Monarch Rearing

Rearing monarchs

Should I buy monarchs to release in my garden?

We DO NOT recommend purchasing monarchs from commercial butterfly growers to release into the wild. While some breeders may be cautious of disease and test for parasites, many monarch researchers believe that the practice of mass-rearing and selling of monarchs is unlikely to benefit the population, and could actually hurt it. For more information about these concerns, visit Journey North’s Raise and Release Safely page.

How much milkweed does it take to feed one caterpillar?

We generally estimate that it takes about one fairly mature milkweed plant to feed a monarch caterpillar. The early instar caterpillars eat very little, but a 5th instar could eat 4-5 large common milkweed leaves. This of course depends on the species of milkweed that the caterpillar is feeding on because some species have much narrower leaves.

How do I clean or sterilize my rearing containers?

Clean your rearing containers often with a 20% bleach solution. Ideally, soak containers in the bleach solution for ~20 minutes and then rinse thoroughly. This should be done each time a new monarch is introduced to the container, or whenever you suspect signs of disease.

Clean or remove frass (caterpillar poop) from the container daily and make sure that the milkweed in the container is always fresh. Do not leave milkweed leaves in the container long enough for them to get moldy.

Can I keep adult butterflies with caterpillars?

No! Adult monarchs can spread OE parasite spores to monarch larvae if they are infected, so it is best to be cautious and never keep adult monarchs in the same cages as your growing larvae.

What makes a good rearing container?

Monarchs can be raised in a variety of different containers. Mason jars, clear plastic containers, aquariums, plastic shoebox tubs, and wooden/mesh cages can all be good rearing containers. Just make sure that they are somewhat transparent and have adequate ventilation for the monarch(s) to breathe. Containers should NEVER be kept in direct sunlight, as this can be very dangerous and often fatal to the monarch inside. For more information about rearing containers, see the rearing page on our website.

How many caterpillars can I rear in one container?

Whenever possible, we recommend that you raise only one monarch per container. This helps to prevent the spread of disease, and allows you to track individual monarchs and report your observations to projects like the MLMP ( However, many people choose to rear multiple monarchs per container. How many monarchs to keep in one container will depend on the size of the container. For example, in a 1 quart deli container, we would recommend raising no more than 3-5 monarchs. In a plastic shoebox container, you could safely raise about 10. In any situation, it is important to avoid raising monarchs of different sizes (instars) together. Keeping larger 4th or 5th instars with eggs or 1st instar larvae could cause the larger caterpillars to eat the eggs or outcompete the smaller caterpillars for food.

What should I do if my monarchs are dying and appear diseased?

There are many things to be cautious of when rearing monarchs, including disease. In general, monarchs in the wild are solitary, meaning that they do not usually come into contact with other monarch caterpillars. This helps to minimize the spread of disease, so when monarchs are raised in close proximity to one another, disease can spread quickly. Signs of disease vary greatly. Some monarchs become pale and lethargic and eat very little, sometimes not at all. Others appear healthy one day and are dead the next day, often turning completely black or brown in color. We’ve also found that an early sign of disease in monarchs is when a caterpillar appears dark (thicker dark stripes on the caterpillar’s body). Any caterpillars with symptoms of disease should be isolated from other monarchs as soon as possible. Do NOT handle any monarchs suspected of being diseased if you are planning to also handle healthy ones. Make sure to properly wash your hands before handling.

Another symptom to watch out for is if caterpillars appear to be vomiting green liquid. This is a typical symptom of poisoining, and chances are the milkweed your caterpillars are feeding on has been treated with pesticide. If it is not too late, find a new source of milkweed to feed them!

When is a good time to release a newly emerged adult monarch taking into account weather and the migration?

When monarchs emerge (eclose) from their chrysalis, they will hang with their wings down for several hours as they pump them with fluid from their abdomen and dry off. It is important that they be able to hang like this with plenty of room for their wings to be straight. If the wings do not dry properly the monarch may not be able to fly.

Once the wings are dry the monarch is able to fly – if the monarch is beginning to fly around in its enclosure you are safe to handle it carefully and gently to release it. We usually tell people to wait about 4-5 hours after the adult emerges before touching it.

People often ask us what to do if the weather is bad and when it’s safe to release monarchs or how late is too late for them to join the migration. Here are some general tips:

1. Monarchs cannot fly unless their flight muscles are about 55 degrees F. If the weather is cool, cloudy and either very windy or rainy, it’s best to wait for a warmer or sunnier day. If it’s cooler and sunny, releasing monarchs should be fine as they will absorb as much heat from the sun as they can.

2. These temperature and weather concerns are usually only a concern as the migration nears and the weather begins to change near the end of summer (particularly in the Midwest).

3. If you’re wondering when the migration in your area will be starting, look at the maps on the Journey North website for monarch migration, and see what the Monarch Watch website says on estimated peak migration this year. Keep in mind these won’t be exact but they’ll give you a general idea.

4. If you have late monarchs (monarchs that have eclosed past the time when most monarchs have already left your area) and you still are looking to release them, wait for a string of warmer days if you can. The monarch has a better chance of making it to Mexico if you release it than if you do not.

5. If you do need to hold on to an adult for a day or so because conditions are not ideal for release, you may need to feed it. Cut flowers are best if you have them, but a solution of honey or sugar and water will also work. Just mix up 20% honey or sugar with water and soak a cotton ball or clean sponge in it. The monarch may not recognize this as food, but they can learn! If they don’t find the food on their own, just gently hold them between two fingers (making sure all 4 wings are secured between them) and place them so their feet touch the cotton ball with the mixture. Sometimes this is enough to get their proboscis to uncurl and begin feeding. If it does not uncurl, you may need to gently take a toothpick and uncurl the proboscis until it touches the food. Then the monarch will know this is food and hopefully begin to drink. If it does not drink it’s probably not hungry yet. When it curls it’s proboscis back up and begins to move away from the food you’ll know it’s done. After learning that the cotton ball contains food you shouldn’t have to feed them by hand again. Food should be offered every day, but they may not eat.

Is there a way to tell when a chrysalis is about to open?

Sort of! The very last thing to form in this stage is the pigment, which is what you see when the chrysalis “turns dark” as some people say. It’s not really “going clear” – the pupa casing has always been clear, but the organism underneath is changing colors.

Once you can see the black and orange pigments of the adult’s wings beneath the pupa casing, you’ll likely have an adult within the next 24 hours.

Beyond that there are no other tells that a monarch is ready to emerge from the chrysalis. You’ll just have to watch it carefully. If you do see it start to crack open, you’ll know emergence is immenent. Definitley stick around to watch! Look away and you might miss it!

Does rearing late summer monarchs indoors affect whether or not they will be able to migrate to Mexico?

Great question – it would be best to try to mimic outdoor conditions as much as possible. We don’t really know exactly what combination of environmental cues triggers reproductive diapause, and when that response is triggered during development. We do know the cues that trigger it, but can’t say for sure when those cues are most important for inducing diapause.

That said, yes, keeping them indoors where temperatures don’t fluctuate and they may experience different night/day regimes from artificial light could potentially impact their ability to go into diapause (prepare for migrating). If you keep them indoors, it is probably better to keep them in ambient light/dark cycles.

Our work on temperature (Goehring and Oberhauser) showed that it temperature does have an effect although the effect of daylength is stronger.  A large day/night difference is more likely to induce diapause.  Temp, milkweed quality, and daylength seem to have additive effects.

What do I do if I run out of milkweed while rearing my caterpillars?

Monarch caterpillars eat a LOT and people are often surprised by how much food one caterpillar can go through in a day. If you do end up running out of milkweed – don’t despair! While it’s best to have a constant food source available, research has shown that a caterpillar can go 24 hours or so without food and not be negatively affected. This does not mean that you should only feed them every other day – they still need food every day for the best chances of survival.

If you’ve been collecting from your yard, you’ll have to go elsewhere for the milkweed. Check local public places, but be sure it’s okay to take plants from there! Sometimes you’ll find milkweed along walking paths or public roads, particularly in suburban or semi-rural areas. In Minnesota you cannot take plants from State Forests without a permit (excepting fruits and mushrooms). Check the rules on taking plants with your local DNR or county government.

Once you find a source for milkweed, you’ll want to rinse it thoroughly before feeding it to your larvae. This will increase the chances that it’s not covered in pesticides or other harmful chemicals.

See the Monarch Joint Venture fact sheet.