Life Cycle

The Life Cycle of a Monarch Butterfly

Before a butterfly can flap its wings, it starts out as something completely different and transforms itself through four stages. First as an egg, then as a caterpillar, next as a pupa in its chrysalis, and finally, it emerges as a butterfly. This entire process takes about four weeks from start to finish; although the warmer it is, the shorter the cycle. Let’s take a look at each stage in the life cycle of a butterfly:

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A butterfly begins as an egg, laid on the underside of a milkweed leaf. Inside is a tiny caterpillar, but you’ll have to look closely to see it since the eggs are very small – only about the size of a pinhead! A female Monarch will lay one egg at a time, up to 500! They lay so many because only about one in 20 make it to adulthood.


Inside the egg grows a caterpillar, or larva, and there are five parts to this stage, which are known as Instars.

1st Instar

After the egg is laid, the caterpillar hatches four days later. It’s pretty hungry so it eats its own eggshell and then the leaf the egg was on. The first bite of milkweed is a dangerous one, because milkweed latex can act like glue. Some caterpillars die from that first meal because their mouths gum up. If it survives, the caterpillar then takes a break to shed (or molt) its skin.

2nd Instar

The striking combination of colours yellow, white and black, begin to appear and the caterpillar will eat another leaf or two.

3rd Instar

Changes are becoming more noticeable in this stage. The caterpillar is bigger and its colours are more vibrant. Its tentacles grow longer.

4th Instar

The caterpillar is now about an inch long and has obvious white dots on its prolegs – those stumpy little legs that run down both sides of the caterpillar. At this stage, caterpillars can eat a whole leaf in under an hour!

5th Instar

This is the stage right before the BIG change, but there’s still a lot going on. Fattened up, and with soft, black stripes, the caterpillar moves pretty fast as it searches for a place to spin a silk button that attaches to the leaf in order to hang upside-down, form a ‘J,’ and molt one last time.

While hanging upside down, the skin splits behind the caterpillar’s head and it wiggles out from the old skin. It’s a tricky thing to do. It has to hold onto the silk button while slipping the rest of its skin off. Once this happens, the caterpillar becomes a pupa.


The pupa, or chrysalis, is soft at first but in about an hour, the shell hardens to protect the growing butterfly within. It’s a beautiful shade of green to help disguise it from predators. The pupa has no eyes, antennae or legs but inside a complete metamorphosis is going on. The mouth changes from what the caterpillar needed to chew milkweed leaves into a straw-like tongue that the butterfly will need to sip nectar from flowers. And it grows wings! All in just about two weeks.


Finally, the shell bursts open and a butterfly emerges. It takes a couple of hours before it can fly because its wings are tiny, wet and wrinkly. The butterfly pumps body fluid, called hemolymph, into the wings to make them grow big and strong. After the wings have hardened, it’s time to eat! The butterfly flies off in search of its first meal, which it will slurp up through its straw-like tongue, or proboscis. After just dining on milkweed, butterflies enjoy a little more variety and take their nectar from several different flowers, making them one of nature’s migratory pollinators.

The “Super Generation”

It takes a full year for the completion of the annual monarch butterfly migration from Texas up the eastern U.S. to southern Canada, and then a long journey to central Mexico to overwinter for several months in the cool mountaintops followed by the final leg back to Texas. It is a somewhat puzzling concept to wrap your mind around, but it takes 2-3 generations of monarchs to make the journey north from Texas to southern Canada but only 1 generation to make the entire trip south to Mexico.

The northern generations of monarchs only live 4-6 weeks on average as they follow the milkweed bloom – a plant they lay their eggs on and the only plant that caterpillars will eat. The generation that makes the longest leg of the migration south to Mexico, where it rests for months, will make the final short leg to Texas to complete the cycle, is known by scientists as the migratory generation. In the film they are termed the “Super Generation,” as they live 8 times longer than their mother and grandmother, the northern generations, and travel 10 times farther. In order to make the long journey they must conserve energy. They do so by not mating or having to use energy laying their 300 to 800 eggs, they also catch “free rides” on thermal air currents sometimes flying a mile high, and they store fat at an amazing rate compared to the northern generations.

While all monarch butterflies carry the DNA to make this long journey, it is only this southern flying generation that is triggered by various external factors in the fall to become a “Super Butterfly.” Outside elements such as the angle of the sun, the drop in the temperatures and longer days that occur in the Fall, trigger the changes necessary to make this extra long journey. The females do not sexually develop and enter a phase called sexual diapause, and therefore cannot mate, and these temperature and length of sunlight, also activate this generation’s ability to convert and store fat for the long journey.

After their long journey south, they overwinter in Mexico for several months in oyamel evergreen trees set high in a few isolated peaks in the cool Sierra Madre mountain range.

The Milkweed Plant

Named for its milky juice, more than 100 varieties of milkweed exist, and most are poisonous to many animals – but not to Monarchs. Female Monarchs normally lay one egg per milkweed leaf. As they grow, caterpillars fill themselves with milkweed poison. It’s not harmful to them and remains in their bodies forever. It stays in their orange and black wings, as a reminder to predators that they taste bitter.

A perennial that generally blooms between May and August, milkweed plants prefer soil that is rocky, sandy, and clay. They are hardy and beautiful plants, and as butterfly breeding grounds, will enhance your home garden with their bright flowers along with the natural magnificence of the butterflies that will rest there. Some farmers consider milkweed a nuisance, but it is essential to the survival of the Monarchs.

Learn more about Milkweed >

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