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14.2: Danaus plexippus: Monarch Butterfly

Difficulty Level: At Grade Created by: CK-12

Common Name

  • Monarch Butterfly
  • Milkweed Butterfly


The monarch butterfly has a black outline, and inside of the black border is orange color. On the edge there are white dots. Altogether, it looks like a stained glass window. The monarch weighs between .0095 to 0.026 ounces and is about 4 inches wide when the wings are open.

Man affects the monarch butterfly by using the fields and meadows that they live in to make buildings, so the butterfly’s home is taken away.

The complete taxonomic classification is:

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Lepidoptera
  • Family: Nymphalidae
  • Genus: Danaus
  • Species: D. plexippus


The monarch butterfly population is split into two sides of the United States; the two sides are the east and west of the continental divide. They live in milkweed plant communities. They live in places with warm temperatures. The population on the eastern side spends its winters in Mexico, and the rest of the year in the United States and Canada. In winter they can be found in high altitudes in Central Mexico. The population on the western side of the continental divide can be found in Idaho, Utah, Arizona, Colorado, and California in the summertime. At the end of summer the butterflies migrate back towards the coast, and they stay in areas ranging from Baja to San Francisco. When they migrate, they look for big tall trees like eucalyptus trees. During the winter, the butterflies live on moisture and body fat until milkweed grows again in the spring, and then they fly inland.


There are four stages in the life of the butterfly. The four stages are:

1. Egg: The first stage is an egg. This butterfly will only lay it’s eggs on milkweed plants.

2. Larva: The second stage is when the caterpillar hatches from the egg. It is hard to see at first, but later within two weeks it gets to be a few inches long. Usually the caterpillar has stripes or a pattern on it of yellow and black, and it has to keep shedding about 4 or more times. Caterpillars need to eat a lot.

3. Pupa: After the caterpillar has grown to a certain size, it makes itself into a light green chrysalis and changes inside.

4. Adult: The last stage is the butterfly stage. Adults reproduce in this stage.

Cell Biology

Like all other plants and animals, the monarch butterfly has eukaryotic cells. Eukaryotic cells have a nucleus and many other organelles. New cells are made when existing cells grow and divide. Some reasons cells divide are that they have to repair tissue, growth, or reproduction.  Mitosis  happens when the nucleus of the cell divides, and two new cells with the same DNA as the original one are formed. 

Meiosis is cell division in which gametes (example: egg, sperm) are made with half the chromosomes of the original cell.  Chromosomes are made of DNA with genes that have “codes” for the butterfly’s traits.  


Scientists say that the butterflies separated from moths 150 million years ago.  Butterflies are in the moth family.


Some predators of the monarch butterfly are wasps, bees, snakes and birds. The predators who eat the monarchs won’t want to eat them again because they don't like the taste. The monarch butterfly eats the milkweed plant (as a caterpillar), which gives the butterfly a strange taste to its predators. The predators don’t like the strange taste.  Their unique color of orange and black make them stand out and will keep predators away. The bad taste, together with the bright colors provide a successful defense mechanism. Monarchs share the defense of bad taste with the similar-looking viceroy butterfly in what is perhaps one of the most well-known examples of mimicry. Mimicry is the similarity in appearance of one species to another which protects one or both of them.

This butterfly will only lay it’s eggs on milkweed plants, which becomes a food source for the caterpillar as the eggs hatch.

When monarch butterflies on the West Coast of the United States come south towards southern California, to area such as San Diego, they search for big trees like Torrey pines, redwood and eucalyptus trees. 

Anatomy and Physiology

The main parts of the butterfly are the head, thorax ( the section of the body that binds the abdomen and the head) and the abdomen. Other parts include the leg, fore wing, hind wing, wing veins, compound eye, proboscis (long mouth part), and antenna.


In the fall, monarch butterflies migrate in millions from north to south. In the spring, they migrate from south to north. Monarchs stay in groups when they migrate. The monarch butterfly is the only butterfly that migrates both north and south as birds do regularly.




  • Janae N. Beasley
  • Natalie Vollmer
  • Quinn Tribolet

Supervising Faculty

  • Amy Huff Shah


  • Museum School, San Diego, California


  • Published prior to review.

Edit History

  • Created: April 5, 2013
  • Version 1.0 submitted to CK-12: July 5, 2013
  • CK-12 edits: in progress


  • Middle School (grades 6-8)

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Date Created:

Aug 15, 2012

Last Modified:

Dec 05, 2014
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