By Lynn Colburn and Stacy McQueen
Monarch butterflies are taking flight. Some landed in Jacksonville on the evening of Friday, September 20, as a stop along their migration to escape the cold winter climate. Monarch butterflies are the most recognized butterfly in North America. National Geographic notes that monarch butterflies are known for the incredible mass migration that brings millions of them to California and Mexico each winter. Monarch butterflies east of the Rocky Mountains migrate to Mexico and the monarchs west of the Rocky Mountains migrate to California. Stacy McQueen, teacher at Virginia Elementary School, notes that monarch butterflies are the only insect that migrates to warmer climates and their annual journey which spans a continent, three nations and multiple generations can take them 2,000-3,000 miles away each year. The butterflies will arrive in October. How they know their way, sometimes even to the same trees, is a mystery.
Each generation goes through a life cycle from egg to larvae (caterpillar) to pupa (chrysalis) to adult butterfly. In February and March, monarch butterflies come out of hibernation, start mating and begin their journey back. The butterflies are dependent upon milkweed. They will lay their eggs on milkweed and it is the only food the caterpillars will eat. After about two weeks, the caterpillars are fully grown, and nearly 3,000 times their size. Each finds a stem or leaf to attach itself with silk. A chrysalis is formed to start the process of metamorphosis. Within 10-12, days a monarch butterfly emerges and flies away feeding on flowers and enjoying the two to six weeks of life they have left. The female butterflies lay hundreds of eggs and continue the cycle. The generation born in September and October begin the migration in October when the weather gets cooler, the days get shorter and the milkweed dries up they know it is time to go.
Monarchs cannot withstand freezing winter weather. McQueen notes that these butterflies will not fly if the temperature is lower than 55 degrees Fahrenheit. Monarch butterflies only migrate during the day. Normally solitary during the summer months, they often cluster together in large numbers as they migrate south. A cluster of butterflies is called a roost. This roosting behavior is an anti-predator strategy. Cool temperatures paralyze monarchs, making them vulnerable to predators such as wasps, ants, parasitic flies, birds, snakes, toads, rats, lizards, dragonflies and spiders.
A roost provides safety in numbers. When overnight temperatures are warm, monarchs may not gather as tightly or roost at all.
The monarch wintering sites are under threat because of people cutting down their favorite trees to build roads, houses and farms. National Geographic notes that many scientists are concerned about the eastern population of monarchs, which summer east of the Rocky Mountains. This group is occurring in ever smaller numbers, and its survival may be threatened by a series of natural disasters in the Mexican wintering grounds, as well as by reduced acreage of milkweed plants in their summer home.