Answers From the Monarch Butterfly Expert
Spring 2015
News Update | Teaching Suggestions


Dr. Karen Oberhauser plays a leading role in monarch conservation and education. She is a professor at the University of Minnesota, chair of the Monarch Joint Venture, founder of Monarch Lab and Monarchs in the Classroom, and a winner of the White House Champions of Change Award.

Dr. Karen Oberhauser

Q: Do monarchs communicate with each other?

A: They certainly communicate before and during mating, and they may communicate as they are forming roosting clusters during the fall migration and winter breeding – by wing flapping.  But we really don’t know.

Q: If the monarchs are in a habitat, do they leave for another habitat if it's too cold or in bad condition?

A: The adult monarchs can leave, but the larvae and pupae are stuck in a habitat even if it’s too cold or otherwise has bad conditions. Another factor that would affect whether monarchs stay in a low quality habitat is the availability of better habitat.

Q: Do these butterflies communicate, especially with each other during migrations?

A: They certainly communicate before and during mating, and they may communicate as they are forming roosting clusters during the fall migration and winter breeding – by wing flapping.  But we really don’t know.

Q: Recently in the news, I have heard that the Monarch butterfly is being considered to be put on the endangered species list. Although this would be a great thing for the species in general, I'm concerned that if they are put on the list, people like me won't be able to raise the caterpillars, because it is illegal to harbor an endangered species.

A: The details of the rules for any species that is listed as threatened or endangered are determined by the US Fish and Wildlife Service. If monarchs are listed, there will probably be a provision for people who rear small numbers from their yards.  The original petition mentioned a limit of 10, but there are new suggestions for 100. In any case, people who rear monarchs for a citizen science program would probably be allowed to rear more under a permit issued to the organizer of the citizen science program – this would also have the benefit of helping us to learn more about monarchs. I would suggest that you read about the Monarch Larva Monitoring Project, and report the outcomes of your rearing to this project.

Q: Do all the monarchs  at a particular geographic location determine at about  the same time that it is time to migrate south or the time to move is determined individually?

A: All monarchs in the same geographic location are exposed to the same environmental cues that trigger migration. However, there is probably some underlying genetic variation in their responses to these cues. Also, individual may vary in their age or condition, which could affect their responses.

Q:  For whatever mechanism they use to determine the time to migrate south,  do they  start the journey as soon as they determine it is time or is there some kind of preparations they have to go through after they have determined it is time to migrate?  That is, is there a stage between the time they determine  it is time to migrate and the time they actually migrate?

A: We really don’t know the answer to this question.

Q: In any geographic area (for example in an area as large as southern Ontario, or an area of just a few hectares), typically, what is the time between when the “first” monarch  and the “last” monarch begins their journey south?  I am not looking for an exact answer for this specific question, just a rough idea.

A: We know that monarchs start leaving northern locations (say Minnesota or southern Ontario) as early as mid-August, and some are still leaving in late September. This gap is usually due to the variation in developmental stage; in mid-August, there are still some eggs and larvae present, and they won’t be adults until late September.

Q: Are the best nectaring flowers/bushes for monarchs that are suitable for Duluth, MN gardens? Can you name varieties that bloom as the summer progresses to fall?

A: Good spring plants are dandelions, lilacs, and even some tree flowers. In the summer, there are lots – milkweed, black eyed Susans, Culver’s root, coneflowers, and many others.  Fall species include blazing stars, ironweed, any aster, and goldenrods.

Q: Is it likely that monarchs would be able to take advantage of an elevated garden, 7 stories high? I want to help out monarchs by planting milkweed this spring. However, I live in New York City and my only outdoor access is a roof garden.

A: That is an excellent question; I don’t know!  I would plant some milkweed and nectar plants and see what happens.

Q: Are milkweed/wildflower plantings along major highways really a good idea? Wouldn't it be better to locate plantings along rural field edges away from automobile corridors?
In Texas one autumn day, I saw probably thousands of migrating monarchs getting hit by cars along I-35 between Austin and San Antonio, likely because roadside plantings were attracting them.

A: Yes, it probably would be better to locate planting along rural field edges or rural roads. Monarchs do get hit by cars, but we really don’t know if locating the milkweed along the roads would lead to a lot of mortality, or if any mortality that did happen would offset the value of the planting to monarchs.  You saw migrating monarchs, and these individuals fly a lot differently than summer monarchs. I guess the important question is, can we afford to not plant milkweed in any areas that are available to us? We have a lot of lost habitat to make up.

Q: Much of the milkweed where I live is plagued by scores of earwigs that wait in the top center leaves for the caterpillars. None survive where there are earwigs. Is there anything I can do to prevent these infestations?

A: Not really.  You could try picking them off, but it’s my experience that their populations fluctuate a lot from year to year, so hopefully you won’t have as many next summer.

Q: I would like to start some Swamp Milkweed seeds and put them into existing gardens in the Detroit area of Michigan. Do you have any tips for how to grow from seed, and when Monarchs will need them to be in bloom for that region? Also, which are the best host plants for caterpillars?

A: There is great information in this guide from the Xerces Society on growing milkweed:
You really don’t need to worry about blooming time, since monarch larvae use milkweed plants with and without blooms, and the adults will be around when they bloom (but the adults will need other sources of nectar when the milkweed isn’t blooming, so be sure to include other flowering plants in your gardens). Swamp milkweed is a good source of food for the larvae, as are other species.  The Milkweed Fact Sheet from the Monarch Joint Venture has a list of species that are great for any region in the US:

Q:  I live north of Chicago and have planted many milkweed plants. What are some good plants for the adult monarch who will make the trip back to Mexico? I have some butterfly weed but that will not flower in the fall during migration. Thank you

A: Good fall nectar sources in the Midwest include blazing stars, ironweed, any aster, and goldenrods. 

Q: Why are monarchs orange?

A: The most basic answer to that question is that the orange scales on their wings absorb other colors, and reflect back orange light, just like anything else that’s orange.  But probably the reason that they’ve evolved to be orange is that bright colors serve as signals to other animals that monarchs are not good to eat. This is called aposematic, or warning, coloration.

Q: Do the monarchs just die if they're hit by a hailstone?

A: Generally, monarchs don’t fly when it’s raining or hailing, so they wouldn’t be too likely to be hit by a hailstone. However, if a large enough one hit them while they were sitting in a tree, or if they were a larva or pupa on a plant, I imagine that they’d die.

Q: If I were to buy monarch butterfly caterpillars and release them on my milkweed, would the butterflies of these animals be pre-programmed to migrate? Or is that instinct only bred into certain monarchs?

A: For reasons outlined at this link, we do not recommend buying monarch caterpillars from commercial sources. See "Raising Monarchs Safely" (go to the link Raise Safely)

Q:  I visited Cerro Pelon and El Rosario sanctuaries and watched a handful of monarchs flapping their wings very rapidly. Both days were overcast with occasional light drizzling. Few monarchs were venturing off the roosts, so I'm guessing the rapid wing flapping was to keep from getting too cold and dropping to the ground. Would that be correct?

A: There are different theories about the rapid wing flapping, and the truth is that we don’t really know.  They could have been warming up. I’ve also been interested in some research in other organisms on mitochondria during long periods of inactivity. The mitochondria in the cells change a fair amount, and it’s possible that monarchs fly during the winter to keep their mitochondria active, and thus ready to support flight when it’s time to remigrate.  This is a really great question that I’ve often wondered about! 

Q. Has there been an experiment that moves western monarchs east of the Rockies? I am curious to know that if this was done, would a western monarch migrate to Mexico or head back west to winter at the California winter sites. Same question concerning taking eastern monarchs and releasing them on the west coast.

A: There were transfer experiments conducted several decades ago in which monarchs from the east were moved to west of the Rocky Mountains. Some of these did end up in the CA wintering sites. Transfer of monarchs between populations is no longer allowed to avoid disease transfer or other problems.

Q: I saw about 15-20 Monarchs in Half Moon Bay 2 weeks ago. They were in a field near Eucalyptus and Cypress trees.  Could they be wintering here in these trees?

A: Yes, I have seen reports of wintering monarchs in this area.

Q: I raise monarchs that lay their eggs on the milkweed I have planted in my backyard. There is a field not a block from my house that has many milkweed plants that I check regularly but they have nowhere near the amount of eggs that are on my plants. My question is do the butterflies from previous years that I have released have the ability to return to where they were born like a hummingbird that returns to my feeders from previous years. I guess I am wondering if my location is implanted for future generations.

A: We usually find that densities of monarchs are higher on garden milkweed than in more natural areas. This could be because the milkweed in your yard is in better condition, or that there are just so many milkweed plants in the field near your house that the number of monarchs per plant is much lower. There is no evidence that information on a good habitat is implanted for future generations.

Q: When will the first monarchs arrive in northern Ohio this year?

A: According to data collected by Monarch Larva Monitoring Project volunteers, there are usually monarch eggs in Ohio by late May or early June.  You should also watch the Journey North maps!

Q: I have been raising and releasing butterflies for some years. I thought birds did not eat them until I saw the predation taking place in my yard by sparrows. I have heard that milkweed loses some of its potency as you go further north. Is this true? Wasps also seem to take a toll.

A: There are bird species that eat monarchs, but I’ve never heard of sparrows eating them.  It could be that you had a naïve bird who didn’t know that they taste bad. But you’re right that wasps eat them.

Q: Is the kind of milkweed that the seeds have to be in the six weeks of winter the bad one or is it okay and we keep the seeds it the fridge should we start planting early this year

A: Tropical milkweed does not need to be cold-stratified, so if you live somewhere in the north, seeds that you do need to cold-stratify are more likely to be native. The timing of planting will vary with where you live, but you can start milkweed seeds inside anytime.  You can also sow them outside in the fall, and they’ll cold-stratify themselves.  For more information on milkweed species that are appropriate for any region in the US, see the Milkweed Information Sheet on the Monarch Joint Venture website.

Q: What is the most embarrassing mistake you have ever made that you are willing to discuss?

A: If you mean a monarch-related mistake, when I was a graduate student, I once left a plastic container of monarch larvae on my deck in the shade, but the sun moved until they were in the sun, and they all died. I felt terrible; this is really more sad than embarrassing, but I’ve never done that again.

Q: Where do the monarchs that overwinter in Mexico come from? Do these monarchs actually migrate? From where. And how long do these monarchs live?

A: The monarchs that winter in Mexico come from a large region depicted on the map on this page on the Monarch Joint Venture website: These monarchs can live up to 8 or 9 months as adults, vs the approximately 1 month lifespan for the non-migratory summer individuals.

Q: Is there more than one kind of monarch?

A: Danaus plexippus is a single species; this is what we mean when we say monarch. There are other species in the genus Danaus, and these species also eat milkweed. They are often called the milkweed butterflies.

Q: My family and I raise monarchs. Is there anything we can do to help.

A: The best thing you can do for monarchs is to make sure that they have habitat available when they come to your area. You can also teach other people about how they can help monarchs, and you can donate money to organizations that are working to protect monarchs and their habitat.

Q.: I am a high school student researching tropical milkweed/monarchs in the Florida Panhandle, and an extremely unusual occurence of three waves of monarchs came through this year in Mid-August, Early October and Mid-November. I have never seen this before. Can you theorize why this occured?

A: I would guess that the monarchs coming through in August and October were coming from north of you, and represent early and later phases of the migration. Sometimes the August movement is called the pre-migration migration in the central US, and usually consists of reproductive individuals that were probably laying eggs. The October butterflies were probably a combination of the offspring from the August flight, and others that were migrating through on their way to Mexico. It’s possible that the mid-November ones were another generation produced locally.

Q: During the three waves of Monarchs passing through Northwest Florida, I counted around 400 eggs total, all of which were predated in August or predated/destroyed due to freezing temperatures during the other two events. Fire ant predation seemed to be a factor, but can you tell me if predation is known to be less on the indigenous milkweed, or if other factors exist due to the type of milkweed in my study?

A: There is not good evidence of differences in predation rates on different species of milkweed, but it sounds like you might have a good set-up to test this!

Q: I plan to continue my study in this area, including tropical vs. native milkweed ecology. Do you have any wisdom or advise for setting up this study? I have concluded that Asclepias curassavica is encouraging predation or extirpation of the monarch population along the southern route of the migration - do you agree with this conclusion? Why or why not? I know these questions are extensive, but I would love to discover why the monarch population is decreasing. I am attending the State Science Fair in April with my current project and would love to share it with you.

A: I don’t know of evidence that A. curassavica increases predation rates.  I do look forward to hearing the final results of your study!

Q: Are there certain plants the monarchs choose to rest on during migration?
I once saw a cloud of monarchs land on one of our trees--not sure what type of tree it is--during migration.  They stayed there about an hour & moved on.  I have been wondering what attracted them to that particular tree.

A: They will roost on many species of tree.  It is probably the location of the tree more than specific characteristics of it.  Andy Davis, Nate Nibbelink, and Elizabeth Howard did an interesting study of characteristics of fall roost sites using Journey North data.  You can access the paper at Andy’s website – click here, go to the Publications page, and look for this paper: Davis, A.K., N.P. Nibbelink and E. Howard. 2012. Identifying large- and small-scale characteristics of migratory stopover sites of monarch butterflies with citizen-science observations. International Journal of Zoology, Article ID 149026

Q:  Would Monarch Butterflies thrive in S.E. Alaska? I love Butterflies and we just do not have very many butterflies here in Ketchikan, AK. Would Monarchs thrive here?

A. Because monarchs would need to migrate so far from their winter sites along the CA coast, through a lot of difficult habitat, it is unlikely that you’d ever see them in southern AK.  But there are some other cool butterflies there that don’t need to migrate, so I recommend doing what you can to provide habitat for these butterflies.

Q: Can you provide a sense of proportion of the threats to monarchs during migration, from most lethal to incidental? I understand that their biggest problems are deforestation, habitat loss (especially because of industrial farming with GMO plantings), and climate change. Is logging in Mexico coming under control? We are doing an interactive drama in which most participants will "die" of various causes, and I want it to be accurate. A few will get through and will be warmly welcomed to Lowell, Massachusetts!

A: While it’s difficult to attribute exact proportions to different threats, my opinion is that habitat loss in the breeding area, habitat loss during the migration, and habitat loss in Mexico at the wintering sites are most important, in that order.  Other factors include climate change, insecticide use, and increasing disease incidence. The Mexican government has been very effective at decreasing the amount of logging in the winter sites.

Q: Is there anyone specifically working on connecting citizen groups who are trying to provide unbroken habitat on monarch flyways? I am interested in E.O. Wilson's "Half-earth" concept, and would love for my teen group to network with other youth and/or gardening groups to make sure the butterflies get to Massachusetts, where, we hope, lots of milkweed will be waiting!

A: If you visit the Monarch Joint Venture website, there is a page called Success Stories where people can enter information about their monarch habitats. This is one way to connect with other groups who are creating habitat.

Q: I'm growing milkweed in my yard in Naples, FL. I've been moving caterpillars to a plant inside a mesh container to protect them from predators, where they eventually crawl to the top and pupate, and I release them when they emerge. Lately they are crawling to the top, starting to pupate, but the process stops with only a little shell exposed, and they die, hanging there. Question: Are they being damaged by handling (moving them from one plant to another)? Or did I have too many in the container, and they tried to pupate before their time? Please help.

A: This happens sometimes, and is often a sign that the larvae are weak for some reason, and can’t pupate properly. If you have been rearing them in the same mesh container without sterilizing it in between, you may be building up OE spores in the container, which could weaken them.  There is a fact sheet with tips for rearing monarchs successfully on the Monarch Joint Venture website:  click here and scroll down to rearing monarchs responsibly.

Q: At the Journey North Monarch site, a photo shows people holding tags that they collected and the tags are not attached to Monarchs. Do the collectors only take tags from dead Monarchs that they find? Or, do they also catch live Monarchs and remove the tags and let the Monarchs fly free?

A: It is my understanding that most of the tags are collected from dead monarchs.

Q: For the past several years, I have tagged 200 Monarchs each fall in my yard on Maryland's Eastern Shore. I have searched the internet looking for statistics on where tags recovered in Mexico originated but I have had no luck in finding anything. My search skills may be lacking.

A: Try this website link:

Q: Is there a way to tell a male caterpillar from a female caterpillar? I know you can tell on a chrysalis but I don't know about caterpillars.

A: You can tell them apart, but you need to dissect (and thus kill) them.  The male testes are readily visible by the 3rd instar.

Q:  Would it be possible to establish a monarch habitat in Seattle, WA?  Our son has a farm there and is interested.

A: Seattle is not a center of monarch activity, but there are some records of small patches of milkweed south of the city, so monarchs might find them every once in a while.  I would recommend that your son focus on some of the cool species or butterflies, moths, and bees that are more common to the area.

Q: I saw Milkweed seeds for sale. They re not treated, but should I be cautious about planting seeds that may not be from my state?

A: Ideally, it is best to plant milkweeds, and other native plants, that are as locally-sourced as possible.

Q: I'd like to know if mice, or other critters would eat the monarchs that have fallen to the ground in the sanctuaries.

A: Yes, there are mice in the winter colonies that eat monarchs from the ground or from low on tree trunks.

Q: Is it unusual for monarchs to be in Arizona during the winter?

A: I asked my colleague, Gail Morris, to help with this question.  Gail lives in Arizona, so is very familiar with monarchs there. She said that monarchs are common in small numbers in the deserts in AZ during the winter unless there is a hard freeze. They can be seen visiting flowers in garens on warm sunny days.

Q: With winter still having a big hold on most of the U.S. will monarchs sense this and stay in the southern U.S.?

A: They don’t come north until it’s warm enough. But late freezes or cold snaps can be a problem for them after they’ve moved north.

Q: I’m wondering about the tags collected in Mexico. Do the tags fall off over the winter or are they collected from dead monarchs?

A: It’s my understanding that most of them are collected from dead monarchs, but some are seen on the wings of living monarchs. Few fall off.

Q: I don't understand how the tag system works. Are they somehow attached to the monarch or what, please?

A: They are stickers that are stuck to the monarchs’ hind wings.  You can read about them more on the Monarch Watch website.