Earthworms!

By Doug Collicutt

(Click thumbnail images for larger photos.)

The Gardener's Friend

As every gardener and farmer knows, earthworms are very beneficial. But, other than that, most people know very little about the lives and biology of these lowly invertebrates. So, here’s a little primer on earthworms.

Earthworms belong to the class of invertebrates known as the Oligochaeta. Their soft bodies are arranged in discreet segments. There are about 3000 different species in the world. In Manitoba there are about 10 kinds or earthworms, but most of these are exotic species, having been brought here by European settlers along with their crops and other plants.

Earthworms live in tunnels in the soil that they excavate themselves. They use their burrows to move around quickly, both in search of food and to avoid predators. Their tunneling helps to aerate the soil and allows water to penetrate the surface instead of running off.

Worm Biology

Bits of dead animal and plant matter are food for earthworms. On a steady diet of this detritus, earthworms produce copious amounts of castings, or poop. A single worm can produce its own weight in castings each day. These are deposited on the ground surface, making new soil and nutrients available for plants. Earthworms are living compost machines! You can actually buy worm castings as fertilizer! In a healthy lawn or garden, however, there ought to be enough worms hard at work already. Under any given square metre of lawn, there may be 30 or more worms below the surface.

Some kinds of earthworms are so plentiful that they form the basis of a $100 million a year industry. Night crawlers (Lumbricus terrestris), or dew worms as they are also known, are harvested as fishing bait. They will cost you about $5 for a dozen in bait stores. Southern Ontario is the center of this industry and every year nearly half a billion (yes, 1/2 billion) night crawlers are collected by hand from golf courses and farmers’ fields for sale across North America. As their name implies, night crawlers come out at night to crawl around on the surface. Workers with lights search for and pick up hundreds of worms a night.

Earthworms are hermaphrodites; each individual worm has both male and female sex organs. Most kinds, however, require the sperm of another worm to fertilize their own eggs. To mate, worms must line up against each other, facing opposite directions, then line up their male bits to the respective female bits of the other. After the mutual mating, each worm will produce a capsule containing 2 eggs that will hatch into tiny new worms. Each baby worm will take about a year to grow to adult size; then it could live for as many as 10 years.

Worms on the Sidewalk

Everyone knows that earthworms come out in the rain, squirming around on the ground and slithering across sidewalks. There’s a common misconception that they are forced to the surface to avoid drowning in the saturated soil. Actually, worms have no trouble breathing in wet soil. They absorb oxygen through their skin and can live for long periods even in open water, as long as it’s well oxygenated.

Then what is sending them to the surface when it rains? Well, it’s not necessity that drives them to the surface, it’s desire! Yes, they’re looking for love in all the wet places. At least, that’s one theory. No one’s really studied the phenomenon that closely. The love-in theory suggests that, for worms, getting together is simply a lot easier in the 2-dimensional realm of the ground surface than it would be in the restricting tunnels of the 3-dimensional world of the soil. Heavy rain that wets the ground surface ensures the worms won’t dry out in the pursuit of love. The other, more boring, theory about what worms are doing out in the rain involves dispersal. They may be using the opportunity of having damp ground to move to new feeding areas or leave overcrowded sites.

In Closing

Earthworms are interesting creatures in their own right and they are more than just beneficial. All of what we eat originates in the soil. We owe are existence to earthworms and many other lowly creatures, that keep our soils healthy.

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More worm articles in NatureNorth: Night Crawler! | Night Crawlers in the Class Room