Butterflies mate through sexual reproduction, and mating begins when the male butterfly detects a female butterfly releasing pheromones at close range. If the female accepts the male, the male attaches to the female's abdomen, injecting a sperm packet into her stomach that she stores until she decides to lay eggs.
During mating, the male and female butterflies may go on a courtship flight that can last for an hour or more. As the eggs pass down the female butterfly's egg-laying tube, the sperm fertilize them. In monarch butterflies, courtship is composed of an aerial stage and a ground phase. The male chases, nudges and eventually takes down the female butterfly during the aerial phase. The sperm packet transfer takes place during the ground phase where copulation occurs. It is thought that the sperm packet also provides the female with energy sources that help her accomplish reproduction and remigration.
Although male butterflies can mate more than once, female butterflies only mate once throughout their lives. An adult female typically lays approximately 100 eggs. Some butterflies lay eggs in groups, but others lay a single egg distributed among many plants. After the larva stage, a butterfly produces a chrysalis during the pupa stage which generally lasts seven to 10 days.