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C. elegans is a monoecious species with self-fertilizing hermaphrodites and some males. In the hermaphrodites, eggs and sperm develop at different times within the same gonad. Eggs are contained in the uterus and amoeboid sperm are contained in the spermatheca. The uterus has an external opening ; the vulva. The female genital pore is near the middle of the body, while the male genital pore is near the. tip. In anatomical males, specialized structures called copulatory spicules on the male's tail hold in place and open the female's vulva, into which amoeboid sperm travel to the spermatheca.

Fertilization is internal and embryonic development stars very soon after fertilization. The embryo is released from the vulva during the gastrulation phase. The embryonic development lasts 14 hours; It then proceeds through four successive larval stages with molting and ecdysis between stages—L1, L2, L3, and L4—leading to the development of a young adult worm. Adverse environmental conditions, such as overcrowding or lack of food, can lead to the formation of a transitional larval stage known as a dauer larva.