective burrows. My place today, yours tomorrow. Sometimes, it only takes a couple visits. Other times, it takes a lot. They could go back and forth ten or twenty times. Maybe their chemo-receptors need to get in sync first, and that just takes however long it takes…

Whatever their requirements, once they’re ready to mate   they lie next to each other, head to tail, in a tight bond. Their clitella (plural for clitellum) secrete a mucus film, that envelopes the couple. They’ll stay stuck to each other like this for a few hours, each receiving sperm from the other, which they store for later.

Each leaves the encounter, freshly fertilized.

After this, their clitellum will secrete a substance, albumin, which hardens it. As the worm wriggles out of her/his clitellum, she/he deposits her/his eggs into the partner’s collected sperm. The resulting sac is the cocoon. Several cocoons may be formed from one mating session.

The cocoons are about the size of a grain of rice. White to begin with, they darken as they mature, into a reddish color when they are ready to hatch.

Which can be about three weeks, under ideal conditions. But if conditions are less than ideal, they can wait. Eggs can remain viable for up to a year.

Cocoons are more likely to hatch in warmer weather, after surviving the winter.

Cocoons have about ten eggs in each to start, but only
two to    six worm babies will eventually emerge. The tiny hatchlings are less than an inch long.

And absolutely adorable!

With good conditions and a good food supply, they can be full grown and ready to mate in two or three months.

Do Worms Really Have 2 Brains?

Sort of. While they don’t have an obvious brain, like snakes, rats or monkeys, most worms can be said to have two brains. They have two cerebral ganglia, which are connected all throughout their bodies—organs, skin & muscles. You could say their two brains are their body. Or, their body is their double brain. Or…they are all brain.

Motor and sensory signals run through nerve bundles throughout the body and chemo-receptors on their skin. These, obviously, enable responses to the environment. As well as maintaining bodily functions like circulation, digestion, respiration, heart rate, temperature
regulation, pain response, etc. Same as for everybody.

Doesn’t sound terribly impressive, does it? Yet, they have intelligence. Darwin suspected as much. He did an experiment with paper triangles expecting the worms to pull them from the points into their burrows, which would be the easiest, and that’s just what they did.

More recently, scientists put a worm brain into a lego robot. And it worked. Actually, they simulated the connections between C. elegans’ 302 neurons into software that was uploaded into a toy robot. And without any other extra programming, the lego robot behaved in ways
similar to the worm.  Not sure why that should be surprising.  Perhaps the fact that it is demonstrates the biases of the scientists, more than anything.

302 neurons is not a lot.  But considering how small and rudimentary they are, it seems hard to imagine that many neurons even fitting.  Life is amazing like that.  Still.  Worms are certainly not rocket scientists. But, so what? Unlike rocket scientists, they’re actually necessary to the formation and continued existence of Life on this planet.

Do Worms Really Have 5 Hearts?

While it depends on one’s definition of the word “heart,” the short answer to this question is…

Maybe!

They have 5 pairs of aortic arches near their head. An aortic arch is much simpler than a vertebrate’s heart, as it only has one chamber. But, since each pair could be considered a heart, or each individual arch considered a heart, that’s either 5 or 10 hearts. Or none. Because they’re not actual hearts, merely aortic arches.

They don’t have lungs, either, but still manage to oxygenate their blood.  They do this in two different ways. The first way is through the process of peristalsis.  They breathe by taking air in through their throat and pushing it back out through muscle contractions. And the other way is through diffusion, where a gaseous exchange happens through their moist skin. Moisture is
required for this. The freshly oxygenated blood is circulated through the body by the dorsal and ventral blood vessels.

So There You Have It                                     

Worms are surprisingly complex little creatures, amazing in so many ways. Researching this article was both exciting and, kind of overwhelming. I couldn’t stop! There is still so much more, so much more detail.
But I wanted to simply write a nice overview. Comprehensive but not torturous. I hope you learned something and enjoyed doing so. I know I did!

And, as always, I would be happy to hear from you in the comments.

Oh!  And be sure to check out my unprecedented worm poetry —  

The Secret Life of Soil Organisms – Part 1

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