City logo home page link

The Monarch Life Cycle

The Monarch Life Cycle

During her lifespan, a female monarch may lay hundreds of eggs. She deposits these pinhead-sized eggs on the underside of milkweed leaves, where they will hatch in 4-5 days, depending on the temperature. The newly hatched larva feeds voraciously on the milkweed, accumulating bitter chemicals from the host plant that help protect the monarch from predation by birds. Over the next few weeks, the caterpillar grows from 1/16th of an inch to about 2 inches in length, increasing its weight by a factor of 2,700. To accommodate this rapid growth, the caterpillar must shed its distinctively striped skin several times before it is ready for the next stage of its development.

The mature caterpillar usually leaves the milkweed to seek out a bare branch or similar sturdy surface. It attaches itself by spinning a silk anchor from which it hangs upside down in the shape of the letter "j". After settling down, the caterpillar sheds its skin a final time, revealing a beautiful green chrysalis decorated with delicate gold spots. Inside the chrysalis, the caterpillar's body is undergoing metamorphosis, the process by which its tissues and organs rearrange into the startlingly different body of a monarch butterfly. After two weeks, the chrysalis becomes transparent, signaling that the black and orange butterfly within is ready to emerge.

The chrysalis splits open along several joints, and the monarch butterfly carefully emerges. Its wings are still folded and crumpled from confinement in the chrysalis, so the butterfly must pump fluid from its body into the wings, expanding them quickly to full size. The butterfly then rests quietly for a few hours to allow the wings to dry and harden before embarking on its maiden flight. A female monarch has approximately six weeks to seek out nectar, mate, and lay eggs before she dies.