Monarch Butterfly – Danaus plexippus

Monarchs are the most popular and best known butterfly in the US, Mexico, and Canada.  It is known for its migration to mountains in Mexico each winter.

The host plant for Monarchs is milkweed (Asclepias sp).  There are over 100 species of milkweed in the US.

The adult female butterfly lays her eggs on milkweed plants.

Monarch Laying Eggs

Female butterflies attach their eggs to leaves with a special ‘glue’. At Shady Oak Butterfly Farm, thousands of Monarch eggs are laid every week. In the wild, chances of finding more than one egg per leaf depends primarily upon the number of plants in the area. Females often lay eggs on young tender plants rather than in a patch of older plants. In the deep south, it isn’t unusual to find several eggs on one leaf.

Monarch butterfly eggs are small. When a butterfly caterpillar hatches from an egg, it is smaller than most people realize. People often forget that the caterpillar had to emerge from inside the egg. Caterpillars grow very quickly.

Eggs and a hatchling caterpillar are so small that they often are overlooked on milkweed plants. These eggs and this caterpillar are on a dime. When people hold a dime in their hands, they can imagine how small these caterpillars are when they begin life.

To hatch, a Monarch butterfly caterpillar must eat a hole in its egg shell. Once it has an opening large enough, it will crawl out of the egg shell. It normally turns around and immediately eats the rest of the egg shell. Although a Monarch caterpillar eats milkweed leaves, its first meal is its egg shell.

Butterfly farmers are concerned about the health of their caterpillars. Just as humans want their baby’s first meal to be germ-free, farmers want their caterpillar baby’s first meal to be germ free. At Shady Oak Butterfly Farm, all Monarch butterfly eggs are disinfected before the caterpillars hatch.

Young caterpillars are often hidden under milkweed leaves or in milkweed blooms. Monarch caterpillars of all ages often eat through a leaf vein to stop the flow of sap. Milkweed has a sticky thick white sap. This sap can harm a caterpillar by ‘gluing’ its mouth shut.

Monarch caterpillars eat leaves, flowers, seed pods, and sometimes the outer layer of milkweed stems. Milkweed, Asclepias species of plants, is the host plant for Monarch butterflies. Gardens with milkweed plants will attract Monarch butterflies.

Nearly every milkweed species will attract Monarch butterflies. Many gardeners buy and/or grow Tropical Milkweed, Asclepias curassavica. A milkweed that is grown in the deep south is Giant Milkweed, Calotropsis gigantea or Calotropis procera. In northern states, Common Milkweed, Asclepias syriaca, grows wild in huge patches. Some species of milkweed require many hours of freezing temperatures in the winter. Others, if exposed to freezing temperatures, may not grow back in the spring. Some species prefer damp or wet soil while other species of milkweed require dry sandy soil.

A Monarch butterfly caterpillar grows 2,500 times its original weight before it pupates into a chrysalis. This photograph shows a newly hatched caterpillar and one that is ready to J and pupate. That’s comparable to a human being the size of a semi before he/she becomes an adult.

A caterpillar has its skeleton on its outside. Although most people refer to the outside of a caterpillar as ‘skin’, it is actually its cuticle. Its cuticle is its skeleton. The cuticle never grows. It only stretches a small amount. When the cuticle has stretched as much as it can, the caterpillar lays a mat of silk from spinnerets under its head. It attaches its anal prolegs to the silk mat. After a day, the cuticle has loosened from the caterpillar and the caterpillar literally crawls out of its old cuticle. Underneath is a new larger cuticle.

When a Monarch butterfly caterpillar is ready to pupate, it lays another mat of silk and makes a tight button of silk in the middle of the mat. It attaches its anal prolegs (rear ‘legs’) into the silk button and, over the next couple of hours, drops into a J position. The next day it literally sheds its cuticle and is a soft chrysalis. Over the next hour the chrysalis reforms into its classic shape. During the next 24 hours, the outside of the chrysalis (its new cuticle) hardens. A Monarch chrysalis is jade green with gold dots.

One to two weeks later, depending upon the temperature, the wings of the butterfly show through the cuticle. When temperatures are extremely cool yet not freezing, the adult butterfly may take up to three weeks to emerge. The adult Monarch butterfly emerges the next day.

Its wings are tiny and soft when it first emerges. It immediately pumps hemolymph (insect ‘blood’) into its wings. The wings expand to their full size. Over the next half hour the wings will dry. Soon, if the weather is warm, light, and it isn’t raining, the butterfly will fly away.

Male Monarch butterflies have two dots on their hind wings. These are pheromone sacs/scales. Female Monarch butterflies have thicker black lines in their wings. Male Monarch butterflies are slightly larger, in general, than females. A few days after emerging, male butterflies begin their search for female butterflies.

Monarch butterfly numbers have declined in recent years. There are many causes of this decline. A few factors are, development, wide insecticide use, demand for bio-fuels, and Round-up Ready crops. We encourage everyone to plant milkweed to help the dwindling population. There is no danger of Monarch butterflies going extinct. They are found in many countries. In south Florida, there is a year-round population that never migrates. The primary concern is that the phenomenon of Monarch migration may be at risk.

Monarch Watch, a program of the University of Kansas, has a tagging program to help scientists discover more about the eastern Monarch butterfly migration. Small sticky dots with identification information on them, are placed on butterflies by Monarch enthusiasts throughout the United States. A few tags are recovered in Mexico and the identification tag numbers are sent to Monarch Watch. Documentation is checked to determine where the butterflies were tagged and released. Both wild butterflies and farmed butterflies are tagged. Documentation includes the information of whether the butterfly was male or female, farm raised or wild tagged, and from where it was released.