By Sam Burbach, Education & Programming Coordinator – 07/15/2020

 

Table of Contents

Week 1
Week 2
Week 3
Week 4

Join us over the next couple weeks as we follow the life cycle of a monarch butterfly! Monarch butterflies are one of the most well-known butterflies and happen to be the Illinois State Insect (designated in 1975); as well as the state insect or state butterfly of six other states! It makes sense that monarchs are the state insect/butterfly of several U.S. states as they are native to North and South America.

We will begin to view the monarch life cycle from an egg. Female monarch butterflies lay their eggs exclusively on milkweed plants because that is the only food source for the larvae, more commonly known as caterpillars.

The caterpillar will emerge from the egg in 3-5 days and begin munching away at milkweed leaves. Milkweed plants contain toxic cardenolides in their sap, which monarchs are tolerant of. By consuming milkweed, monarch caterpillars and adult butterflies store the toxin in their bodies which makes them poisonous to predators. It is a great defense system!

Week 1

If you’d like to provide habitat for monarch butterflies, you should start by planting some milkweed so that the butterflies will have a place to lay their eggs. Two types of milkweed that Klehm has on our property are common milkweed (Asclepias syriaca) and butterfly weed (Asclepias tuberosa).

Once you have some milkweed planted, or happen to see some while visiting Klehm or other spaces, check for monarch eggs or caterpillars by gently inspecting the leaves. Eggs are laid singly and are usually found on the underside of leaves. Eggs are sometimes hard to spot as they are so tiny, usually just the size of a pinhead. They are an off-white color and an elongated oval shape, with ridges running from the top to the bottom, resembling a barrel.

While the eggs can be sometimes hard to find, they do stand out against the leaf with their color. The newly hatched caterpillars can be very hard to find as they are so tiny having to fit in that egg! Their stripes are present but hard to distinguish and their black head is what contrasts against the leaf most. As the caterpillars grow they will become easier to find with some patient inspection of milkweed leaves.

Here you can see a monarch egg and a newly-hatched caterpillar. This caterpillar emerged from its egg somewhere from 0-12 hours prior to this photo.

Come back next week as we watch this caterpillar (and its soon to hatch friend) grow and explore more of the monarch life cycle!

Week 2

Today we check in on our monarch caterpillar a week after hatching. Monarchs spend approximately two weeks in the larva stage. During this time, the caterpillar feeds on milkweed leaves to grow, increasing its mass approximately 2,000x from the time it hatched to when it enters the next phase of its lifecycle. The caterpillar will shed its skin as it grows and goes through five stages, known as instars, between each of these molts. The yellow, black, and white stripes that make monarch caterpillars easy to identify become clearer in each instar.

Caterpillars in the larva stage are still true insects, and being insects, they have three distinct body segments, two antennae, and six legs. You might be thinking, “I only see one body segment,” “I see four antennae,” and/or “I see way more than six legs!” Let’s take a closer look at monarch caterpillar anatomy.

A caterpillar might look like a single body segment, but there are three separate parts. The head is small and can be found at the end with the two longer “antennae,” but the truth is, the two pairs of what looks like antennae on either end of the caterpillar are not actually antennae. The true antennae are very small and hard to see with the naked eye. They are located on the front of the head near the mandible mouthparts and aid in smelling to guide the caterpillar since they have poor eyesight, despite having six pairs of simple eyes called ocelli. 

The four black things that we would think of as antennae are actually tentacles which function as sensory organs to help the caterpillar navigate.

Getting back to body segments, the next section behind the head is the thorax. This body segment is where the six true legs are attached. Insects’ true legs have joints and will remain present in the adult insect. These six true legs are not the primary body parts responsible for helping the caterpillar move around though. The stumpy looking legs, called prolegs, attached to the final body segment, the abdomen, are responsible for helping the caterpillar move around. Monarch caterpillars have five pairs of prolegs with each proleg having a pad covered in tiny barbs or hooks called a crochet. The crochets help the prolegs attach to a leaf, stem, twig, etc. so that the caterpillar can propel its body forward. These prolegs will disappear as the monarch goes through metamorphosis and will not be present on the adult butterfly.

Let’s review – monarch caterpillars have:

  • 3 body segments that look like 1
  • 2 antennae that we cannot even see
  • 4 tentacles that look like antennae
  • 6 true legs that barely contribute to moving around
  • 10 prolegs that greatly contribute to moving around but will disappear on the adult butterfly

Phew! Who knew caterpillars could be so complex! Next time you see a monarch caterpillar, see if you can notice any of these distinctions, and next week we’ll check in to see how this caterpillar has grown after another week!

Week 3

It has been two weeks since our caterpillar emerged from its egg and its growth has been exponential! This caterpillar has been munching away on fresh milkweed preparing to form its chrysalis. While caterpillars may seem small, they can go through a lot of milkweed.

Raising and caring for caterpillars is relatively simple, and a great way for kids to learn about complete metamorphosis in insects.

If you would like to try and raise some caterpillars of your own, here are a few things to keep in mind:

  1. Wash hands before and after caring for your caterpillars and try not to touch the caterpillar if possible.
  2. Search for monarch eggs and caterpillars locally.
    • It is important that monarchs are raised and released close to where they were found outside.
  3. Always start with a clean habitat that has good ventilation.
    • Mesh pop-up habitats have become popular for raising butterflies in and are very easy to find for purchase. A mesh enclosure ensures good air circulation and gives you a great view of the caterpillars being raised. A plastic container or aquarium tank can also be used, but make sure the covering is mesh so there is good air flow.
    • The enclosure should be cleaned daily to remove frass (caterpillar poop!) and wilting and/or chewed up milkweed. Placing paper towels, cardboard, or something to catch the frass on in the bottom of the enclosure will make cleaning easier.
    • Between caterpillar broods, sanitize the enclosure with a 20% bleach solution.
  4. Provide fresh milkweed often.
    • Collect milkweed locally and only use sources of milkweed that you know are free of pesticides.
    • Cut a long section of milkweed and inspect the cutting for any hitchhikers. Remove any insects, such as aphids or ants, and any egg masses that are not monarch eggs, so you do not introduce them to your habitat.
    • Milkweed sap will drip from the cut stem and any places you have removed or torn any leaves. Before placing the milkweed in a vase of water, thoroughly rinse the cut end of the stem in warm water to wash away any of the sap – the sap can clog the stem causing the milkweed to wilt faster.
    • Cover your vase or jar of water with plastic wrap and poke the milkweed stems through to make sure the caterpillars cannot accidentally fall into the water.
    • Inspect old milkweed in the habitat for caterpillars and eggs. If a caterpillar or egg is still on a particular leaf that is past its prime, carefully remove that leaf and lay it on some fresh milkweed for the caterpillar to crawl onto.
  5. Do not raise too many caterpillars at once and watch for signs of disease.
    • Only raise a couple of caterpillars at a given time. This will lower chances of insufficient food supply and potentially spreading disease.
    • If a caterpillar looks sick (discolored, limp, inactive) or an egg turns black and does not emerge within three days, remove it so that it does not spread disease.
  6. Once a caterpillar is in its chrysalis it will not need food.
    • If you can clean your enclosure without disturbing the chrysalis, you can carefully remove the milkweed and clean the last of the frass out. If your caterpillar made its chrysalis on a piece of the milkweed you can carefully remove the rest of the milkweed and just save the piece with the chrysalis on it.

Our caterpillar friend should be making its chrysalis in the next couple of days, so we will check back in and discuss the chrysalis stage next week!

Week 4

As we check back in on our monarch this week, it looks quite different than before. After spending 17 days munching on milkweed, this caterpillar entered the next stage of metamorphosis which is the pupal stage. This stage is rather magical, where we will see our friend change from a caterpillar to a butterfly.

After a caterpillar has spent approximately two weeks in the larval stage, its body will prepare to shed its skin one last time to reveal the pupa. The pupa of a butterfly is known as a chrysalis, not to be confused with a cocoon.* The chrysalis is a hardened outer shell of a butterfly pupa. It forms under the skin of the caterpillar before its final molt. Prior to molting, the caterpillar will crawl to a protected area and attach itself to the underside of a twig, leaf, or in our case the top of the butterfly enclosure, with a silk button. Once secure, the caterpillar will hang upside down in a “J” shape for approximately 18 hours. Once the caterpillar is ready to enter this next stage, its skin will split near the head and the pupa will wiggle around to shed the larval exoskeleton one final time. The chrysalis will dry and harden over the next few hours.

Take a look at this video of a caterpillar going into its chrysalis from last summer for a better idea of what this process looks like!

*So what exactly is a cocoon? A cocoon is an external structure made by larvae as a form of protection during the pupal stage. The pupa of insects that build cocoons does not harden the way a chrysalis does so the larva will spin a cocoon around themselves made of silk and sometimes various other materials, such as leaves or plant matter, which will harden for protection. Once the cocoon is constructed, the larva will pupate within the cocoon. Many insects who go through complete metamorphosis create cocoons, such as ants and wasps, however we mostly associate cocoons with moths.

The pupa may seem like it is in hibernation, not eating or even moving, but inside the chrysalis the body is completely changing. A monarch will spend approximately 8-14 days in its chrysalis. While in the pupal stage, it’s body makes many major changes. The most obvious change is the appearance of wings, but the presence of wings also requires a whole new set of muscles to allow for flying. The legs and antennae also lengthen, the body segments become more obvious, the 12 poor-vision larval eyes (ocelli) become two compound eyes with true color vision, and the chewing mouthparts become a proboscis which acts like a straw, thus changing the insect’s diet from leaves to nectar. Other changes and developments also take place during this phase, making the time spent within the chrysalis quite eventful even though it doesn’t look like anything is happening.

We’ll check in on our monarch again in about a week when it emerges as an adult butterfly!