Monarch Butterfly: Life Cycle and Migration

Also known as the Milkweed Butterfly, the monarch butterfly is so called because its larvae eats the milkweed plant. Actually, the milkweed is the only thing the larvae can eat! Here is more information on the monarch butterfly, its life cycle and migration.

Life Cycle of the Monarch Butterfly

The life cycle of the monarch butterfly can be categorized into four developmental stages. The first stage is the egg, the second the caterpillar (larva), the third the pupa (chrysalis) and the last the adult, which heralds the emergence of the most beautiful creature on Earth, the monarch butterfly of course!

The female butterfly begins the next cycle by laying one small; pinhead sized white egg underneath the leaf of a milkweed plant. The caterpillar begins to develop inside, drawing upon the yolk material inside the egg for nutrition. It takes the caterpillar about 3 to 5 days to eat a hole in the egg case and emerge onto the surface of the leaf.

Now the caterpillar is about 0.1 inches long and weighs about 0.55 milligrams. Its body is covered by nine chocolate-covered rings, apart from a black head, three pairs of front true legs with claws and five pairs of prolegs extending backwards. This feature adds a unique and functional form to its body. The caterpillar also has a stomach, mouth and a silk gland among other characteristics of a full-grown caterpillar. It is the caterpillar’s rapid growth that leads to four or five molts (shedding of its external skin).

At this stage, the butterfly’s weight has increased to 1.5 grams. It is now about 2 inches long with yellow, white and black stripes on its body. Now it stops eating and spins a white silk pad on a stiff object, attaching itself by its two rear prolegs to the silk pad. Once this is done, it hangs head down in a J- shape in a seemingly inactive stage for about 12 hours.

Once this stage ends, the caterpillar begins to convulse in rhythmic jerks, breaking off its outer skin. At this developmental stage, its head capsule and its 16 legs are shed in about 60 seconds, with the emergence of a pupa or chrysalis that is 1 inch long and 0.4 inches in diameter. Jade green in color, the chrysalis at this point has 24 metallic appearing gold spots surrounding half its upper abdomen. The remaining part of the chrysalis is surrounded by 12 metallic-like gold spots. All these are crucial for the normal development of the butterfly.

As the caterpillar’s head capsule was discarded in the last stage, the caterpillar now enters the chrysalis stage without any vision and with only the ability to distinguish light from darkness. Now the inside portion of the chrysalis that is located below the gold crown turns to a jade green liquid within the first 16 hours, because of the disintegration of the various parts of the caterpillar’s body. The outline of the butterfly’s wings can now be viewed through the somewhat transparent outer shell, not only that, one can also see a pattern of lines that mark the position of the future butterfly proboscis (tubular sucking organ, used to suck sweet nectar from the flowers), first and second pairs of legs and also the two antennas.

The caterpillar emerges from the chrysalis after 8 to 14 days. It pumps fluid from its abdomen into the wing veins and is ready to fly in about 15 minutes. It takes approximately 2 hours for the wings to dry and the butterfly is full grown. Now, this creature has six legs and four beautiful wings that are surrounded by a narrow black border studded with white spots. At this stage, the adult has two compound eyes and is about 1.3 inches long and 0.15 inches wide and weighs about 0.41 grams.

Migration of the Monarch Butterfly

It is in autumn that the Eastern populations of monarch butterflies migrate south for two months to the Neovolcanic Mountains of Mexico. It is here that they cluster in tree from 9000 to 11,000 feet elevation for about 4 months in the months of November to March. This period also allows them to hibernate. It is during this interval that they eat and drink little, which in turn enables them to live as long as one year. It is during the spring that the monarch butterflies migrate from Mexico northeast towards the U.S. At this time, some of the monarch butterflies return the long distances to where they were born while others fly only part of the distance to Texas or the lower southern states. The monarch butterflies located at the west of the Rocky Mountains travel to the west coast from Baja Califronia to the north of San Francisco. There are others that come from British Colombia in the autumn to winter in California. These monarch butterflies have life spans of about six weeks.

Threats to the Monarch Butterfly

It is unfortunate that the population of the monarch butterfly has been greatly reduced because of the recent illegal deforestation of its over wintering grounds. Steps to classify it as a protected species and restore its habitat are underway. Another threat to monarch butterflies is that these beautiful creatures are susceptible to Ophryocystis elektroscirrha. This is a parasite that parasitizes them. This parasite results in decreased weight, shortened life span, rapid weight loss and weakened wings. These effects vary between butterfly populations and parasite strains.