How Do Segmented Worms Reproduce?

Identification

• Segmented worms, as their name suggests, have segmented body parts. Insects, spiders and other arthropods are the only other animal group with this structure. Segments are useful in the development process, as it is more efficient for the animal to develop from identical base components. Segmented bodies are also useful in locomotion, allowing the animal greater flexibility. Worms have an obvious enlarged area, called a clitellum, in the first 1/3 of the body. This specialized structure functions in reproduction.

Habitat

• Terrestrial segmented worms live and breed in soil. Some species can live in rotting logs and other places where conditions are similar to soil. Worms require moist, dark surroundings for survival and reproduction. They breathe through their skin by transferring oxygen trapped in the moist soil. Too much moisture in the soil, as happens after a heavy rainfall, will inhibit respiration. Worms will climb to the surface of the soil and are often found there after rain.

Mating Behavior

• To mate, two worms come together in opposite directions. They line up their clitellum with the sperm-producing segments (segments 9 and 10) located on the other worm, and transfer sperm. A mucous layer (sheath) forms over the clitellum. The worm begins to shed the mucous layer after copulation. As the worm is crawling out, the sheath passes over the female reproductive organs where eggs are released into the sheath, and the male parts where the stored sperm is also released. Once the worm has completely shed the mucous layer, this sheath forms a cocoon of fertilized eggs that eventually hatch.

Significance

• Earthworms are responsible for processing dead plant material into nutrient-rich soil. Along with recycling nutrients, the tunneling behavior of earthworms also helps to mix plant debris into the soil for faster decomposition. The tunnels create spaces for plant roots and allow water to travel deep into the soil. Adequate soil conditions will allow an earthworm to produce up to 80 cocoons per year, each with approximately 20 eggs, perpetuating this nutrient cycling service.