Earthworm Reproduction
Hermaphroditic by nature, worms need only find another worm to mate and produce young, making them by sheer number, one of the most successful members of the animal kingdom. But their success is twofold: because of their ability to enrich soil via their droppings, they are also considered important contributors to the world's ecosystems. Does this Spark an idea?
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The Earthworm
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More than 1,800 species of earthworms inhabit most regions of the world and range in size from less than an inch to more than 10 feet, with an average length of 5 to 6 inches. Earthworms have no skeleton or shell and only a simple nervous system instead of a brain. In bodies that are not much more than bundles of muscle, they have no lungs, five simple hearts, light sensitive cells in their skin instead of eyes, and only a nerve cord in place of a spine.
The Mating Ritual
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Earthworms are hermaphrodites, which means they have both male and female organs, but they still need another worm to reproduce. To do this, they meet nose to tail, lining up so they can pass sperm from their sperm ducts to the male genital openings in segment 15, and then into the other's sperm receptacles, located in segments 9 and 10.
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Conception
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After sperm has been exchanged, the worms separate. The smooth rubbery band on each worm, called the clitellum (usually segments 31 to 37), then secretes a mucus to form a kind of tube that covers the front part of the worm. The ovaries, located in segment 13, release eggs into the egg sacs in segment 14. As the worm backs out of the slimy tube, a few eggs are laid in the tube and sperm is released. Once free of the worm, the tube pinches off and its ends seal, encasing the eggs and sperm in a kind of cocoon that then shrinks to about the size of a grain of rice.
Worms continue to create cocoons until all the exchanged sperm is used up. If conditions are right, new worms will emerge in about three weeks, but cocoons can overwinter in cold climates or wait out dry spells.
Regeneration
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Regeneration refers to the ability to regrow lost segments. In regard to earthworms, usually only a lost head or tail is regenerated but a study done by G.E. Gates in 1972 showed it is theoretically possible to grow two worms from one.
The Importance of Earthworms
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When it comes to earthworms, it's safe to say the more, the merrier.
Earthworms improve soil two ways: first by tunneling through soil, "eating it" and then depositing their droppings, called castings, on top of the ground. Castings are enriched with nitrogen, phosphorus, calcium and magnesium, all important nutrients for gardens and lawns.
Second, their tunnels serve to aerate the soil by providing passage for air and water, which contribute to healthy plant root growth.
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References
- Photo Credit earthworm image by ril from Fotolia.com
