Monarch butterflies are the most known of all butterflies in North America. One of the most interesting facts about these beautiful butterflies is their annual migration. One individual butterfly does not make the entire roundtrip; it usually spans four generations to complete the trip as the butterflies fly between 2000-3000 miles to reach their winter homes. The monarch is the only butterfly that migrates in both directions.
How to Spot a Monarch Butterfly
The monarch butterfly is distinct with orange wings that have black veins and margins and two rows of white spots within the margins. The underside of the wings is more yellow-brown and the spots are larger. The forewings have a few spots of orange near the tip of the wings. The wings span of the monarch butterfly is 8.9-10.2 cm (3 1/2 -4 inches). The butterfly has six legs but only uses four of them; two front legs are tucked up neatly against its body.
The male monarch butterfly is slightly larger than the female and the black veins and margins are a bit narrower. The male also has a black patch of minute scales in the center of its hind wings which dispenses pheromones to attract females for mating.
The Monarch Butterfly Migration
Monarch butterflies are most commonly found in Southern Canada to Northern South America, but have been found in other areas of the world. On the North American Continent, the migration of the monarch butterfly starts in August going until the first frost. By the end of October, butterflies from east of the Rocky Mountains migrate to Mexico. The western population of butterflies spends the winter in central coastal and Southern California in the United States, most notably in Santa Cruz and Pacific Grove. The butterflies stay in the same trees every year. This is one of the mysteries of the monarch as it is not the same generation of butterfly that makes the journey in subsequent years.
How do future generations of monarchs end up in the same locations as their ancestors? The first three generations of the monarch only live up to six weeks; it is the fourth generation that makes the migration to a warmer climate, hibernates, and starts a new generation in the spring time. The flight patterns of the migration seem to be inherited. Researchers discovered the butterfly uses a combination of sun position in the sky and a time-compensated sun compass which depends upon a circadian clock based in their antennae. There is also some indication the butterflies use the earth's magnetic field for orientation.
Sources of nectar are essential for migrating monarchs to survive. Adult monarchs feed from a variety of flowers that hold nectar. In preparation for the trip south to California and Mexico, the monarchs consume enough nectar to build up fat reserves. As they make their way south to their winter habitats, the butterflies gain weight. Similar to the bear, the monarch butterfly hibernates in the winter, feeding very little if at all during the winter months.
In the spring the monarchs leave their overwintering sites and head north. The Mexico wintering monarchs usually travel to Texas, feeding on nectar along the way. In Texas, they breed and then die. The new monarchs that emerge continue the journey north. Three generations later, the monarchs have completed the journey north and are preparing to start the migration south. The monarchs overwintering in California make their way to southern Canada, again, taking three-four generations to reach their destination before beginning the new migration cycle as well. The last generation of the monarch is non-reproductive; this is the generation that migrates to the south for the overwinter sites.
The Reproduction and Growth of the Monarch Butterfly
Reproduction of the monarch generally starts in February and March. There are two phases of the mating ritual for the monarch butterfly. The first phase is the aerial stage when the male attracts the female and nudges her, eventually taking her down to the ground. The ground phase is the coupling stage when the butterflies stay attached for 30-60 minutes.
During the 2-5 weeks of life, the female has at least one hundred eggs to lay as she continues her flight north. The eggs are miniscule, about the size of a period, and are laid one by one on its own milkweed leaf. The egg is the first stage of the life cycle of the monarch butterfly.
The second stage happens in about four days when the egg hatches. From the egg emerges the larva, or caterpillar, which immediately consumes the egg casing and begins to feed on the milkweed. Milkweed is the only food source for the caterpillar of the monarch butterfly. It is the milkweed that makes the monarch butterfly poisonous to some birds and other predators and distasteful to others.
During this stage the caterpillar grows rapidly, shedding its skin five times before the pupa stage which takes about two weeks. The caterpillar's body is banded with yellow, black and white stripes; its head is yellow and black striped. It has a pair of black filaments on each end of its body and reaches a length of about 5cm (2 inches).
The pupa, also called the chrysalis, stage is the third stage of the life cycle. The caterpillar begins to spin a silk pad on a milkweed leaf or twig and hangs by its last pair of forelegs in an upside down "J" position. The cocoon is a jade color with gold markings. In about two weeks, the cocoon becomes transparent, right before the butterfly emerges. The wings are folded and fluid stored in the monarch's abdomen must be pumped into the weeks as it emerges.
The final stage of the life cycle is the adult stage. This is when the butterfly has emerged from the cocoon. Usually the monarch emerges in the morning hours and will hang for several hours to let the fluid pump into the wings and the wings to dry. By the afternoon, the butterfly is ready to fly and feed on the nectar of the flowers. The monarch butterfly lives 2-5 weeks before reproducing and laying eggs for the next generation. However, some of these butterflies can live up to nine months.
The beautiful monarch butterflies are frequently studied to unravel the mystery of their migratory patterns. Activists fear for the natural habitats of the monarch as milkweed is considered weeds in some areas because some species of the plant are noxious or even poisonous to cattle and other animals. However, the monarch larva only feeds on milkweed. Nutrients and chemicals in the milkweed are essential for the metamorphosis to take place; if milkweed is eliminated entirely, the monarch caterpillar would not be able to develop into a butterfly. The balance of the environment requires the symbiotic relationship of the majestic monarch butterfly and the poisonous milkweed.
The copyright of the article "Following the Monarch Butterfly Migration" is owned by Cheryl Weldon and permission to republish in print or online must be granted by the author in writing.