Monarch Butterfly

Genus:  Danaus
Species: plexippus

Brilliant orange and black monarchs are among the most easily recognizable of the butterfly species which call the Americas home. Their migration takes them as far north as Canada and, during the winter months, as far south as Mexico City. A single monarch can travel hundreds to thousands of miles!

Monarchs are truly spectacular migrants, because the butterflies know the correct direction to migrate even though they have never made the journey before. They follow an internal "compass" that points them in the right direction each spring and fall. The monarch migration is one of the greatest natural phenomena in the insect world.

Monarch butterfly

Description: 

Monarch butterflies are bright orange with black and white markings. The body of the monarch is black. The head has a set of antennae.

The wings are mostly orange with black veins running throughout. The outer edge of the wings has a thick black border. Within the black border are white spots. The white spots can range in size and they decorate the wings. At the upper corner of the top set of wings are orange spots.

The underside of the monarch butterflies' wings can be seen when the butterfly is at rest or when it is feeding on a flower. Instead of bright orange, the underside is more drab and orange-brown.

Males and females can be told apart by looking at the top of their hind wings. Males have a black spot at the center of each hind wing, while the females do not. The spot is a scent gland that helps the males attract female mates. Another less accurate way to tell males from females is that the females usually have much thicker veins than the males.

Monarch butterfly caterpillars are also easy to identify. The caterpillars have many yellow, black and white bands. There are antenna-like tentacles at each end of the caterpillar's body.

Size: Monarch butterflies have a wingspan of 3 1/2 - 4 inches.

Diet:  Monarchs, like all butterflies, change their diet as they develop. During the caterpillar stage, they live exclusively on milkweed plants. Milkweeds are wildflowers in the genus Asclepias. Milkweeds contain glycoside toxins that are harmless to the monarch but poisonous to its predators. Monarch caterpillars feed on all the different parts of milkweed plants and store up the toxins in their body. The toxins remain in their system even after metamorphosis, thereby making adult monarchs poisonous as well.

Adult monarchs feed on nectar from a wide range of flowers, including milkweeds. 

Typical Lifespan:  Most monarch butterflies do not live more than a few weeks. There are about 3 to 5 generations born each spring and summer and most of the offspring do not live beyond 5 weeks. The lone exception is the last generation born at the end of the summer.

The last generation of each year is the over-wintering generation that must make the journey back to Mexico. Rather than breeding immediately, the over-wintering monarchs fly back to Mexico and stay there until the following spring. In the early spring, they fly north to the southern United States and breed. Over-wintering monarch butterflies can live upwards of 8 months.   

Habitat:

Monarch butterflies utilize different habitat in the warm months versus the cold months. In the spring, summer and early fall, they can be found wherever there are milkweeds. Monarchs lay their eggs on milkweeds and they're always searching for them in fields, meadows and parks. Many people plant milkweeds in their gardens.

Monarchs cannot survive freezing temperatures, so they over-winter in the cool, high mountains of central Mexico and woodlands in central and southern California.

Range:  Monarch butterflies can be found throughout the United States, including Hawaii.

The majority of monarch butterflies live east of the Rocky Mountains. In the early spring, they are first seen in Texas and the south. As spring turns to summer, they're seen in more and more states and Canada.

A much smaller population of monarch butterflies lives west of the Rocky Mountains. Instead of making the long journey between Mexico and Canada, the western monarchs only travel as far south as San Diego. Some monarchs live in California year-round and others spend summers as far north as British Columbia, Canada.

Hawaii also has monarch butterflies. Monarchs that were released or lost their way from California have found success year-round on the Hawaiian Islands.

Communication:

Monarch butterflies communicate with scents and colors.

  • The males attract females to mate by releasing chemicals from scent glands on the hind wings.
  • All monarchs signal that they are poisonous by having bright orange wings. The bright colors serve as a warning that predators should attack at their own risk. 

Life History and Reproduction:

Over-wintering monarch butterflies in Mexico begin to make the journey north to the United States in early spring. Soon after they leave Mexico, pairs of monarchs mate. As they reach the southern United States, females will look for available milkweed plants to lay eggs.

The eggs hatch after approximately four days. The caterpillars are small and they grow many times their initial size over a two-week period. The caterpillars feed on the available milkweed plant. When they get big enough, each caterpillar forms a chrysalis and goes through metamorphosis.

The chrysalis protects the monarch as it is going through the major developmental change of turning from a caterpillar to a butterfly. The chrysalis is green with yellow spots. After another 2-week period, an adult butterfly will emerge from the chrysalis.

The adult monarchs continue the journey north that was left unfinished by their parents.  Each year, about five generations will be born to continue migrating north. It is only the last generation, born in late summer that will live eight months and migrate back to Mexico to start the cycle over again.

Threats to Monarch Butterflies:

  • Global Warming  - Climate change alters the timing of migration and rainfall patterns in their forest habitat.
  • Habitat Loss  - In the United States and Mexico. 
  • Forest Fragmentation
  • Pesticides  - Chemicals kill their milkweed food.
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