How to Raise Monarch Caterpillars

 Director's Note: Our two seasonal naturalists for 2020, Katherine Culbertson and Jack McDonough, are preparing a series of blog posts designed to educate readers about many aspects of monarch biology and related topics.  Here's the fourth of this series, written by Katherine Culbertson, and titled: 

How to Raise Monarch Caterpillars

In our previous educational blog post, we talked about the monarch’s life cycle; if you want to watch this fascinating process up close, it’s easy to raise your very own monarchs. In fact, many elementary school science classrooms hatch out monarch and other butterflies to teach kids about metamorphosis, but you’re never too old to witness this magical process. Below is all the information you need to get started!

• A few key things to remember before bringing monarchs home:
• Monarch caterpillars ONLY eat milkweed, and must always have fresh food
• Monarchs must be in a naturally lit area (but not in direct sunlight) for them to properly develop; a shaded porch is ideal, but an indoor room with natural lighting can work in a pinch
• It will take about 4 weeks for your monarch eggs to turn into an adult butterfly
• Be sure to release your monarchs close to where you found them! (i.e. Please do not bring them to Cape May to release if you didn’t find them here.)
• It is inadvisable to raise large numbers of monarchs; just a few give you chances to observe the whole process of growth and metamorphosis.

You will need:

• Bug box, aquarium tank, or similar container with good airflow
• Milkweed cuttings – be sure to collect the same variety you found your caterpillar(s) on
• Either: 
• (1) A small bottle or similar container filled with water (to put milkweed in) AND Plastic wrap or foil (to cover water so that caterpillars don’t fall in!) 
• OR
• (2) Wet paper towels

Before you collect your monarch caterpillars, be sure you have a secure place to keep them with good airflow. Caterpillars are escape artists, so there cannot be any gaps small enough for them to fit through. A bug box or aquarium with a mesh lid makes a good home for caterpillars, as does a mesh butterfly cage. Be sure to place your caterpillars’ new home in a place with natural lighting, but not in direct sunlight.

The best place to find your monarch eggs or caterpillars is in your garden, or another milkweed patch close to your home. There are three species of milkweed that you can find monarch eggs on near Cape May – swamp milkweed, common milkweed, or butterfly weed. (If you live outside of Cape May, check what milkweed varieties grow in your area!) Caterpillars or eggs can be found on milkweed plants from May to October. Check the small tender leaves at the top of plants especially well – female monarchs often prefer laying eggs on these leaves. Eggs can be tricky to find, as they are only about the size of the head of a pin! They are off-white in color, and are always laid individually; if you spot a cluster of eggs, they are definitely not monarch eggs. The best way to spot tiny caterpillars is to look for small holes in milkweed leaves, where they have just begun to eat.

If you find a leaf with an egg on it that is close to the top of a milkweed plant, if is best to snap off the entire top of the plant and stick it in water (see below), as this will keep the leaves fresh until the egg hatches. If this isn’t possible, break off the leaf and wrap the end in a wet paper towel, making sure to moisten it twice a day and provide fresh leaves as soon as the caterpillar hatches (which may take up to 4 days). 

For the next two weeks, as your caterpillar(s) grow, it is important that they always have access to fresh milkweed. There are two ways you can do this:

(1) Cut off the top of a milkweed plant and place it in a bottle or similar container filled with water (the same way you would place a bouquet of flowers in a vase). Be sure to cover the gap between the milkweed stem and the edge of the container with plastic wrap or foil so that the caterpillar(s) don’t fall in the water and drown! Caterpillars don’t need to drink water directly, as they get all the water they need through eating milkweed leaves. Replace the milkweed cuttings if they start to die, dry out, or if your caterpillar has eaten nearly all the leaves. 

(2) Break off a few milkweed leaves, and wrap the cut ends in a wet paper towel. Be sure to keep the paper towel wet, and to provide your growing caterpillars with fresh leaves every day!

When your caterpillar is ready to form its chrysalis, it will start wandering around, looking for a good, secure spot. It’s especially important to be sure it can’t get out of the container you’ve placed it in now – if it does, you may never find it again! Before it forms its chrysalis, the caterpillar will hang upside-down in a J shape. Don’t worry, there’s nothing wrong with it – it’s just getting ready to shed its skin for the last time and transform into a chrysalis. It’s very important to not disturb it while it is in this stage, so if it chose to pupate on the lid of your caterpillar home, wait to open it until it has shed its skin and the chrysalis has hardened before carefully removing the lid.

After about 10-14 days, you’ll notice the chrysalis starting to darken; it will turn a purple-black color, and you’ll be able to see the orange wings of the developing butterfly! At this point, be very careful not to disturb the chrysalis. Soon, the butterfly will emerge, its wings wet and crumpled. The new butterfly must hang upside down for a couple of hours to allow its wings to dry, and if it is disturbed during this time, it might injure itself and never be able to fly properly.

Once the butterfly has completely dried its wings and starts to flap them, it is ready to go! Release it back into the wild near where you found it, and if it hatches out in Sept/Oct, perhaps it’ll make it all the way to Mexico!

Note: Remember, not all caterpillars will survive until adulthood. Some may become sick, some are parasitized by wasps (this is why it’s better to collect small caterpillars than large ones) and some aren’t able to properly form or hatch out of their chrysalis. As long as you’ve provided your caterpillar(s) with good food, kept them in a naturally lit place, and left them alone while they’re pupating, you’ve done the best you can, and if some of them don’t make it, it’s not your fault! It’s just part of life. Remember, butterflies have different life strategies than us - each female butterfly will lay 100-300 eggs, and only a few of those will actually survive to adulthood.