Like all butterflies, monarchs go through complete metamorphosis, passing through four stages: egg,
caterpillar, chrysalis, and adult. In warm summer weather, a monarch can grow from egg to butterfly in about
25 days, while cooler spring temperatures can stretch the process to six or seven weeks.
Each stage is fragile. Eggs, caterpillars, and even milkweed plants face threats from weather, predators,
parasites, and disease. Because of this, fewer than 10% of monarch eggs survive to adulthood in the wild — one
reason healthy habitat is so important.
Adult males and females look similar, but there are a few easy ways to tell them apart. Males have two small
black scent spots on their hindwings and slightly thinner wing veins. Females lack these spots and have
thicker, darker veins, giving their wings a more detailed look. Both sexes play essential roles in the
monarch's migration and life cycle.
The Eggs
Female monarchs lay their eggs one at a time, usually on the underside of young milkweed leaves in spring and
summer. Each egg is tiny — about the size of a pinhead — and attached to the plant with a small dab of glue. A
single female typically lays a few hundred eggs over several weeks.
Monarch eggs hatch in three to eight days, depending on temperature. Once the caterpillar emerges, it
immediately begins eating milkweed, gaining the toxins that help protect it from predators later in life.
Along the southern migration route, monarchs lay eggs as they move northward, ensuring the next generation
continues the journey.
The Larva (Caterpillar)
After hatching, the monarch caterpillar goes through five growth stages, called instars. Each stage lasts only
a few days, depending on temperature and how much milkweed is available.
The tiny first-instar caterpillar is pale and almost translucent. It eats its eggshell, then begins feeding on
milkweed, which provides the toxins that later protect the butterfly. With each molt, the caterpillar becomes
larger and more boldly striped in black, yellow, and white, eventually developing the familiar pairs of black
tentacles.
By the fifth instar, the caterpillar has grown dramatically — more than 2,000 times its original size. At this
stage it eats constantly, storing energy for metamorphosis. When fully grown, it leaves the milkweed plant and
may travel several meters to find a safe place to form its chrysalis.
The Pupa (Chrysalis)
When the caterpillar is fully grown, it leaves the milkweed plant and finds a safe, sheltered spot to
transform. It attaches itself with a silk pad and hangs in a J-shape for several hours. Then its skin splits,
revealing a smooth green chrysalis underneath.
Over the next day, the chrysalis hardens into its familiar jade color with delicate gold markings. Inside, the
caterpillar completely reorganizes into an adult butterfly. After about 8-15 days, the chrysalis becomes
transparent, and the orange and black wings of the monarch can be seen just before it emerges.
The Adult
After about two weeks inside the chrysalis, the adult monarch emerges. It hangs upside down while its wings
expand and harden, a process that takes several hours. Once ready, the butterfly begins to fly and feed on
nectar from a wide variety of flowers.
Breeding-season adults reach maturity in just a few days, but the special generation that migrates does not
become reproductive until after overwintering. Most adults live 2-5 weeks, while migratory monarchs can
survive much longer.
Adult monarchs are known for their bright orange wings with black veins and white spots. Their wingspan is
typically 3.5-4 inches, and their colors and wing shape can vary slightly depending on whether they are
migratory or non-migratory.
Monarchs use only four of their six legs for walking, as the front pair is reduced — a trait shared by all
brush-footed butterflies.