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The Monarch Butterfly: The State Insect of Illinois

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The monarch butterfly is the state insect of Illinois.

The monarch butterfly is the state insect of Illinois.

This article is about the state insect of Illinois, the monarch butterfly. Illinois designated the butterfly as its official state insect in 1975. As is the case in several state-insect decisions, the campaign was pushed forward by schoolchildren from an elementary class. It's reported that a third-grader from Decatur was the first to suggest the monarch as a state insect candidate.

Several other states have chosen the monarch as their state insect or butterfly, and for good reason—they are beautiful, widespread, and known for their spectacular migrations.

The magnificent Monarch may be the most well-known and best-loved of all our insects. There is something truly regal about its size, bright colors, and powerful, soaring flight, but its kingly name supposedly comes from the spotted margins of its wings, which resemble the sable-edged robes worn by royalty at the time of its discovery.

Nearly everyone has seen monarchs and is familiar with their mind-boggling migrations and million-butterfly roosting in the mountain forests of Mexico. But there are more reasons to be fascinated with this species. For one thing, it is thought that the poisonous sap in milkweed, the monarch's only food source, makes it distasteful to predators like birds. Milkweed plants are very common in Illinois.

Monarch Basics

  • Scientific/taxonomic name: Danaus plexippus
  • Food source: Milkweeds
  • Threat to plants and trees: None
  • Status: Not rare or endangered but under threat from industrialized agriculture
The spotted margins of monarch wings resemble the sable-edged robes worn by royalty at the time of its discovery.

The spotted margins of monarch wings resemble the sable-edged robes worn by royalty at the time of its discovery.

Taxonomy

Illinois' state insect belongs to Nymphalidae, a very large butterfly family that is distributed around the world from chilly northern regions to steamy tropical zones. Monarchs and their relatives are in the subfamily Danainae. In the U.S., there are only two common representatives of this group: the monarch and the queen. The queen is darker and less well-known than the bright orange monarch.

The scientific name of the monarch butterfly is Danaus plexippus. That means the genus is Danaus and the species is plexippus. Scientific names are always stylized in italics.

Monarchs feed exclusively on the poisonous sap of the milkweed plant.

Monarchs feed exclusively on the poisonous sap of the milkweed plant.

Why Are So Many Butterflies Orange Like the Monarch?

The state insect of Illinois is colored brilliant orange and black, especially the male. There may be a very good reason why so many butterflies are orange—they have evolved to resemble the monarch so birds will think twice before eating them even if they are perfectly edible. This is the idea behind mimicry, and if the theory is accurate, then the monarch is not only big and beautiful but highly influential as well.

This diagram illustrates the complete metamorphosis of butterflies and beetles.

This diagram illustrates the complete metamorphosis of butterflies and beetles.

Complete Metamorphosis

"Complete metamorphosis" is the term used to describe the life cycle of insects that go through a four-stage sequence of forms. For butterflies, this means egg-larva-cocoon/chrysalis-adult. It helps to take the butterfly as an example, although dragonflies, bees, wasps, flies, beetles, and many other insects also go through complete metamorphosis. Like butterflies, they all spend time as larvae and all of the other developmental stages.

The monarch butterfly is typical of the insects that undergo complete metamorphosis. The egg is laid on the food plant, and the caterpillar that hatches out eats the leaves of the plant. As it grows, it sheds its skin in a process known as molting. The stages between molts are called instars, and after the last instar, the caterpillar sheds its skin for a final time.

The last time the caterpillar sheds its skin, it enters the cocoon/chrysalis phase, known by scientists as "diapause." It's also called a "pupa." Inside the pupa, the insect's cells break down into a kind of goop and then rearrange and reassemble to form the body and wings of the adult butterfly or moth.

The final "instar" occurs when the insect hatches out of the pupal skin, at which point it is ready to mate and continue the cycle. The adult feeds just enough to achieve its goal of mating and laying eggs; Beyond that, it has no additional purpose in its adult form.

Monarch caterpillars are just as visually stunning as their adult counterparts.

Monarch caterpillars are just as visually stunning as their adult counterparts.

The Monarch Butterfly's Fascinating Caterpillar

The caterpillar of the monarch butterfly should be familiar to anyone who has looked for insects around milkweed plants. You will never find this species on anything other than some kind of milkweed (Asclepias species). Many insect species are tied to a particular plant, and the monarch is no exception.

If you have ever broken a leaf off of a milkweed plant, you will see where the plant gets its common name -- white sap will quickly begin to ooze from the broken stem. Also known as latex, sap like this contains toxic alkaloids that protect the plant from most animals and insects that might eat the leaves. However the monarch, and a few other insect species, have adapted to the poison. They eat the leaves and, it's thought, some of the poison works into their system and makes them toxic too. In this way they may be protected from being eaten by a predator.

This graphic illustrates the migration of the monarch.

This graphic illustrates the migration of the monarch.

The Monarch's Amazing Migration

Much has been written about the annual movement of millions of adult monarch butterflies from their overwintering areas in Mexico to much of the temperate zone of North America. Between March and November, monarchs are on the move. This happens over the course of several overlapping broods as the insects lay eggs, which develop into adults and continue to expand northward. The monarchs you see in your garden in the spring are on the move toward Canada; those floating in the air in the fall are on their way south as their range contracts.

You can help sustain the monarch population (and attract beautiful butterflies to your home) by planting milkweed—their food source—in your garden.

You can help sustain the monarch population (and attract beautiful butterflies to your home) by planting milkweed—their food source—in your garden.

Help Sustain the Monarch Population by Planting Milkweed

Milkweed is a native plant that grows almost anywhere, although commercial pesticides and careless land use have made it less common than it was, even very recently. For this reason, monarch numbers are dwindling at an alarming rate. The state insect of Illinois depends on milkweed! Please help this magnificent animal by planting and nurturing milkweed plants in your garden or yard.

Resources and Further Reading

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.