Earthworms

Nature Notes by Dr. Frank Lang

Dog and I ventured forth one morning several weeks ago to discover an earthworm disaster; worms all over the street. It is a kind of gruesome sign of spring.

What happened? Our first relatively warm soaking rains of spring filled available pore space in the soil with oxygen-deficient water. Because of a week or so of relatively warm weather, the earthworms moved up out of their deep winter burrows to the surface to eat and breed. Earthworms normally obtain oxygen for cellular metabolism by direct absorption through their moist skin into surface capillaries and hemoglobin-rich blood. Under most circumstances there is enough oxygen in the soil atmosphere to supply the worms, but there is not enough in the rain water to do the job. So out pop earthworms by the thousands, out of the grass and onto the street, where most of them perish by being crushed or from dehydration as the street dries out. I have never noticed earthworm predators taking advantage of such a bounty. I always expect to see robins and starlings out gorging themselves, but am always disappointed. Perhaps they don’t care for petroleum flavored worms. Earthworms can accumulate certain pesticides in their tissues at concentrations many times that found in the soil. Small mammals and birds that eat these earthworms accumulate the pesticides in even higher concentrations, sometimes fatal concentrations, in a phenomenon known as biological magnification.

Our local raccoons are fond of earthworms. Often in summer, after watering the lawn, I have gone to bed only to be awakened in the middle of the night by the “chirring” sound of raccoons talking in the yard. The next morning my lawn is pockmarked with shallow holes where the raccoons have been going after night crawlers.

I have gone stealthily creeping about lawns late at night myself, flashlight in hand, lidded bucket at my side, searching for the mighty nightcrawler. My purpose was not to eat them, but to use them for fish bait. Our large earthworms extend some distance from their burrows at night to forage and to mate.

Sex among earthworms is a curious business. They are hermaphrodites, that is, both boy and girl. Their internal sex organs and their external openings are arranged in such away that self-fertilization is not a possibility. Partners meet head to head in opposite directions, external openings of one meeting that of another.. .you don’t want to hear the rest of this! Children have been known to hear this program unaccompanied by an adult. Earthworm love involves the formation of a mucus sheath and an organ known as the clitellum, for heaven’s sake.

Worms’ rear-ends often remain in their burrows and they can retract with lightening speed at the slightest vibration or beam of light. You must grab the earthworm quickly, then pull gently, least you pull poor worm in two. This may not be as bad as it sounds for many species can regenerate a head or end and carry on. It is not nearly as bad as being empaled on a fish hook, however. Occasionally, if caught in the act, so to speak, you get two for one. I must confess I always hesitate. Nightcrawling takes great skill and stealth, enough for me to make it almost as much fun as fishing, considering my fishing skills.

Earthworms are extremely important soil organisms. They enhance the soil environment with their burrows by increasing soil aeration and drainage. They speed up the release of nutrients tied up in plant debris by munching up and partially digesting leaves. The partially digested leaves are mixed with soil particles, ground up in the worm’s gizzard and excreted as castings. Plant materials in the castings are broken down by soil microorganisms to a form that can be absorbed and reused by plants. Earthworms also mix the soil by bringing up soil from below the surface, as much as 40 tons per acre by some estimates. Earthworms are valuable contributors to the health and welfare of many terrestrial ecosystems.

— Dr. Frank Lang

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