The monarch butterfly, one of the few butterflies that migrates, is easily recognized by dark orange wings with black veins and white edge spots. As the days grow shorter, the fall migration begins and millions of monarchs make their way south.
This 4-inch butterfly is found throughout the United States and into southern Canada. From September to the third week of October, monarchs in central and Eastern United States make their way south to overwinter in the Gulf states and remote mountain valleys of southcentral Mexico.
Peninsulas are good areas to observe migrating butterflies. Point Lookout, Eastern Neck National Wildlife Refuge and Black Walnut Point in Maryland and Cape Charles and Kiptopeke in Virginia frequently attract monarchs. Migrating monarchs often rest at these and other southern tips before crossing water. The butterflies rest on narrow-leaved trees like willows, maples and pines.
By November, they have usually reached their winter destinations, sometimes 2,000 miles away. They will spend the next five months overwintering in a dormant state, massed on the trees in the Gulf States and Mexico. One wintering site may attract millions of butterflies. The sheer weight of so many butterflies can even break tree branches.
In March, as temperatures begin to rise, monarchs become active again. They mate and the butterflies, mostly females, begin to return north. This migration is not as spectacular as the fall migration. It is a long drawn-out effort and butterflies usually do not congregate.
By May or June, most monarchs have returned to North America. Here their journey ends. The females lay their green eggs on milkweed plants, then die.
About one week later, the eggs break open to reveal a yellow, black and white-striped caterpillar. The caterpillar first eats its eggshell, after that it exclusively feeds on milkweed leaves.
Many types of milkweed contain a poison similar to digitalis. The poison is not toxic to the butterflies who actually store it in their body as a defense against predators. An animal that eats a monarch caterpillar or butterfly becomes ill and usually never tries to eat one again.
Predators quickly recognize the striped caterpillar and orange-and-black butterfly as something to avoid. Another butterfly, similar to the monarch, the viceroy, may deter predators because of its similar markings and colors.
The monarch caterpillar molts five times until it is about 2 inches long. The caterpillar then attaches itself to a plant or other object by a silk thread. After one day, the caterpillar skin splits open and the pupa, or chrysalis, form emerges. The pupa is shiny green with gold spots and a black and gold band. The caterpillar remains in the pupal case, undergoing the final metamorphosis into the familiar adult form.
Six weeks after its egg was laid, the adult butterfly breaks out of its chrysalis. This mature butterfly will complete the journey north, instinctively flying to a place it has never seen before. These adult butterflies may mate and establish another brood. As autumn approaches, the cycle continues as this new generation of mature monarchs migrates south.
Because of its migratory nature, the monarch butterfly needs food and habitat in its northern summer homes, along its fall and spring migratory paths, and in specific forest areas of Gulf of Mexico countries and states.
Roads, housing developments and agricultural practices can destroy important monarch habitat. Milkweed, their host plant, is considered a weed by some people and is often destroyed. Many monarchs and other butterflies are killed by pesticides. Simple steps like planting milkweed and other important wildflowers, as well as reducing the use of herbicides are actions that can help.
Monarchs are even more vulnerable at their winter sites. Eastern monarchs that migrate to Mexico, roost in trees that are valuable for lumber.
The monarch population has been declining for the last 10 years with significant drops in the population in each of the last three years. The number of trees and total area occupied by monarchs in the oyamel fir forests in Mexico was at an all-time low last winter — a mere 0.67 hectares.
A number of factors have contributed to this decline including:
- The use of herbicide-tolerant crops that eliminates milkweeds from agricultural fields;
- The increase in the planting of corn and soybeans for biofuels, often at the expense of milkweed-containing grassland and rangeland;
- Development of native grassland;
- Reduction of the edge area between roads and agricultural fields;
- Management of roadsides with herbicides and excessive mowing, which also eliminates milkweeds; and
- Deforestation of the oyamel fir forests that monarchs need to overwinter.
While some population fluctuations can be attributed to seasonal weather conditions, it is the decline of monarch habitat in the United States and Mexico that is the major concern. The good news is that monarch habitat can be restored in the United States and Canada by planting milkweed. Conservation organizations are also working with agencies and local groups in the United States and Mexico to restore or protect both breeding and wintering habitat.
To find out how to participate in monarch monitoring or create monarch habitat by planting milkweeds that are native to your area contact: Monarch Watch, email@example.com, 1-888-TAGGING, or www.monarchwatch.org.