Earthworms use slime-filled embraces and complex biological engineering to reproduce in the soil

Nature · Published 29 September 2026 Swipe more like this →

In short: Earthworms engage in surprisingly intimate rituals to ensure the next generation. By sidling up in opposite directions and encasing themselves in protective slime tubes, they exchange sperm before constructing specialized cocoons. This intricate process is just one way these creatures sustain their populations beneath our feet every day.

The reproductive cycle of an earthworm begins with the development of a fleshy, visible patch known as a clitellum. When two worms are ready to mate, they align their bodies in opposite directions and secrete a tube of slime that surrounds both individuals. Using specialized flaps on their clitella, the worms embrace, allowing for the external exchange of sperm, which is then stored in internal sacs for later use.

Once mating is complete, the worm produces a protein-rich sheath from its clitellum. As the worm shimmies this ring down its body, it passes over tiny pores to collect both its own eggs and the sperm received from its partner. The ring eventually slips off the worm's body, sealing itself to form a cocoon. Inside this protective vessel, the eggs are fertilized and develop into baby earthworms.

While many earthworms rely on this sexual reproduction, some species exhibit a different strategy called parthenogenesis. In these cases, the worms are exclusively female and do not produce sperm. Instead, they generate eggs that divide into identical copies of themselves. According to Sam James of the University of Iowa, this cloning capability allows a single individual to establish an entirely new population without the need for a mate.

Beyond their reproductive habits, earthworms are essential engineers of the soil. They consume organic matter, such as degraded plants and manure, and excrete nutrient-rich castings that provide nitrogen for plant growth. By burrowing through the earth, they create vital channels for air and water, while simultaneously mixing soil layers. This constant movement and processing of organic material make them indispensable to the health of the ecosystems they inhabit.

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