Monarch Butterfly: Migration, Life Cycle & Facts

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

The monarch butterfly has a fascinating life cycle and migration pattern that is repeated every single year. Read this lesson to learn how an egg eventually becomes a butterfly and how incredible this species is!

About the Monarchs

The monarch butterfly is sometimes called the 'king' of the butterfly world. This species has an intricate cycle that takes place each year, which is described in this lesson. The monarch butterfly goes through four generations each year, and each generation has four distinct life stages: egg, larva, pupa, and adult. Let's break it down to really understand how and where each stage happens.

A female adult monarch butterfly.
female monarch

Monarch Life Stages & Migration

We'll start this journey in the oyamel fir forests of northern and central Mexico. It's around February or March and the temperature is just starting to get warm. Adult monarch butterflies emerge from their winter torpor (a period of inactivity similar to hibernation) and start looking for a mate. They mate and begin flying north, and the first eggs are laid in March or April. Female monarch butterflies lay eggs on the underside of milkweed leaves, and they may lay up to 300 eggs. These eggs are very small - about the size of a pin head.

Eggs incubate for about four days until a larva hatches. Larvae are small caterpillars, and their job is to eat and grow for roughly the next two weeks. They grow rapidly during this time and go through a series of molts, where they shed their exoskeletons as they outgrow them. The period between each molt is called an instar and a caterpillar will go through five instars. The first instar, right after hatching, is when they will eat their egg casing and the leaf they were laid on. During the second instar, they grow and begin turning yellow, black, and white. Colors become more vibrant during the third instar, and the tentacles become longer. White dots appear on the prolegs (the legs they use for attaching to things and walking) during the fourth instar, and at this point the caterpillar is about one inch long. By the fifth instar the caterpillar has black stripes and begins looking for a place to undergo metamorphosis.

The monarch larva, or caterpillar.
monarch caterpillar

The caterpillar will find a sturdy spot and attach to it using silk. At this stage, the organism is called a pupa, or chrysalis, and this is the stage where transformation takes place. The outside of the pupa will be soft at first and then harden to protect the organism during its change. At this stage it's green in color to help camouflage it against predators. The chrysalis stage lasts between 10-14 days, during which metamorphosis is taking place. The mouth turns into a straw-like tongue (called a proboscis) that is used to eat nectar from flowers, and wings begin to grow.

During the pupa stage, metamorphosis is taking place.
monarch pupa

Once metamorphosis is complete, the adult butterfly emerges. Afterwards, it takes a few hours before the wings are sturdy enough to fly, but then the butterfly heads off to feed on nectar and mate. This generation will live for 2-6 more weeks, laying eggs before it dies. The cycle is repeated, with the second generation of the year hatching in May/June, the third hatching in July/August, and the fourth hatching in September/October. The second and third generations repeat the four-stage life cycle, continuing north as the milkweed blooms (reaching the northern USA and southern Canada), but the fourth generation is different.

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