Monarchs, like other butterflies and moths, undergo complete metamorphosis, meaning that they have an egg, larva caterpillar , pupa chrysalis , and adult stage. The egg and caterpillar stages occur only on species of milkweed genus Asclepias , whereas adults survive by nectaring on a variety of flowering plants.
Female monarchs only lay eggs on milkweed plants since monarch caterpillars only eat milkweed. The milkweed plant provides both food and shelter for a caterpillar for approximately two weeks dependent on temperature while it eats almost constantly, pausing only to shed its skin. The period between each shedding of the skin, or molt, is called an instar. Monarchs have five larval instars and grow to almost 2, times their original mass. A late fifth instar monarch will generally crawl away from the milkweed plant it was feeding on to find a secure location where it forms a silk pad and hangs upside down in a J shape before shedding its skin one last time to expose the bright green chrysalis.
In 8 to 15 days, an adult emerges, pumps fluid to its wings to give them shape, and spends several hours drying before it is ready to venture off to find nectar or a mate. While butterflies and moths do not care for their young after hatching, they do lay their eggs on the appropriate host plant, which will be food for the newly hatched caterpillars.
Monarch females usually lay a single egg on a milkweed plant, often on the bottom of a leaf near the top of the plant. Eggs are only about the size of a pinhead or pencil tip and are off-white or yellow, characterized by longitudinal ridges that run from the tip to the base. The eggs hatch about four days after they are laid. As females lay their eggs, they secrete a small amount of glue to attach the eggs directly to the plant.
Female monarch butterflies lay eggs over two to five weeks of egg laying, with a record in captivity of 1,! Each egg is formed inside the female prior to fertilization, including the hard outer shell, called the chorion, which protects the developing larva inside.
