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Monarch butterfly life cycle

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Click on the stages to learn more about the life cycle of the monarch butterfly.




Females lay tiny creamy-yellow eggs generally on the underside of a milkweed leaf.


Eclosion (hatching) occurs in 4–8 days, depending on the temperature.


As the larva develops, the egg changes in colour. The egg is grey when it’s about to hatch and the black head is visible. If you use a magnifying glass, you can see it moving around.


Head or tail

Soft, black filaments are at either end. The filaments behind the head wiggle when the larva feeds. Note that the filaments are not antennae. Three pairs of true legs are near the head. Each leg has a single claw. Prolegs are at the back. These help the larva cling to the plant.


As the larva grows, it has to moult (shed) its exoskeleton (skin). A monarch larva moults 5 times. The stage between moults is called an instar.

An eating machine

The larva emerges to become an eating machine. In 2–3 weeks, it grows to about 2,700 times its birth weight. If a human baby grew in a similar manner, it would weigh 8 tonnes when 2 weeks old!


Silk mat

The larva’s 5th and final moult comes when it weighs about 1.5g and is about 55mm long. The larva finds a sheltered site and produces a tightly woven silk mat. It hooks its rear prolegs into the silk and hangs downwards.

Final moult

Hormones kick in, and within 2 days, the larva moults into a pupa.



Chrysalis is a Greek word for gold. Scientists are unsure about why the gold band and spots appear on the chrysalis.

Bodily changes

While in the pupal stage, the larval tissue reassembles itself. The straw-like proboscis replaces jaws. Wings and reproductive organs develop.


After about 10 days, the final moult reveals an adult butterfly. The enlarged abdomen is full of fluid. The butterfly pumps the fluid into its crumpled wings until they become full and stiff.



Adult butterflies do not continue to grow but remain the same size for life.


The antennae detect pheromones – odour chemicals – used in courtship.


Butterflies use their feet to locate and taste nectar.


Male butterflies have two spots on the hindwings. Females have thicker black webbing within the wings. Females lay between 300–400 eggs at a rate of up to 40 per day.