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Frequently Asked Questions


What do I do if one of my monarchs is infected with OE spores? Should I still release it?

Please visit Project Monarch Health for information on Ophryocystis elektroscirrha (OE) infections and how to monitor for this parasite. Since OE spores are not visible to the naked eye, diagnosis of OE requires a microscope or awaiting results back from Project Monarch Health. And since OE is a naturally occurring parasite, it is recommended that all monarchs be released if they appear healthy, as long as your rearing operation follows the best practices for minimizing the spread of disease. In cases where monarchs likely have OE and emerge with crumpled wings and deformed body parts, we do not recommend releasing them. Butterflies that cannot fly on their own should not be kept in rearing containers as they are likely spreading OE spores throughout the container or environment, and will likely increase the spread of the parasite to other monarchs you are currently rearing or that you rear in the future. Euthanizing heavily infected and deformed adults is recommended to minimize disease transfer to your containers or other monarchs. Thoroughly sanitizing rearing containers between each monarch, and preventing adults and larvae from occupying a shared container will help prevent disease spread. You may euthanize your monarch humanely by placing it in the freezer.


Can I report the monarchs I rear to other community/citizen science projects?

You can also test the monarch for OE and report it to Monarch Health, and tag it during migration season for Monarch Watch (east of the Rocky Mountains), or Southwest Monarch Study (west of the Rocky Mountains). For a complete list of monarch community science/citizen science programs, please visit:


How do I prevent the spread of disease between monarchs I’m raising?

Thoroughly sanitizing rearing containers between each monarch, and keeping individuals in separate containers will help prevent disease spread. Make sure to clean out the frass from each larva’s container every day.

To sanitize your rearing containers, follow these steps:

  • Wash all the rearing materials and containers with dish soap and water.
  • Soak the containers in a water-bleach solution of 10% strength (1 part bleach to 9 parts water). Let the containers sit in the solution for at least 20 minutes. For mesh cages, pour the bleach solution in a spray bottle and coat the cage in the solution.
  • After letting the solution sit for 20 minutes, wash off the containers and other rearing materials.

Where can I buy monarchs to raise?

We highly discourage purchasing monarchs from commercial retailers to raise and release into the wild. Monarchs bred in captivity for commercial purposes have a lower genetic diversity, higher disease transmission rates, and are less genetically and physically fit compared to their wild counterparts. Head here for more information.


Can I keep adult butterflies once they have emerged?

If you rear your monarchs responsibly, it is best to release them 24 hrs after they eclose so they can live with the wild population. We do not recommend keeping them or using them for captive breeding purposes. If you are not releasing them because it is too late in the season and they have missed their migratory window, you may choose to care for them until they pass or euthanize them humanely by placing it in the freezer.


Do overcrowding issues occur in the wild?

There could be increased risk of disease transmission if there are high densities of monarchs in the wild. In small patches, or on certain kinds of milkweed, this could also lead to a food shortage. Enclosed spaces (such as mesh tents) have an increased risk of disease transmission and cannibalization in comparison to outdoor spaces.


Are there concerns about rearing in mesh tents that are kept outside?

Rearing monarchs outside has been found to be the best way to rear. This method will have the least effect on their migratory ability, as they are still exposed to sunlight and natural conditions.

However, even large mesh rearing tents can pose potential risks for monarchs. The tents could facilitate the spread of disease among the monarchs by keeping them closer together than they would naturally be able to distribute themselves. The tents may also keep out insects that are beneficial, and trap whatever is in that area inside the enclosure (including parasitoids, insect predators, etc). 


What kind of container(s) do I need to raise monarchs?

Plastic or glass containers/cages are preferred because they are easy to disinfect. Wood is difficult to disinfect and should be avoided. Pop-up or net-style tents can also work, but make sure to clean and sanitize them to prevent the spread of diseases. Note that keeping adult butterflies in these types of tents for extended periods of time will damage their wings.

Monarchs should be reared individually in separate containers to prevent disease transmission and for ease in monitoring/reporting to community science programs. Label each container with information about the monarch collected including the date, stage at collection, location in which it was found, and a unique identification number/code.

Here are some suggestions:

  • Food storage containers with small holes punched in the lid
  • Glass jar with a mesh lid, feel free to put a stick in the container to help them climb
  • Mesh pop-up tent

Should I only collect certain stages of larvae?

If you collect 4th and 5th instars for MLMP, you will not affect your observations for subsequent weeks, since these monarchs would pupate in the next week. If you collect eggs or younger larvae, you should note this on the site information page so that analysis of your data takes collecting into account.


I ran out of milkweed and cannot get any more. What should I do?

Monarchs are obligate feeders of milkweed, so milkweed plants are their host and they depend on them as their sole food source when they are larvae. If you plan on raising monarchs, it is very important to ensure that you will have enough milkweed for them before you rear them out. If you are not sure if you have enough milkweed, do not raise them. As a last resort, monarchs have been observed eating squash like pumpkin or butternut (organic) in their later instars as a temporary food source until more milkweed has been obtained. This is not a sustainable food source for them. If they are in their last instar, this could be enough to get them to the pupation stage, but squash lacks some properties of milkweed that the larva need. Milkweed produces cardiac glycosides, which the larva is able to sequester as they consume the plant and utilize it for their benefit. This compound protects monarchs by making them toxic and distasteful to predators.


My monarch stopped eating and hasn’t moved in a few hours. Is it dead?

Larvae stop moving and eating for 7-24 hours prior to molting (dependent on humidity, temperature). If it is warmer and more humid, they will molt faster than when it is dry and cool. They may leave the milkweed plant to molt on the lid or side of your container. Do not move it, as it is fragile during this stage. It will continue eating when it is ready. Read more about the molting process here.

If it doesn’t resume normal activity after about a day and has not molted, there may be another underlying issue, like disease.


Is there any indication that feeding caterpillars leaves that have been cut compromise the health or growth of the caterpillar rather than the caterpillars eating fresh milkweed that is growing?

No, either is fine!


How do I feed adult monarchs?

Adult monarchs (butterfly life stage) require sugar to survive. In the wild, they consume flower nectar as their food source. A monarch should be released 24 hours after eclosion (handling before this risks damage to its exoskeleton before it completely hardens). If weather (storm or rain) prevents release at this time, you should feed it. It can be fed 20% concentration honey/water solution, fresh fruit (such as cut up melon), or fruit juice on a clean sponge in a shallow dish. To prevent fermentation, these should be changed every day. The sponge and dish should be sanitized with the rest of your rearing containers. You can also put flowers in their enclosure for them, but be sure that they are flowers they like to nectar from and are also changed regularly.


Do you have best practice suggestions for rearing monarchs?

Head to these pages to learn more about how to rear monarchs: Rearing, and Rearing How To's for Activity #3.


Where is the middle ground then, in being able to contribute to the science and data (inside rearing), vs outside, where it's more natural habitat and rearing doesn't negatively impact their natural triggers and migration?

Generally, raise just a few every summer, and no more than you can easily take good care of. Raise them only for educational purposes or to contribute to citizen science. And if you are worried, don't raise monarchs from the final generation that should migrate (so they can get their natural cues to do so). If you can do it safely (without baking them in the sun) raise them outdoors. Otherwise, if indoors they should be exposed to natural light.


Does bringing monarch larvae inside and letting them grow inside (as instar and/or pupae) impact their migration?

There is growing evidence that rearing monarchs inside, where they are not exposed to all of the environmental cues that they would have outside, can affect their propensity and ability to migrate


What is considered mass rearing?

There is not a commonly accepted threshold for mass rearing operations. The term often applies to commercial breeding operations, but could also extend to groups or individuals who strive to raise hundreds or thousands of monarchs each year.


How do I raise monarchs?

Reference our rearing page for a guide on how to rear monarchs responsibly.


Should I rear monarchs or not?

This is an issue that really depends on your personal feelings about individual monarchs. There are strong opinions on either sidefor you to consider, and a good starting place is our Rearing: Why or Why Not? page and this Monarch Joint Venture webinar on the topic.

  • Pro rearing: you will, in all likelihood, save the individual monarch’s life. Only about 2-5% of wild monarchs survive from hatching to adulthood. You will learn about and become more connected to monarchs. If you report what happens through our Activity #3, you will help us learn more about monarch survival and natural predators. And, if you are collecting and rearing eggs from an MLMP site, you can tell us you are doing that in the site information section, and we will take that into account when we analyze your data. We won’t use your data in survival analyses, because you are affecting survival.
  • Con rearing: there is good evidence that rearing inside affects monarch behavior (you’ll learn about that in the webinar). You might have the impression that you are helping the monarch population by saving some individuals, but you really aren’t—one, ten or even a hundred monarchs won’t make a difference. If you want to save monarchs, create habitat! Even if we do rear enough to be more than a drop in the bucket, without habitat out there for them, it won’t really matter.

Where is it required to obtain a permit or authorization to handle monarchs?

California is the only US state that requires a collecting permit for invertebrates. This includes any type of collection such as using them for scientific research or teaching, or collecting them to rear and release. More information on the California permit can be found here. Monarch Alert provides a blanket permit for their volunteers in California. Information on how to participate in CA tagging efforts can be found here.

In Mexico, it is illegal to touch monarchs, and in Ontario, Canada a permit is required to rear and handle invertebrates (including monarchs). In Nova Scotia, Canada, Monarchs have been listed as endangered, so they and their habitat cannot be touched without a permit.

There may be rules and regulations that we are not aware of that apply in additional states and provinces.

Monarch Biology

How do wasps parasitoids use monarchs as hosts?

Less is known about the extent to which other parasitoids attach monarchs, but at least one wasp in the family Braconidae has been reported in monarchs (Arnaud 1978). The closely-related queen, Danaus gilippus is parasitized by two Chalcid wasps as well as L. archippivora (Arnaud 1978). Current research in the Monarch Lab demonstrates that the wasp Pteromalus puparum (in the family Pteromalidae and the same superfamily, Chalcidoidea, as the two Chalcid wasps found in queens) could be an important pupal parasitoid (Oberhauser et al. in preparation). Pteromalus puparum wasps are tiny, and over 200 can emerge from one monarch pupa.

Monarch Biology

How do tachinid flies develop within monarch larvae?

Female La (Lespesia archippivora) lay eggs on the host integument (skin), and the fly larvae hatch and bore into the host soon after oviposition. La complete their larval development within the host, the maggots emerge from late larvae or pupae, and then pupate in leaf litter and eclose within about 10-14 days. Fly maggots drop to the ground on long, gelatinous tendrils that look like white strings hanging from the monarch.

Monarch Biology

Are there parasitoids that use monarch larvae as hosts?

Both fly and wasp parasitoids use monarch larvae as hosts, but the most important larval parasitoid is probably a fly species in the family Tachinidae. This family includes about 10,000 species, most of which parasitize Lepidoptera (butterflies and moths), although they also parasitize Hymenoptera (ants and bees), Heteroptera (true bugs and their relatives), Coleoptera (beetles), Diptera (flies and mosquitoes), Dermaptera (earwigs), Orthoptera (grasshoppers and crickets), Chilopoda (centipedes), as well as some scorpions and spiders. Research in the Monarch Lab suggests that species Lespesia archippivora (La) is the most important monarch tachinid parasitoid. It is widespread throughout North and Central America, has been found in Brazil, and was purposely introduced into Hawaii for biocontrol in 1898.

Monarch Biology

Do the same monarchs that migrate to Mexico each fall return to my area each spring? How long does a monarch live, and how far can they fly in a day?

If you live in the northern part of the country, the same monarchs that leave in the fall, on their way to Mexico, don't return to your area in the spring. Monarchs that migrate to Mexico live about 8-9 months as adults (from late summer or fall until the following spring). When these monarchs return to the southern US in March, they lay eggs there and die. The offspring of the migrating monarchs are the ones you see in the mid-section and northern part of the country in the spring. Monarchs that you see in your area during the summer breeding season live about 4-6 weeks. The ones that migrate live longer because a) they don't reproduce until spring and reproduction uses up a lot of energy and other resources, and b) they are in a semi-dormant state while they are overwintering in Mexico. They can fly about 50 miles a day while they're migrating.

Monarch Biology

Is it unusual to find more than one monarch egg on a milkweed plant?

It's not too unusual to find more than one monarch on a milkweed plant. Although an individual female usually lays only one egg per plant, multiple females may use the same milkweed plant.

Monarch Biology

How do you tell which "instar" a larva is in?

If you look on our website in the Biology & Research section, there's a section called Monarch Life Cycle. This shows you comparisons of the head and tentacle sizes for the different instars. The Life Cycle Card set and the Field Guide to Monarch Caterpillars, available in the Monarch Store, also give great descriptions of each stage.

Milkweed Community

I read that while there are 106 types of milkweed, monarchs only lay their eggs on certain kinds, avoiding types with certain levels of toxicity. I’m worried because the only type of milkweed we have so far is the butterfly weed (Asclepias tuberosa) and it has no milky substance in the plant. What milkweeds do monarchs like?

There are actually very few species of milkweed that monarchs won't eat. Among the ones they will eat, they certainly have preferences. We know that female monarchs will lay their eggs on Asclepias tuberosa, and monarch larvae will eat it. However, we find in the lab that A. tuberosa is not one of their favorite milkweeds to eat. If you monitor a patch of A. tuberosa, you will likely find some eggs and larvae on it, but you may not find as many per plant as you would find on some other species (e.g. common milkweed [A. Syriaca] or swamp milkweed [A. incarnata]).

Milkweed Community

As I am monitoring I find a lot of eggs, but I don't see many larvae. What would most likely be eating the eggs or first instar?

There are lots of things that eat monarchs! Ants, spiders, red velvet spider mites and stink bugs are some we see frequently. Some monarch larvae also die when their mandibles get gummed up by the milkweed latex.

Milkweed Community

I observed a mass of 50-100 caterpillars (not monarchs), about ⅓ inch long and white with black heads. The first stage of the larvae looks slightly furry and light brown. They are skeletonizing the milkweed, eating everything but the veins and ribs. Any idea what these might be?

These are milkweed tussock moth caterpillars. They are gregarious for the first week or so, and then will go their individual ways. They'll soon be furry with big tufts at each end of their body. The female lays an egg mass, and the larvae are synchronized in everything they do, including molting.


We are a nature center outside the state of Minnesota and would like to host a training session for several nature centers in our area. How do we go about doing this, and what are our responsibilities?

Contact us to see if a training session in your region fits into our long-term plans. If it does, we ask that the cooperating nature center take care of all the recruiting and planning, and schedule meals and lodging for the naturalists that attend. Our fees will vary depending on the number of our staff needed, the lenght of the workshop and if travel is required. Our base rate is $100/hr per staff needed, plus mileage or travel costs.


I would like to volunteer to monitor monarch populations in my area. How can I be trained to monitor my own site?

The training methods are described on our website. You could teach yourself by using the directions on the website, or attend a training session given by someone who attended a train-the-trainer session in your area. The dates of these sessions are found in the Training section on our website. You can also watch our online training videos if you are unable to get into an in-person training. If you have any questions, feel free to contact us:


Can I collect the daily temperature and rainfall data from my home or the National Weather Service if it is collected close to my site?

Collecting rainfall and temperature data from your site would be best since rainfall and temperature can be quite "patchy". However, if the weather service station is within a reasonable distance from your site, then using that data would be fine. You should make a note of this on your data sheet.


Activity #4: Comparing Plants Occupied by Monarchs to Random Plants. I found an additional 7 monarch eggs when I filled out the Characteristics of Random Milkweed Plants sheet. Do I transfer this data over to the Characteristics of Milkweed Plants with Monarchs sheet and double count the 7 new monarch eggs, or do I keep the counts separate?

The goal with these two activities is to compare a random sample of plants to plants with monarchs on them. Some of the random plants may have monarch eggs or larvae on them and you should just note the monarchs as invertebrates on the plants. You can also put data for theses plants onto the Characteristics of Milkweed Plants Occupied by Monarchs sheet. However, if you are going to count them in your density count for the week, you need to include the 30 plants that you checked as part of your sample size. You should only do this if your random sample of plants did not cross the transect you took to get monarch density. Thus, you aren't really double-counting them.


How will the data that I collect be used?

Once your data is entered into our database, you will be able to see graphs showing the numbers of monarchs that were found at your site each week that you monitor. Graphs for each year are also posted for all of the other sites that are a part of this project, along with annual graphs for the eastern population. The data you collect will help us answer basic ecological questions about the abundance and distribution of monarchs over time and geographical locations. A more comprehensive list of questions that the data can be used to answer appear in the monitoring section of the website.

Not only will scientists be able to publish scientific papers using the data you collect, but since the graphs are available to the public, many teachers and students can use them in their own classroom investigations!

You can see a list of and read papers that have been published using MLMP data here.


I recently came back from vacation and my site was mowed down. What should I do now that I no longer have milkweed?

You should note that it was mowed in the notes for that site, and then hopefully when the milkweed comes back it will have even younger plants that are more attractive to monarchs. Milkweed typically grows very quickly, so you might even start to see small growths of it coming up above the rest of the plants in your area fairly soon after mowing. If no milkweed comes back within a few weeks, you won't be able to monitor – at least until next year.


There have been no monarchs at our site so far this year. Do you still want my data even though it shows no monarchs?

Yes! We definitely are interested in your data. Even though it is discouraging to find nothing, understanding where there are no monarchs and when is just as important as learning where and when there are monarchs. This is important because we'll learn a lot about monarch distribution and population dynamics.


When should I start and stop monitoring my site?

It's best to monitor every week as soon as the milkweed comes up. It is just as important to document monarch absence as it is to document presence. You will almost always see eggs before you see adults, so you shouldn't wait until you see your first adult to start monitoring. In the fall, you should monitor until all of the monarchs are gone. We recommend going out twice after you've seen your last egg or larva.


How many milkweeds do I need in order to establish a site?

In order to establish a MLMP site, milkweed must be present since monarchs only lay their eggs on milkweed. At a minimum, we recommend that you select a site with at least 12 plants. Of note, scientific studies estimate that it takes approximately 30 milkweed plants to produce one adult monarch due to predation, disease and other pressures on immature (eggs and larvae) monarchs. Therefore, while sites with low milkweed numbers may still foster immature monarchs, sites with more milkweed are more likely to yield observational data.


What is wrong with my monarch?

There are many diseases that affect monarchs, so it is usually impossible to determine with complete certainty which disease caused a monarch’s death. A monarch that looks ill or otherwise abnormal could have been infected with a virus, bacteria, parasite, genetic problem, or fungus.

  • Shriveled up:
    • With silk-like threads coming from body:
      • Tachinid flies (parasitized)
    • Parasitized by wasps
    • Disease
  • Turned Black:
    • Black death (common diseases are Pseudomonas bacteria or Nuclear Polyhedrosis VirusNPV)
  • Larva stopped eating and turned pale:
    • Bacterial infection
    • Molting: The larva may appear a bit less vibrant while they are shedding their old exoskeleton. They are fragile during this stage, so it is best to not touch them until they are done molting.
  • Green “goo” came out of the larva:
    • Ate contaminated milkweed, the pesticides most likely caused it to vomit/expel the milkweed.
    • The monarch larva was squished or injured.
  • Bright green ball at the end of the caterpillar:
    • Anal Prolapse (this is always fatal)
  • Failed to emerge properly:
    • OE (use Project Monarch Health’s OE testing kit)
    • Disease
    • Genetics
    • Unsuccessful parasitism
  • Did not finish creating a chrysalis:
    • Genetics
    • Disease
    • They may die in the middle of their chrysalis formation, or right before they are about to pupate (hang in “J-shape”).
  • Chrysalis had dark spotting on it:
    • OE
    • Disease
    • Bruising from being handled
    • Parasitism
    • If the entire chrysalis has darkening pigment, that likely indicates that the monarch will be eclosing from its chrysalis soon.
  • Chrysalis turned brown or black with holes in it:
    • Parasitized
    • If parasitized by wasps (Pteromalus cassotis, a species of chalcid wasps), there will be small black dots on the chrysalis where the eggs were deposited. About 2-3 weeks after parasitism, the wasp offspring will chew a hole in the pupa and emerge from inside.