Monarch Butterfly

North American Monarchs are the only ones that migrate vast distances. They travel up to 3000 miles (4800 km) to their winter habitat. Up to four generations of these Monarchs occur annually. Some live only a few weeks, others several months.

Let’s begin their journey in their winter grounds of California and Mexico. Here, as adults, they spend the winter in warmth, in clusters of thousands. In spring, they begin their northern journey, stopping along the way to feed on nectar and lay eggs on milkweed plants. Those adults will die along the way or when they reach their northern homes. Eggs will hatch on the milkweed plants and larvae will begin to feed, growing larger over the summer and molting several times before they pupate. Sometimes more than one generation occurs on their northward journey. When they emerge into adult butterflies, they will continue the journey north to their summer grounds. Here, they will again lay eggs on milkweed plants and then die. Their eggs will hatch in the north, grow up as caterpillars, pupate and emerge as adults and head southward as winter approaches. One female Monarch can lay several hundred eggs per year, one at a time on the underside or stems of milkweed plants.

Both the caterpillar (easily identified by its bright stripes of green, black and white) and the adult butterfly (bright orange with black lines and white spots) are examples of Warning Coloration. They scream “I’m Poisonous” so that predators know to avoid them. The milkweed that sustains them also gives them toxic defenses. A similarly patterned, although smaller, butterfly, the Viceroy is also somewhat toxic to some of its enemies, but by mimicking the Monarch’s colors, it benefits from the warning coloration even though it’s not quite as poisonous.

Monarchs are poisonous because one of their only food sources is milkweed, which is also toxic. A reduction in the number of milkweed plants is due to pesticides, urbanization and misinformation about their “noxious” status that has led to mass removals. Their wintering grounds are also at risk due to urbanization and forest fires. Along with interference in their migration routes due to road and city construction, the Monarch is in danger of having its life cycle severely interrupted. Although they have not been assessed by the IUCN, their status is thought to be Conservation Dependent as a series of conservation steps are being and/or should be taken to ensure their survival, including widespread planting and protection of milkweed species, migration routes and overwintering habitat.