Monarch Butterfly Caterpillar: Everything You Need to Know

Written by AZ Animals Staff
Published: January 4, 2022
Image Credit iStock.com/CathyKeifer
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For centuries, humans have been enthralled by the monarch butterfly. This milkweed butterfly is not only beautiful with its bold orange and black colors but undergoes an unusually strenuous and fascinating migration that can take several generations to complete. This means a butterfly from New York can start its journey to Mexico even though its great great great grandchild might be the one to finally arrive. Another of the amazing facts about this butterfly is even its larva, caterpillar, and its chrysalis are beautiful — something that can’t be said for most butterflies. Monarch butterfly caterpillars are also completely harmless, with no stinging spines or hairs, and people often raise them until they complete the stages of their metamorphosis.

The lifecycle of the monarch butterfly is like all other butterflies and many other insects. It undergoes a complete metamorphosis, which means that it starts off as a larva, turns into a pupa then emerges from the pupa as an adult animal that looks nothing like its larval form. Here are some facts about the monarch butterfly caterpillar.

The monarch butterfly caterpillar has beautiful black, yellow, and white stripes along its body.

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How to Identify Monarch Butterfly Caterpillars

Identification of the grown monarch caterpillar is easy. Even people who only superficially know about caterpillars can recognize the caterpillar of the monarch butterfly. It is a medium-sized, plumpish caterpillar that comes with white, black, and yellow stripes and looks like no other. Not even the caterpillar of its cousin the Queen butterfly, whose colors are similar but whose pattern is different, can be mistaken for it.

The caterpillar, like most, needs to go through stages before it is ready to pupate. These stages of the caterpillar’s life cycle are called instars.

The first instar is the one that hatches from the egg. Identification of the larva at this stage can be tricky, as it doesn’t look like the archetypal monarch caterpillar. It is shiny, translucent pale green, has a black head, and does not have the diagnostic black, yellow, and white colors. It first eats what’s left of its egg then starts to eat the host plant, which is nearly always milkweed. It’s between 0.08 and 0.24 inches in size.

It’s only when the first instar molts that the stripes appear. There’s also a yellow triangle surrounded by yellow bands on the head. The caterpillar’s two pairs of tentacles, one pair at the thorax and one pair on the abdomen, are beginning to grow. This caterpillar is between 0.24 and 0.39 inches in size.

After the third molt, the tentacles are longer. Biologists believe these tentacles are sensory organs, even though the caterpillar does have tiny antennae. The stripes or bands are more distinct, and the caterpillar is between 0.39 and 0.59 inches long. The fourth instar caterpillar has grown white spots on its back and is now between 0.59 and 0.98 inches in size.

The colorful bands on the fifth instar are more complex, and it has grown tiny front legs near its head. Nourished on its diet of milkweed, the caterpillar can grow to as much as 1.96 inches in length. When it gets to be as big as it’s going to get, the caterpillar stops eating and starts looking for a place to pupate and continue its life cycle.

Where Are They Typically Found?

The monarch butterfly, Danaus plexippus, is found in North America. Its habitats include empty lots, roadsides, wet meadows, gardens, marshes, pastures, and open areas. In other words, it shares the same habitat as the milkweed plant.

The monarch butterfly caterpillar feeds on milkweed.

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What Do They Eat?

Milkweed is a staple of the monarch caterpillar’s diet, to the point where it and its cousins are called milkweed butterflies. The butterfly’s life cycle begins when the female carefully lays her eggs on a leaf of the plant, one at a time, securing them with a bit of natural glue. Other than that she doesn’t provide any parental care. Over about a month, she can lay as many as 500 eggs. When the caterpillars hatch, they eat their egg case then start to eat the leaves.

The leaves of milkweed plants are toxic to many animals, but the monarch butterfly caterpillar can store the toxins in its body, and they are still present when it hatches as a butterfly out of its chrysalis. The butterfly’s strong colors warn potential predators that it is poisonous.

Other plants that make up the monarch caterpillar’s diet are wild carrots, thistles, asters, coneflowers, boneset, Joe-Pye weed, goldenrod, lilacs, red clover, alfalfa, and other plants that like a somewhat wet habitat.

How to Raise Them

Raising monarchs is easy and fun. Not only this, it benefits the butterflies, whose conservation status is near threatened. They have even been successfully raised aboard the International Space Station.

The first thing to do before anything else is to establish some milkweed in the garden or find a reliable stand of some outdoors. Then, buy two containers. They do not have to be large, but the first needs to be large enough to hold the eggs and the first and second instars. The second needs to be large enough to hold the mature caterpillar, its chrysalis, and the adult after it emerges. Check the milkweed plants during their growing season for eggs. If there’s an egg on the leaf, cut the leaf off, and bring it inside. You’ll never need to touch the caterpillar at all while it’s in your care.

Line the first container with a paper towel, mist it with water, then place the leaves on top of it. Shut the top of the container, and put it in bright light but not in full sunlight. Make sure to keep each container clean, including removing the soiled paper towels, and feed the caterpillars milkweed leaves daily. When a caterpillar is ready to pupate, it will move to the top of the container. There it will attach itself, hang in a J shape for half a day then split its skin to reveal the chrysalis.

The identification of the monarch chrysalis is also easy. It is a beautiful light green dotted with gold at the top and bottom. It will hang for about two weeks, then turn transparent just before the butterfly emerges. It will take between three and four hours for the insect’s wings to harden, and the container should be big enough for it to flap its wings when the time comes. After that, it can be released. If the weather is inclement, the butterfly can be kept overnight in a flight cage.

The one caveat about rearing monarch caterpillars is that the adults do not seem to migrate as successfully as wild butterflies.

The monarch butterfly caterpillar takes about three to eight days to incubate.

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How Long Do They Incubate?

The incubation of monarch butterfly eggs takes about three to eight days. It takes a caterpillar a little less than a month before it’s ready to pupate. Pupation takes about eight to 15 days.

When Do the Breeding and Hatching Seasons Typically Take Place?

Breeding and hatching of the monarch usually take place in the spring and summer.

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AZ Animals is a growing team of animals experts, researchers, farmers, conservationists, writers, editors, and -- of course -- pet owners who have come together to help you better understand the animal kingdom and how we interact.