Monarch Metamorphosis

February 10, 2001

Metamorphosis is the series of developmental stages  insects go through to become adults. Butterflies and moths have four stages of life: egg, larva (the caterpillar stage), pupa (the chrysalis phase), and adult. It takes a monarch butterfly just 30 to 40 days to complete its life cycle, with warmer temperatures generally being responsible for faster development.

Monarch females lay their eggs on milkweed, the only plant  monarch caterpillars can eat. The eggs are laid singly and generally on the undersides of leaves. The eggs are very small (about the size of the periods at the end of the sentences on this page) and are whitish in color. Three to six days after the eggs are deposited, they will hatch.

Immediately after hatching, the caterpillar is so small it can barely be seen. It grows very fast though, feeding on nothing but milkweed leaves. In just 9 to 14 days it is about 2" long and is now full grown. A caterpillar has eight pair of legs. The first three pair of legs will later become the butterfly's legs.

A monarch caterpillar sheds its skin five times during the larval stage. Similar to the way a snake sheds its skin when its body has outgrown the skin, a caterpillar does the same. A new, larger skin is always waiting under the one that is shed. See the caterpillar's shed skin laying just behind its tail end?

When the caterpillar is full grown it usually leaves the milkweed plant. It crawls (sometimes 30 or 40 feet away from the milkweed) until it finds a safe place to pupate. The caterpillar makes a silk-like mat and then attaches its last pair of legs to the mat. The caterpillar allows itself to drop and then hangs there, upside down in a J-shape, for about one full day.

The caterpillar's skin is shed for the last time as it passes from the larval (caterpillar) stage to the pupa (chrysalis) stage of metamorphosis. Under the caterpillar's skin this time is a jade green casing which is called a chrysalis. Inside the chrysalis, which is only about an inch long, the caterpillar will miraculously transform into a beautiful butterfly.

Immediately after the skin is shed, the chrysalis is very soft. Within an hour though, it hardens to become a protective shell for the caterpillar inside. Looking at picture, you can still see the ribbed body of caterpillar in the newly formed chrysalis on the left. The chrysalis on the right has hardened to become a beautiful jade green shell. Dramatic changes occur inside the chrysalis. The mouth parts must go from being those required for chewing (what the caterpillar needed to eat milkweed leaves) to what a butterfly will need: a straw-like tongue used for sipping nectar from flowers. And a creepy, crawling insect will become a flying insect, one of the most beautiful insects on earth!

In just 9 to 14 days the transformation from caterpillar to butterfly is complete. Through the chrysalis, you can now see the orange and black wings of the monarch butterfly.
   With no visible signs to signal the emergence of the butterfly from its chrysalis, the chrysalis suddenly cracks open and out comes the monarch butterfly. Its wings are tiny, crumpled, and wet. The butterfly clings to its empty chrysalis shell as hemolymph, the blood-like substance of insects, is pumped through its body. As the hemolymph fills the monarch's body and wings, they enlarge. Right now, this monarch is extremely vulnerable to predators because it is not yet able to fly.

About one hour after emerging from its chrysalis, the monarch's wings are full-sized, dry, and ready for flying. Here a newly emerged monarch uses it straw-like tongue, called a proboscis, to sip nectar from hardy ageratum (Eupatorium coelestinum). Four to six days after emerging from its chrysalis, a monarch butterfly is old enough to mate.....and so begins the life cycle of of the next generation.