Why do worms reproduce asexually

Questions about earthworms

Question from:
Date: 12.2.2008

I'm currently studying earthworms with my third, fourth and fifth graders and we still have some unanswered questions on the subject.
In the course of our observations we have established that the earthworm "divided" itself; is that a defense mechanism? Are babies born in the process?
How do earthworms multiply? We know they are hermaphrodites, but do they lay eggs or give birth to young earthworms?
How can you tell their age?
Thanks.

Caroline Carsberg


Answer from:
Date: 13.2.2008

Good day,

The earthworm does not "divide" by itself. This only happens accidentally, unlike other types of worms (water worms), which reproduce asexually by dividing. A new worm then emerges from each segment. But even if the earthworm is accidentally split (through an "accident"), a new worm can arise from each of the two parts. The front part is able to regenerate all organs of the worm, while the rear part is only able to do so if it is long enough.

Earthworms reproduce sexually. Although they are hermaphrodites (double sex), mating occurs and self-fertilization is not possible. During mating, the worms cling to each other in such a way that each of them can release its sperm, which emerge from the male sexual opening in the 15th segment, to the other. The sperm get into the female genital orifices, which are located at the 9th / 10th Segments are located where the clitellum (a saddle-shaped thickening, also called a belt) is. The sperm are then stored in a special organ: the seminal receptacle (Receptaculum seminis). The egg cells only mature later and are gradually fertilized by the sperm from the semen pouch. The fertilized eggs are deposited in a kind of cocoon, which consists of a very viscous mucus secreted by the clitellum. The worm takes several weeks to develop in this cocoon, the exact time depending on the species and temperature. A worm develops immediately, there is no metamorphosis, and no "free" larvae either. When hatching, a tiny worm is born which consists of a small number of rings and whose way of life is similar to that of the adult animals.

The number of rings in the earthworm is proportional to its age: over time, new rings are formed, i.e. the older the worm is, the more rings it has. However, I don't know how to tell exactly how old you are.

Best wishes
D. Pol

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