A female monarch will only lay her eggs on plants in the milkweed family, as it is the only group of plants that the young caterpillars will feed on. The butterfly adult will lay her eggs on the undersides of leaves, the young caterpillars will eat the foliage, and the newly emerging adult butterflies will take nectar from the flowers. The eggs usually hatch in just about 10 days, although some are laid in the fall and do not hatch until warm spring weather arrives. The caterpillars emerge and immediately begin to eat and grow. They reach maturity after several weeks to several months, depending on the species, the abundance of food, and the temperature.
Development is fastest in warm temperatures.
At maturity, the caterpillars look for a place to pupate. The moth pupa is either enclosed in a silken cocoon or formed in some protected place as within the plant itself, in debris on the soil surface, or buried in soil. The butterfly pupa, also called a chrysalis, is attached to a stem or some other support and usually is much more exposed than a moth pupa. At this stage a dramatic transformation takes place. Many of the internal organs, muscles and nerves dissolve and the resulting fluids form new structures, producing a creature whose appearance and function are entirely different.