Earthworms are hermaphrodites, meaning they each contain male and female gametes. During mating, both worms exchange sperm and have eggs fertilized. The belt-like swollen area on the earthworm’s body, commonly called the "saddle" or "belt", is called a clitelum. It secretes a slimy substance that forms capsules which protect the eggs (sperm cells and eggs merge inside the capsule and form embryos). Inside, 1-20 eggs mature, taking between 60 and 90 days to hatch, depending on environmental factors such as humidity and temperature. An earthworm takes up to a year to fully mature, and in the wild they can live from 4 to 8 years.