Monarch butterflies are one of nature’s miracles.
Bright and colorful, graceful beauty, but with the power and stamina to brave the windy Great Plains and travel thousands of miles.
Most of North America’s Monarchs (Danaus plexippus) spend the winter clustered together in forests high in the mountains of west-central Mexico. There in the Reserva de la Biosfera Mariposa Monarca, Monarchs cling to the trunks and branches of towering oaks and evergreen trees. West of the Rocky Mountains, a much smaller population of monarchs migrate to forests in California for the winter.
They cluster together to stay warm in the cool mountain night air, sometimes so thick that their weight can bend or snap the branch.
In February and March the females lay eggs that hatch into colorful caterpillars in a few days. The caterpillars eat milkweed leaves and grow for about two weeks, then attach themselves to a twig, shed their outer skin and change into a chrysalis in a few hours. Two weeks later, a full-grown butterfly emerges from the chrysalis!
This new generation of butterflies head north. Arriving in places like Texas and Louisiana several weeks later, they lay eggs on milkweed plants and start the cycle again. The new generation continues the journey north. It often takes four or five generations to reach their destination.
Monarchs spend the summer throughout the United States and into Southern Canada. For some monarchs, that makes the trip to Mexico 2,500 miles or more. While monarchs scatter widely, the core habitat for the largest share of monarchs is in the upper Midwest and Great Plains, formerly covered by tallgrass prairies. That tallgrass prairie had a variety of milkweeds and flowering plants with nectar, and provided ideal habitat for monarchs and other butterflies and pollinators.
Milkweeds are critical for monarchs. They lay their eggs almost exclusively on milkweeds, and when they hatch the caterpillars fatten up on milkweed leaves. Milkweeds contain glycoside toxins that don’t hurt the caterpillars, but build up alkaloid in their bodies that is poisonous and bad tasting to predators. That natural defense continues after their metamorphosis into butterflies. As butterflies, monarchs feed on nectar-rich plants, so flowers are also important to monarchs.
Unfortunately, some 98% of America’s historic tallgrass prairie has been converted to cropland or urban development. Genetically modified crops that have been widely adopted by farmers allow the use of powerful herbicides that have effectively eliminated milkweeds and flowering weeds from corn and soybean fields. The widespread loss of milkweeds and forbs on the landscape is one of the causes of the large decline in Monarch butterfly populations over the last 20 years.
In the late summer, a final generation of monarchs is born. This generation heads south, flying an average of 25 miles a day as they journey back to Mexico. Unlike the earlier generations which live a matter of weeks, the generation that migrates south lives about 8 months. They make the journey to Mexico, then go into a very inactive state, conserving energy through the winter.
Like other pollinators, monarch butterflies help spread pollen from plant to plant. Many plant species rely on pollinators to fruit and reproduce — including plants that provide about one-third of the U.S. food supply. Like monarchs, pollinators like bees and moths are experiencing population declines. Farmers today often must transport hives around from field to field to ensure that fruits, nuts and vegetables are adequately pollinated.
Scientists are researching the causes for the decline in bee and other pollinator numbers, and it could be a combination of factors. For monarchs, the loss of milkweeds and nectar-rich flowers appears to be a very important factor.
The solutions to help monarchs must include restoring milkweed and flowering plants to the landscape in Nebraska and elsewhere. For more information on monarch butterflies and efforts to benefit the species, visit:
National Wildlife Federation’s monarch page
Milkweed Watch at the University of Nebraska
Save Our Monarchs Foundation
Our Grade 4-5-6 Wildlife Week Poster Contest Rules 2016
Photos by US Fish & Wildlife Service