She flies from plant to plant, placing her tiny eggs carefully, each one of them alone on the underside of a milkweed. Within a few days, a head is visible as a black speck within the egg. The nearly microscopic mandibles begin to munch their way out—the only meal that isn’t milkweed for their entire caterpillar existence.
For the next two weeks, the caterpillar eats and grows, eats and grows. Each time it becomes too big for its skin it molts and each of these segments of caterpillar growth is known by the magical name of instar. Instar; in-star; in the star phase of life. The caterpillar is both earth bound and celestial: small and quiet in its larval body, and in some way shining with its own burning starlight as it grows toward its wings.
The caterpillar will grow through five instars in fourteen days. If it were the size of a human baby when it hatched, it would now be the size of a standard school bus. As it reaches the capacity of its skin in the fifth instar, it consumes one entire leaf of milkweed and takes a last walk on its caterpillar legs. It may walk as far as ten meters from that milkweed plant before it climbs to a high place and stops. This could be under the eaves of your roof, the underside of a tree branch, or the handle of a wicker garden basket that sits high on top of a storage cabinet on the front porch.
Once it finds a suitable location, the caterpillar spins a little silk button in the place where it will hang for the next two weeks. Then it dangles by its hind-end, straight down from that bit of silk. Eventually the head will curl upward so that its body looks like the letter “J.” If you were watching it during the next several hours, you would notice that the skin begins to look dull, the antennae-like tentacles on its head become limp and crinkled, and it is very still. Stick around for a while and you might witness the next amazing transformation.
First, the skin on its back splits, like an old zipper with dull teeth. The shiny and smooth, milky-sea-green body of the pupa will be visible underneath. Then it begins to move, twisting and writhing and squinching its body to shed its last caterpillar skin. As you watch, the dramatic spiraling movements of the pupa intensify until the crinkled skin falls off.
At the precise moment that the crumple of dead skin falls away, a shiny black stem with barbs on the end of it appears where the hind-end used to be, and pokes into the silk button. The stem is called the “cremaster,” a name that could possibly grace a heavy metal thrash band. If you were to look at a magnified image of this structure, you might imagine a medieval barbed mace, a tool of torture. The pupa continues to writhe and twists the cremaster around to entangle the barbs into the silk. Gradually, all motion stops. It is now firmly and peacefully affixed for the next two weeks of metamorphosis.
It will be a few hours before the milky-green, bulbous pupa hardens to become a chrysalis. A series of shiny metallic golden dots will appear along a horizontal ridge in the widest part. It is thought that these golden spots are small ports for oxygen. It is now a pendant of gilded jade, fit for the gorgeous winged monarch that will, in the fullness of time, emerge out of it.
Within the chrysalis, the contents that were once a caterpillar turn to a goo in which most of the cells are indistinguishable from one another. These undifferentiated cells are now called imaginal buds, a term that might lead one to wonder about an “imaginer.” Within that creative soup, the imaginal cells gradually differentiate and reorder to form a new body, legs, and head with real antennae. The wings are the last structures to form.
In the final 24 hours of transformation the colors of the butterfly develop. They darken the chrysalis until you see rich black and orange color within, and the shape of folded wings become visible through the now transparent outer shell. In a moment’s time the shell splits and the nascent butterfly drops out, crumpled and moist and swinging slightly as it clings to the shell with its new legs. The wings look tiny and deformed next to a disproportionately large, bulbous body. Its swollen body is full of fluid that the butterfly pumps into the veins in its wings until they flatten and widen. It must hang upside down letting the fluid settle and harden to strengthen the wings before it takes its first flight.
What happens next is dependent on the season. If it is midsummer, the butterfly will fly off, find nectar, and search for a mate. It will live a couple of weeks, reproducing as much as possible, and following the milkweed as it goes. And then it will die. The spring and summer are populated with several generations of Monarch butterflies.
If the days have grown shorter and the nights cooler, if the milkweed is beginning to die back, the butterfly that emerges will be part of the last generation of the year. Immediately its reproductive functions become dormant. Every bit of its energy is needed for what lies ahead. It fuels up on nectar whenever it can and flies south, joining millions of its kind on a trek that can be as long as 3000 miles, all the way to a tiny spot in southwest Mexico, in the state of Michoacán. This is a journey that every last North American monarch that is east of the Rocky Mountains will undertake. It will take them to the place where they will pass the winter.
Streams of monarch butterflies begin to arrive as the people of Michoacán are assembling elaborate altars for their beloved dead to celebrate the festival of Dia de los Muertos. They silently wing overhead and the people stop and welcome them with joyful, prayerful and tearful greetings, arms open. They are thought to be the souls of departed children returning for the festival. The color of the fluttering of thousands of wings echoes the profusion of marigold petals that grace the cemeteries as families gather to feast and celebrate with their dead while the veil between them is temporarily lifted.
Why Michoacán? It lies in the midst of three mountains in the Sierra Madre (“Mother Mountains”) which are covered with oyamel fir trees. Scientists have determined that the temperature and humidity of the air around these oyamel firs is perfect for the butterflies to overwinter in. On average it stays just warm enough to sustain their life if they cluster tightly together. Hundreds of millions of them do so, until the trees seem to be thickly layered in orange and black leaves. These trees are called “sacred firs” because the shape of them from a distance evokes the image of giant praying hands, finger tips pointing to the heavens. Imagine countless butterflies, their collective presence now becoming the shape of supplication.
Consider the following:
- This generation of monarchs is 5 removed from their ancestors who made this trip a year ago.
- All other generations live for only a couple of weeks while those who migrate hold on for up to nine months which earns them the name, “Methuselah generation.
- The thin wings and tiny muscles that worked almost continuously to bring them through rain and wind and over deserts, were fueled only by nectar in a dying season.
- The jubilant faces of the people who welcome them, the hands that pray, the beloved souls that return to feast.
These millions of monarch butterflies will cling to one another, fasting until the rebirth of spring. On one sunny morning, they will let go of their companions and with their tattered, nearly transparent wings, will flutter to the ground and drink the dew. They will find a mate, lay eggs on the nearest milkweed plant and die. A few days later, tiny caterpillars will emerge beginning a life that holds the promise of flight.
Each successive generation after this first breeding in the highlands of southwest Mexico, will fly farther from the sacred firs, following the milkweed north as it grows and blooms. Each life cycle is a step toward the possibility of one of the longest journeys undertaken by any insect on Earth.
Most will not make this pilgrimage, but all are a part of it.
Note: All photos are by the author except where noted
. . .
Monarch Watch is a nonprofit education, conservation, and research program based at the University of Kansas that focuses on the monarch butterfly, its habitat, and its spectacular fall migration.