The monarch—easily recognized by dark orange wings with black veins and white edge spots—is found throughout the United States and into southern Canada. This butterfly is also one of the few that migrate.
As the days grow shorter, the fall migration begins with millions of monarchs making their way south. Monarchs in the west migrate to southern California, while those in the central and eastern parts of North America overwinter in the Gulf States and remote mountain valleys of south-central Mexico.
From the first week of September through the third week of October, this familiar 4-inch beauty is making its way south through the Chesapeake Bay watershed.
These social creatures tend to congregate at the onset of migration and at rest sites along the way. Like migratory birds, the butterflies follow shorelines and mountains.
High points and fields afford good views to watch them pass. When winds are light, areas popular for watching hawks or other migrating raptors—such as Hawk Mountain in Pennsylvania—are also popular with monarchs.
When winds come from the south, monarchs stay close to the ground, using landscape features to protect themselves against oncoming winds. Taking advantage of northerly tail winds, monarchs remain high in the sky and fly due south. At night, the butterflies may congregate together on trees. Monarchs sometimes rest on narrow-leaved trees like willows and pines.
Most peninsulas on both the eastern and western shores of the Chesapeake Bay 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 often attract monarchs. Migrating monarchs often stop and rest at these and other southern tips before crossing water.
The butterflies are only passing through the Chesapeake Bay area, though, on their arduous flight. By November, they have usually reached their winter destinations, sometimes 2,000 miles away. The insects 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. After they have mated, the butterflies—mostly females—are ready to return north. Only 1 percent of the monarchs survive to begin the spring flight. This migration is not as spectacular as the fall migration. It is a long, drawn-out effort and the butterflies usually do not congregate.
By May or June, most of the monarchs’ northern journey come to an end. The females lay their green eggs on milkweed plants and then die.
About one week later, the eggs break open to reveal a yellow, black and white striped caterpillar. The caterpillar will first eat its own eggshell, then eat the leaves of its food plant.
Monarch caterpillars feed exclusively on milkweeds. Many types of milkweed contain a poison similar to digitalis. The poison is not toxic to the monarchs, though, who actually store it in their bodies.
This poison serves as a chemical defense against predators. A bird or other animal that eats a monarch caterpillar or butterfly becomes ill and will usually never try eating one again. Predators quickly recognize the striped caterpillar and orange and black butterfly as something to avoid.
Another similar butterfly, the viceroy, may deter predators because of its apparent mimicry of the monarch’s 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 weaving 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. Using hooks, the pupa attaches to the silken thread and the rest of the caterpillar skin drops off. 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. 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 their migratory nature, the monarch needs food and habitat in its northern summer homes, along its fall and spring migratory paths, and in specific forests in the states and countries bordering the Gulf of Mexico.
Monarchs are threatened by human activities, in both their summer and overwintering sites. In the United States and Canada, roads, housing developments and agriculture 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 and reducing herbicide and pesticide use help monarchs.
Monarch populations are even more vulnerable in their overwintering sites. Eastern monarchs that migrate to the Mexico roost in trees valued for their lumber. Logging not only removes roost trees, but also opens up the forest canopy. These gaps let in snow and rain, making monarchs vulnerable to freezing.
Conservation organizations are working with government agencies and local groups to protect land, sponsor research, educate the public about monarch conservation and develop alternative economic choices in the region.
Kathy Reshetiloff is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.
Monarch Butterfly Groups
For information about conserving monarch butterflies contact:
Monarch Butterfly Sanctuary Foundation
c/o Karen Oberhauser
2078 Skillman Ave W
Roseville, MN 55113