The Monarch Butterfly is an icon of summer across much of North America. The brilliant orange and black butterfly flutters on the wings of summer from coast to coast and from Canada into Mexico. With its large wingspan of four to five inches and its bright colors it is perhaps the mostly widely recognized butterfly in its region.
The Monarch is of course an insect and like most insects it undergoes a metamorphosis through a variety of different body forms. Some insects pass through over a dozen different forms during metamorphosis, but the Monarch has only four stages. Yet each stage is so different from the previous that the metamorphosis of the Monarch is a wonderful transformation to observe.
The Monarch starts life from very humble beginnings as a tiny, almost imperceptible egg. These eggs are laid on the bottom sides of leaves, usually the leaves of the milkweed plant. The egg is much smaller than the head of a pin. The eggs have tiny ridges running down the length of the egg and are almost translucent in color.
Eventually the caterpillar emerges from the egg. Frequently the first thing that the Monarch does during this larval stage is to eat its egg casing. This is symbolic of the entire caterpillar life, it is an eating machine. Almost all of the caterpillar's activities are centered around eating. Interesting enough there is only a single type of plant that the Monarch caterpillar eats, the milkweed.
The Monarch has a very important relationship with milkweek. The milkweed is the host plant for the Monarch. The Monarch is able to extract a chemical from the milkweed called cardenolides. This chemical is poisonous to vertebrates (animals with back bones) and helps protect the Monarch from predators. In fact the bright colors of the Monarch actually work as a sign to predators that warns them to stay away from the nasty tasting Monarchs.
The Monarch eats so much that it out grows its skin and has to molt to get new skin. The old skin splits and the caterpillar walks out of it with a baggy new set of skin. During the larval stage the Monarch will molt five times. Each time it molts the black, yellow and white skin is a little brighter than the previous one.
When it is done with all the eating it has grown to be over 20,000 times bigger than when it started. Finally it can eat no more. The caterpillar crawls to the underside of a branch or leaf and prepares for its next stage of metamorphosis . It weaves a tiny silk pad called a "button" onto its perch. Then it attaches its back end to the button and hangs upside down.
Soon the caterpillar's head end curls up a bit so that it is hanging in the shape of a hook or the letter "J". It hangs in this position for about twelve hours. Frequently it will wiggle around, or shake from side to side. Eventually during one of these wiggling episodes the skin splits at the bottom of the "J".
It is as if the caterpillar's skin unzips. All of the caterpillar's features, its antennae, its eyes, its legs, its stripes, all slide up to the button and then drop off like a tiny pile of crumpled clothes.
Underneath the discarded skin a strange, amazing change has taken place. A brillant emerald green chrysalis with a crown of metalic gold spots has replaced the black, yellow and white caterpillar. At this point the Monarch essentially dissolves, and in the next week will reform itself.
At the end of the weeks time the outer chrysalis becomes transparent and features of the adult can be seen within. Then the butterfly tears the outer casing of the chrysalis and slowly emerges. Its body is full of fluid and its wings are tiny and shriveled, much smaller that its abdomen. For a few hours the Monarch rests on the casing of the chrysalis as fluid slowly drains into the wings. The wings grow several times larger as they fill. Then the wings dry out and become firm.
Now the Monarch experiences a new awakening and a new way of life. Instead of being anchored to leaves it is now free to fly. Instead of eating only the milkweed, it can now sip the nectar of a variety of flowers. And while it flies across the fields anyone that is fortunate enough to see it knows that summer is truly here.