Royal Insect Beauties
Monarch butterflies (Danaus plexippus) are extremely popular butterflies of North America, and are also known by such other names as milkweed butterflies and common tiger butterflies. These butterflies are well known for their strikingly beautiful appearance. The vibrant orange, black and white coloration, along with the stripes and spots on their wings, makes the Monarchs easily distinguishable from other butterfly species with the exception of the viceroy butterfly with a similar appearance. The wingspan of the monarch ranges between 8.9 to 10.2 centimeters. The monarchs exhibit sexual dimorphism, where the males are larger than females and bear slight variations in the color patterns of their bodies. The butterflies possess six pairs of legs, of which the forelegs are vestigial in nature. Only 1% of the monarch butterflies are of the rare grayish-white variety known as the “white monarch”.
Life Cycle and Migration
The monarch butterfly eggs are laid on the underside of leaves of the milkweed plants. These eggs hatch in about four days to give rise to the larvae or caterpillar which voraciously feeds on the milkweed plant to store energy as fat to be utilized during the non-feeding pupal stage of the butterfly. During this time, the caterpillar also passes through 5 distinct stages, separated by a molting event. After each molting event, the caterpillar achieves a larger size than its previous stage. Finally, after two weeks, the caterpillar forms a silk cocoon around itself on a horizontal substrate, hanging upside down from the cocoon, where it undergoes the transformation into the beautiful adult monarch butterfly. In about ten days, the adult emerges from the pupa and lives for about 4 to 6 weeks within which time it mates. The adults that emerge as part of the late summer generation. however, survive much longer, for about 6 to 7 months within which time it migrates southwards from northern areas to survive the cold winters of northern North America.The migration of these monarch butterflies is regarded as one of the most spectacular natural phenomena of the world. The butterflies begin their migration in the months of September and October, starting from their habitats in Canada and the United States and fly towards the overwintering sites in Mexico. The butterflies start their return trip in March, and arrive at their summer habitats by about July. At least 5 generations of butterflies are involved in this entire migration episode.
Feeding and Social Behavior
The monarch caterpillar feeds extensively on the milkweed plants till it enters the pupal stage while the adult butterflies sip the nectar of flowers. The monarchs in both the caterpillar and butterfly stages thwart predators with their aposematic nature. The monarchs acquire the cardenolide, a type of cardiac poison, from the milkweed plants during the caterpillar stage of the monarch’s life cycle. These cardenolides remain in a concentrated form in the body of both the caterpillar and the adult butterfly and lends a distasteful taste to the bodies of these butterflies. This discourages predators from feeding on the monarchs.
The monarch butterflies are currently facing a major threat to their existence. The habitat of these butterflies is being constantly lost to deforestation, milkweed plant destruction, and climate change. With global temperatures soaring high and world climate becoming more unpredictable in nature, the migration patterns of the monarchs is disrupted badly. As per a World Wide Fund for Nature report, the year from 2013 to 2014 witnessed the lowest migration numbers of monarch butterflies recorded in the last 20 years. The monarchs who heavily depend on the mountain forests of Mexico as their winter home are losing their habitat to human intervention in the form of clearance of these forests for agriculture and tourism.
Several environmental and wildlife organizations like the World Wide Fund for Nature are currently actively engaged in attempts to save the monarch butterflies. The most important step towards this goal is to protect the habitat of these butterflies. Unsustainable logging of Mexico’s forests need to be checked, and measures need to be adopted to ensure responsible tourism in these forests. The common milkweed plant, being the primary species sustaining the monarch populations, must be conserved as well in order to allow these treasured butterflies to thrive.
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