Answers From the Monarch Butterfly Expert
Spring 2014
News Update | Teaching Suggestions | Facts

Thanks for your great questions!

There is clearly a lot of concern about the monarch population this year, and I thank you so much for this concern. The Journey North and the Monarch Joint Venture ( websites both list many actions that you can take to help monarchs.

Sincerely, Karen Oberhauser

Dr. Karen Oberhauser


Q: I've heard that the non-native Tropical Milkweed (Asclepias curassavica) may be harmful to monarchs. Is this true?

A: Tropical milkweed (Asclepias curassavica) is not native to the United States or Canada. Because it is attractive and easy to grow, it is often the most widely available milkweed at commercial nurseries. Because tropical milkweed historically occurs in the New World tropics, it is adapted to grow year-round, whereas most native North American milkweed species die back each winter. When tropical milkweed is planted in the coastal southern U.S. and California, these plants continue to flower and produce new leaves throughout the fall and winter, except during rare freeze events. Potential negative effects on monarchs include 1) continuous breeding on the same plants, which can lead to a build-up of Ophryocystis elektroscirrha (OE) infection, and 2) availability of milkweed during a time that it is not naturally available, and so potential consequent impacts on monarch breeding during the fall migration.

Q: What can we do to help stop this deadly corn/soybean – ethanol craze that is driving farmers to plant these Monsanto-profit "chemical – intensive" crops that are wiping out milkweed growth? Even though people like us are growing milkweed on our properties, it's just not enough to help the monarchs all that much.

A: While I agree with the general sense of this question, it's a huge issue that I'm probably not qualified to address. I need to believe that we can help monarchs by promoting habitat restoration and conservation, and at least for the time being, the chemically-intensive crop train seems to have left the station. So we need to move on from here and do our best to find other habitat.

Q: I'm sure you are going to be asked this several time. Have you discovered why the decline in the number of Monarch's overwintering in Mexico?

A: While there are many factors that have negative impacts on monarchs, the most important is loss of habitat. This is occurring in the breeding, migrating, and overwintering ranges. Additionally, the incidence of at least one major disease, OE, is increasing; and changing weather patterns are causing more droughts and winter storms that are harmful to monarchs.

Q: Where can I obtain Milkweed for my garden?

A: The Xerces Society has a great resource for locally-sourced milkweed seeds:

Q: What do you believe is the single most environmental danger that threatens the monarch here in California?

A: Habitat loss.

Q: Since the original reason to tag monarchs was to find their winter roosting sites, why do we continue to tag? We have also learned the distance they fly in one day from a tagged butterfly. Scientists assure us the tag does not hinder their flight but so few tagged butterflies are actually found and since their numbers are dwindling, wouldn't it be best to allow them to use ALL their strength to migrate instead of continuing a possibly unnecessary experiment?

A: Monarch Watch runs the monarch tagging program. It would be good to check their website for details on how they're using the data.

Q: What are the chances that the Monarch colony will recover to maximum numbers of the last decade?

A: The answer to this question depends on human behavior. If we all work together to provide habitat, monarchs will be able to survive. It is unlikely that they'll recover to the maximum numbers of the past, given the amount of habitat that has been lost, but they can recover at least partially.

Q: Can a Monarch colony be started on another continent?

A: There are already monarchs in South America, Europe, and Australia, so the answer is yes.

Q: Is there someone who is educating the contracted ditch mowers throughout our state as they mow off the ditches completely leaving no milkweed?

A: This would be an excellent public advocacy role for you to take on!

Q: Is there a way we can conserve the middle of ditches and even have milkweed plantings there so they are untouched?

A: Yes, but roadside managers need to be educated.

Q: I had the pleasure of raising monarchs in central Florida for 3 years. It was fascinating! Can you explain how the caterpillar changes into the butterfly in its chrysalis? It looks like the caterpillar becomes a liquid blob and over days becomes the butterfly.

A: The developmental process from egg to larva to pupa to adult looks from the outside like four very discrete steps. However, metamorphosis and the development of adult features occur throughout the egg, larva, and pupa stages. Features that are unique to the adult develop in a number of ways and at a variety of times, described briefly below. 1. Many of the features unique to the adult—such as the wings, eyes, internal reproductive organs, and long antennae—are actually present as tiny clusters of cells even in the egg. These cell clusters grow and differentiate throughout the larval stage. During the pupa stage, they rearrange and develop further. 2. In some cases, the cells that will form the adult structure are present in the larva stage, but they don't start developing until the pupa stage. For example, the adult compound eye forms from cells that were behind the larval eyes. 3. Some body parts, especially muscles, degenerate at the end of the larval stage and are replaced by new muscles that allow the new kinds of movements associated with the adult stage. Larvae move very differently than adults, and thus most of their muscles are completely histolyzed (broken down by enzymes) early during the pupa stage. New muscles are formed by muscle stem cells.

Q: I just read the letter from the Grupo de los Cien International, and I have a question. On page 2, where it talks about 25-foot road-strips and medians that could be planted and managed to support the growth of milkweeds, it says "If two monarchs were produced per acre of habitat..." Does this mean that, realistically, experts predict that two monarch butterflies per acre is all you can hope for? Two monarchs that can participate in the multigenerational migration? How many monarchs might actually be produced in one acre of habitat? It sounds like there must be a very high level of loss -- of both larvae and butterflies -- to birds, mantids, and other predators, and to environmental challenges.

A: We don't know how many monarchs an acre of habitat could produce, and it will clearly depend on the density of milkweed in that acre. We do know from Monarch Larva Monitoring Project data and other studies done in my lab that the survival of monarchs from egg to adult is very low, probably less than about 5%, so yes, there is a high level of loss. But remember that female monarchs can lay hundreds of eggs, so only a small number need to survive to keep the population going AS LONG AS THEY HAVE SUFFICIENT HABITAT.

Q: I am Living upstate New York in Sherburne, I was wondering what I could do as far as plantings or landscaping to help the Monarchs recover. I've been through this with helping the Bluebirds reestablish in New York. Thanks for your input.

A: Monarchs' needs are simple. They need milkweed and nectar sources in areas that are not treated with insecticides. So any landscaping you can do that includes these needs will help monarchs.

Q: Do you feel it is safe to visit the sanctuaries in Mexico? My wife and I have always wanted to go but each year we "chicken out" because of the political unrest.

A: In my opinion, it is safe as long as you take normal precautions for traveling. I have never felt afraid in the area.

Q: I live in Toronto, Canada. Have lots of garden space (three acres) /sun/ & tried to plant butterfly bush, milkweek, purple colours/ for three years. Very few Monarchs. Who can I consult to help increase the attraction of my garden? How do I protect the eggs?

A: Unfortunately, monarch numbers have been very low for the past three years, so it's possible that they just haven't found your garden. Having lots of milkweed and nectar plants available will make it more attractive. However, if you are in the middle of the city without other habitat around you, it is less likely that they will be able to find your garden. You can bring monarchs inside to rear them if you want, but it's hard to protect them on the plant. The Monarch Joint Venture has a useful How to Rear monarchs Fact Sheet.

Q: I live in Fargo, ND. I purchased swamp milkweed from my local nursery about 10 years ago. It's spread like crazy but it's easy to control. The Monarch Caterpillars have enjoyed it in my yard over the years but I'm wondering if I should try to get the natural milkweed found out in the rural areas in my state?

A: If the monarchs (and you) like your swamp milkweed, that's great. You could try some common milkweed and see what you (and they) think about it!

Q: Are Monarchs looking for the same type of milkweed on their journeys to/from Mexico? Or, is Milkweed all the same for them?

A: Monarchs recognize many species of milkweed as food. There is some evidence that some species lead to higher survival and faster growth, but these studies have not been conducted under natural, outdoor conditions.

Q: If a monarch which grew up and was released in Philadelphia last September made it to Mexico, would his/her descendants join the monarchs returning north on the east coast, or would they possibly end up taking the route to the Midwest and become Midwest butterflies?

A: As far as we know, monarchs migrating north in the spring have no propensity to return to their parents' natal regions.

Q: What is your opinion about releasing monarchs at weddings or other celebrations?

A: Sonia Altizer, Elizabeth Howard, Lincoln Brower, and I wrote about the problems with releases of mass-reared monarchs. Here are our concerns:

1) Mass-production of monarchs makes it easy to transmit disease. Monarchs did not evolve under conditions in which they developed in large groups, and are susceptible to diseases that can be transmitted among larvae. There are no requirements that breeders follow specific disease-preventing protocols, nor are there outside agencies that routinely test captive stock for diseases. The most common monarch pathogen, Ophyrocystis elektroscirrha (Oe), is the easiest to screen for and keep out, but doing so requires constant vigilance. In the recent past, we have noted that some commercially purchased monarchs were heavily infected with this parasite. There is strong evidence that the dissemination of commercially-bought bumblebees used to pollinate glasshouse tomatoes has helped spread two key pathogens, Crythidia and Nosema, into wild bumble bee populations in North America, and this appears to have driven at least one species extinct in the wild. This is certainly a risk we don't want to take with monarchs.

2) The loss of genetic diversity among wild monarchs is also a concern. We don't know how many parents are contributing to the genetic stock of any given purchase, and it is possible that many of the released monarchs could be related. The release of large numbers of individuals with low genetic diversity could contribute to further declines due to inbreeding depression.

3) Studies in species as different as fruit flies and fish show that animals can adapt to captive conditions in as short as one or two generations. When this happens, researchers see a high frequency of alleles that would be harmful or have reduced survivorship in the wild. The more captive generations, the more extreme this effect. Here is a quote from a review paper on this topic: "In captivity, species adapt genetically to the captive environment and these genetic adaptations are overwhelmingly deleterious when populations are returned to wild environments" (Frankham 2008).

Q: Dr. Brower said the monarchs that overwinter on the oyamel pines in Mexico might be leaving a scent marker for future monarchs to return to the same groves. If the monarchs flourish this summer and many more return to Mexico this coming fall, would they be too crowded on those few groves that were used this past winter? or would the overflow re-colonize the neighboring groves and leave a scent there for the fall 2015 monarchs?

A: That is an interesting theory, but it has not been tested at all, so we really don't know the answer to your very interesting question.

Q: Is there a particular species of milkweed that should be planted in the Central Plains (Nebraska) for Monarchs as their host plant?

A: See the Milkweed Fact Sheet on the Monarch Joint Venture website. The best species in this region of common, swamp, and whorled milkweed. You can also plant butterfly weed, and may have some spider milkweed (Asclepias viridis) that far north.

Q: Do Monarchs have a preference of species of milkweed they lay their eggs on?

A: They will lay eggs on available milkweed. In my experience, the condition of the plant is much more important than the species.

Q: If there is a milkweed preference, does it vary by region? For example, would Monarch's be more likely to lay eggs on Common Milkweed vs. Butterfly Weed (A. tuberosa) or Swamp Milkweed? A: Butterfly weed is generally not as preferred as common and swamp milkweeds. The leaves are quite hirsute (hairy) which may make them less attractive. Q: When monarchs travel overseas, where do they rest?

A: We know that they sometimes rest on oil rigs or ships, but I think that they generally don't fly over large bodies of water unless they are blown off course.

Q: Someone told me that people used to tie notes to a monarch butterfly and they would deliver messages like homing pigeons. Is this true?

A: They'd have to use a really small piece of paper! I've never heard of that.

Q: Do both monarchs and viceroys taste bad to birds or are viceroys imitators?

A: Both taste bad.

Q: Is there any current evidence indicating Bt Corn Pollen as an environmental contaminent?

A: In my opinion, Bt corn pollen is unlikely to have an impact on monarchs because there are no longer monarchs in corn fields. Before the advent of herbicide-tolerant corn and soybeans, milkweed was common in these fields and Bt pollen could have posed a risk, but this is no longer the case.

Q: When the toxicity of Nicotine is calculated to an extreme dilution, do you believe we are witnessing cumulative lifetime effect, multi-generational exposure, or possibly aggregate endocrine disruption?

A: I assume that you mean neonicotinoids. Their mode of action is by blocking neural receptors, so I don't think that they affect endocrines.

Q: We own/manage a 170 acre "environmental" in east central Wisconsin. We have been supporting monarchs for many years. Many monarchs use the red sweet clover during their stay. Should I plant more?

A: Red sweet clover is fairly invasive in native fields, so I suggest that you focus on native species which will provide benefits for a wide variety of pollinators and herbivores.

Q: Do you have any information on the Milkweed Bug? We live in Central Arkansas. Last year this bug destroyed all of our Milkweed.

A: Milkweed bugs are native to much of the US, and very interesting milkweed herbivores. Their populations are generally too low to do much damage, but they do sometimes reach fairly high densities. You can find a lot of interesting information about them on the web.

Q: The University of Arizona has information on this pest. There is a site where you can purchase the Milkweed bug that Farmers may use to kill Milkweed in their fields. The site is

A: These are actually sold by Carolina for classroom rearing as an educational tool; I'm not aware of this species being used as a control agent for milkweed.

Q: The Monarch is in grave danger today. What is being done if anything from a protection perspective?

A: You can read about many actions to promote monarch conservation on the Monarch Joint Venture website:

Q: Do Monarchs sometimes roost off the Gulf Coast (Alabama?) instead of Mexico?

A: Yes. There are many Journey North reports of monarchs on the Gulf Coast during the winter.

Q: I have 6 just a couple of weeks old chrysalis. Our temperatures have been unusually high with 48 to 50 at night. I live along the coast in North San Diego County in Oceanside CA. Can these still hatch out? We have very bad rain coming.

A: Yes, they'll take longer under cool conditions, but they should be fine.

Q: I observe that monarchs migrating through Dallas, Tx have preference for the location of their selected milkweed host plant. It seems they like to have protection from the wind and morning sun afternoon shade. Is this so or am I missing something. I would like to know as my group would like to include milkweed into several large wildflower areas of historical park land and worry that the creatures wouldn't deposit eggs in full sun/open field.

A: I have found many eggs in full sun in open fields, but if it gets too hot monarchs suffer high mortality rates. This is probably a bigger issue in Dallas than in Minnesota, but large open areas were and are still very important to monarchs.

Q: Has there been any attempt to plant plots of milkweed in the overwintering tree groves of the western population within the United States? Such milkweed could be watered and protected by the same people who monitor the sanctuaries and insure that at least some of the monarch population has a secure wintering site and reproduction essentials.

A: Monarchs at the wintering sites are generally non-reproductive, and planting milkweed near these sites could affect their reproductive status. We do not recommend planting milkweed near overwintering sites, especially the non-native tropical milkweed which can allow breeding for generation after generation on the same plants, and thus lead to high rates of OE infection.

Q: Could the bodies of monarchs that die in the tree groves, either in California or Mexico, be collected and analyzed for chemicals from the scent glands on the wings? Then test the bark and leaves of the trees for similar chemicals. (Do the same test on leaves and bark of trees which are used for roosts during the migration.) If the butterflies do mark the trees, an extract of that chemical might be used to create new overwintering sites at altitudes where some milkweed plantings could also grow and the trees be protected.

A: This would be an interesting study.

Q: If you can tell the differences between the chemicals in the bodies of adults which are caused by the type of milkweed the larvae ate, can you do similar tests to see differences between the western and eastern populations of monarchs and on chemicals they leave on the host trees from the scent glands or excretion or some other marking process?

A: The eastern and western populations are genetically indistinguishable.

Q: Are there more monarchs in the spring or fall migration?

A: Because there is some overwintering mortality, there are more monarchs in the fall.

Q: How long is the fall migration? How long is the spring migration?

A: This varies with the starting point of the monarchs, but it can be as far as from Maine to central Mexico. The spring migration for an individual butterfly is not as long. The majority of monarchs coming out of Mexico probably only get as far north as about Kansas across to Virginia. Their offspring finish the spring migration.

Q: We hear so much about the migrating monarchs to Mexico, but what about the southern California Monarchs? Where do they go? Do they head up to northern CA? Or do they just live their life cycle here along the coast? (I am on the tip of San Diego and Orange County CA Coast) I grow milkweed year round and enjoy watching them survive. I just counted 25 cats on my milkweed last week.

A: Less is known about the important breeding grounds for western monarchs, but we know that at least some fly both north and east, with breeding occurring in northern California, Nevada, Colorado, Utah, and even into British Columbia.

Q: How much milkweed [in ounces or square inches of leaf surface] does it take to feed a monarch caterpillar from egg to chrysalis? That stat would come in handy when you try to guess how many caterpillars you can rear with a given amount of plants available.

A: This varies a lot with the thickness of the milkweed. For common milkweed, I always figure about one good-sized plant. They eat very small amounts as early instars, but the fifth instar can eat up to about 4 fairly good-sized leaves.

Q: This last year I have noticed orange and black bugs on my milkweed plants, they seem to be destroying the flowers and seed pods, how do I get rid of them without hurting the cycle of the monarch butterflies laying their eggs?

A: These are milkweed bugs, very interesting milkweed herbivores. Their numbers go up and down, and I would just let them be; they're native insects and won't kill the whole plants.

Q: I live in Virginia. I understand that east coast monarchs are less successful in migration. Is it still helpful to plant milkweed plants for the monarchs here to possibly bolster the population?

A: Yes, it's useful to plant milkweed anywhere that monarchs naturally breed.

Q: I have observed hornets attacking monarchs in the fall during migration. What are other common monarch predators? Is there something I can do to help the monarchs avoid predators? Should I try to reduce the predators and, if so, how?

A: Monarch eggs and larvae have many predators: ants, stinkbugs, spiders, lacewing larvae, ladybugs, etc. They are also attacked by parasitic flies and wasps. There really isn't anything you can do about these predators, but remember that monarchs have very high reproductive potential (one female can lay hundreds of eggs), so if there is sufficient habitat, enough can survive to carry on the population.

Q: Is there a way I can support monarchs in the Midwest on the main migration route--ie an organization to support with a donation or some other action I could take?

A: In addition to doing what you can to provide habitat, you can support monarch conservation organizations like the Monarch Joint Venture and the Monarch Butterfly Fund. You can also support organizations working to promote pollinator conservation, like the Xerces Society.

Q: I see that monarchs need high levels of lipids to successfully overwinter. Do the monarchs need a certain lipid level (or some other type of biological chemical level-- such as proteins or carbohydrates) to be able to produce viable eggs? Do scientists know what monarchs need to produce viable eggs?

A: Monarchs do use lipids to produce eggs and to survive. We don't know of a specific level needed to produce viable eggs, but if their lipid levels are low, they produce fewer eggs and have shorter lifespans.

Q: People have apparently helped spread monarchs to other parts of the world beyond the Americas where they originated. Have any of these populations had time to evolve into subspecies yet? Over time will they likely become new subspecies if they have not done so yet? What would cause monarchs to become new subspecies in these other countries? Might they eventually become a new species if enough time elapses?

A: Monarchs throughout the world are genetically very similar, reflecting the rather recent movement to other places. There are already subspecies, with Danaus plexippus plexippus in the northern part of the Americas, and Danaus plexippus megalippe in the Caribbean and Central and South America. Some authorities also recognize Danaus plexippus nigrippus as a separate subspecies in South America. One mechanism by which speciation occurs is by geographic isolation, so we would expect that the separate populations would become distinct enough to become separate species at some point, as long as there is no genetic interchange.

Q: I have read that monarch caterpillars like to leave the milkweed plants that they have fed on and climb to a different plant before forming their chrysalis. Are there particular types of plants they prefer to inhabit and if so how closely should these types of plant be located to the milkweed for the monarchs to use to pupate?

A: Monarchs pupate on many different kinds of plants and other structures. I've found them on blades of grass, spruce trees, park benches, fences, milkweed plants, and garage eaves. They rarely stay on the plant on which they were feeding, probably to avoid parasitic wasps that can use chewed leaves and frass as cues to locate their hosts. They can crawl several meters from their host plants. So the best answer to your question is that we really don't know!

Q: What is the difference in monarch migration density in Austin, Texas in fall compared to spring? We are trying to compare the similarities and differences of the two migration periods. Our observations tell us that the density of monarchs may be greater in the fall than the spring. We haven't been able to find a lot of literature for this question and thought you could provide some information that we could use with our research.

A: Yes, the densities of monarchs in the fall are higher. There are more monarchs then, before winter mortality occurs, and the densities probably seem higher too because they are coalescing as they migrate south rather than spreading out as they migrate north.

Q: One other question we had was about the migration season for fall and spring for Austin, Texas. What range does the research determine as a fall migration time period for Austin, Texas as well as a spring migration time period? Is there a standard range for how long each season lasts?

A: This is a little hard to pin down, because you have some fall breeding in the Austin area, which will draw out the fall migration. Also, it is variable from year to year. I would look at the Journey North animated maps from several years to really visualize the timing and variation from year to year.

Q: Do migrating monarchs in the fall lay eggs as far south as Austin, Texas? We observed 7 new caterpillars during the second/third week in October and these emerged from their chrysalises during the very end of the second week and into the third week of November. These Monarchs stayed for a number of days on our campus collecting nectar before setting off just ahead of our first real cold front. I've read that they do not lay eggs when they are migrating and want to see what you have observed or know about this.

A: Yes, there is a fair amount of research focus on this question right now. There is fall breeding as the monarchs move south in the fall. In most years, there isn't a lot of milkweed available, but in wet falls native milkweed can be fresh, and tropical milkweed that is planted and watered in gardens can also affect the degree of fall breeding.

Q: We have seen some kind of liquid drip from a chrysalis already. What would've caused that? The butterfly never emerged.

A: This is usually due to an injury.

Q: Will butterflies eat either milkweed or butterfly weed? If they start eating one, will they switch to the other?

A: Yes, both of these are milkweeds, and monarchs can eat both of them. In my experience, it is very easy to get them to switch from butterfly weed to other species, and less easy to do the opposite switch. Butterfly weed is not a preferred host plant.

Q: What other flowers are Monarch's favorites? I live in Zone 5a.

A: The most important thing is to make sure that you have flowering plants available throughout the summer. In my yard, monarchs love blazing star, iron weed, coneflower, New England and other asters, milkweeds of all kinds, and rattlesnake master. But I've seen them on many other species.

Q: Have the monarchs begun migrating north?

A: They started in mid-March, as usual!

Q: I live near Houston,TX and am concerned that a lack of milkweed for nourishment will seriously stress, and possibly kill, large numbers of migrating monarchs. Is there an available source of blooming plants that can be purchased and transplanted now? My local source does not have any available yet and a secondary source once had plants that were contaminated with insecticide.

A: Migrating monarchs can use many other nectar plants for nourishment, not just milkweed. But it's very important that you make sure that the plants you put in for monarchs have not been treated with systemic insecticides.