Answers From the Monarch Butterfly Expert
Spring 2008
(Back to Monarch Butterfly FAQ)

Special thanks to Dr. Oberhauser for providing her time and expertise in responding to your questions below.

Dr. Karen Oberhauser

From: Saskatchewan

Q: Are a monarch larva's "stripes" as unique as fingerprints?

A: The stripes actually have a very similar pattern from larva to larva, although there is definitely individual variation. This would be an interesting question for a student research project!

Q: Why do monarchs have such a bitter taste to animals?

A: Cardenolides, the compound that make monarchs toxic, comes from the milkweed they eat as larvae. And it’s the cardenolides that give monarchs their bitter taste. It’s also what makes monarchs toxic to vertebrates.

From: Minnesota

Q: I don't know of any other species that seems to have such a variation in life spans from generation to generation. What is it that allows one generation (the one that migrates south, winters in the sanctuaries, and then, females only, flies north to lay eggs) to live so much longer than the succeeding generations who continue the journey north? Is it just that the hibernation period, which lasts several months, just doesn't "age" the butterflies?

A: Monarchs that migrate go into a reproductive diapause, meaning they do not mate or lay eggs. Reproducing takes a lot of energy, and the energy saved is stored as fat so the monarchs can survive through the winter. In the spring, they break diapause, mate, lay eggs, and then their offspring continue the journey north. A monarch that migrates (and enters diapause) lives for about six months, whereas a monarch that does not migrate only lives for about one month.

Additionally, the cool weather in the overwintering sites slows their metabolism, allowing them to live longer.

Q: Is it something in the difference in the DNA that exists from generation to generation?

A: No, there are not genetic differences between the migrants and non-migrants.
From: Pennsylvania

Q: Do monarchs avoid mountains during migration?
I do have an observation that I have noticed for several years. I watch the spring migration of the monarch and the ruby-throated hummingbird. The online maps show the progression of each. I have noticed that in the spring the monarch and the ruby-throat avoid the mountains through West Virginia and Pennsylvania. Do you have an explanation?

A: Mountains are barriers for many migrants; it’s amazing to look at Journey North migration maps and see how monarchs avoid them. For one thing, montane habitats don’t support a lot of milkweed, and also tend to be cooler, so species that aren’t specifically adapted to these conditions won’t do as well in them. Montane conditions usually support very specific plants and animals.

From: Michigan

Q: Do male Monarchs migrate north from Mexico?

A: Yes, the males migrate too. While females do sometimes mate in the Mexican colonies, they usually use sperm from the last male that they mate with, so it’s to the males’ advantage to move north with the females.

Q: What makes for survivors...a lot die in Mexico...many live to migrate north.

A: Since food sources are scarce in the overwintering sites, monarchs that don’t have enough fat stored will die, and there is some predation from mice and birds, too. Weather also plays a role. If it’s too warm, the fat they have stored is used quickly, and if it rains or gets too cold they freeze and die.

Q: In the Monarch population at large is the ratio of males to females changing?

A: The sex of monarchs is the result of genes on X and Y chromosomes, just like for us. Although in butterflies the males are XX and the females are XY. Females lay eggs in approximately equal sex ratios, so this should stay constant.

From: New Jersey

Q: How is global warming affecting the Monarchs and/or their migration?

A: We have a graduate student doing research to answer that same question! She’s finding that higher temperatures do increase mortality, and that monarchs may have to migrate farther north to maintain the same climate type they live in now. One concern is whether or not the milkweed will be where the new monarch range will be. Without milkweed, the monarchs won’t be able to survive.

Q: If there is another ice age, would the Monarch population become extinct or would they travel further south?

A: It’s hard to say, and would depend on the extent of the cold conditions. Monarchs have been able to adapt to a wide variety of climatic and seasonal conditions throughout the world, so it’s possible that they could move south.

From: Texas

Q: How long have monarchs been present on Earth? Is there evidence that tells you they have always migrated to survive the winter?

A: Based on fossil records, the first winged insects appeared approximately 350 million years ago. However, butterflies were not in this group. Rather, they first appeared about 175 million years ago. Keep in mind that these are estimates based on the fossil record. Some insect bodies are more likely to fossilize than others, and where an insect lived can also affect the fossil record. These numbers are good estimates, but we may never know precisely how long butterflies have been around.

Q: How do monarchs communicate with each other?

A: Monarchs are usually only together when they mate. Other than that, they live alone. Because of this, they probably don’t need a way of communicating with each other.

Q: If the oyamel forests are not protected, do you think that the monarchs will adapt to another species of tree or winter habitat?

A: It’s not necessarily the tree species that’s important, it’s the microclimatic conditions in which the trees grow. Monarchs winter in very specific microclimatic conditions, which are found on the Mexican mountaintops where they form their colonies.

From: California

Q: About 4 years ago a wild California spring migrant was recaptured in Pueblo, Colorado (east of the Rocky Mountains). Last week, a wild fall migrant tagged in Arizona was recaptured in Michoacan (east of the Rocky Mountains). Last August, Paul Cherubini posted photos on Journey North of many monarch caterpillars found at high altitudes in south-central Colorado (7,700 - 8,511 feet). In Feb. 2000 on the dplex-l, Paul Cherubini posted data on 6 monarchs tagged in western Colorado on Sept. 15-17, 1999 that were recaptured in Michoacan in Jan. 2000. In view of this information, is it reasonable and accurate for Journey North and the monarch scientific community to claim there are "geographically distinct western and eastern monarch populations"?

A: While it has often been assumed that the eastern and western North American populations are separated by the Rocky Mountains, recent evidence suggests that some western monarchs move south and southeast, entering the Mexican state of Sonora from Arizona (Pyle 2000, Brower and Pyle 2004). It is possible that some degree of genetic interchange occurs in Mexico and within the Rocky Mountains during the breeding season, preventing complete separation of the two populations. This information is included in the recent Monarch Butterfly Migration and Conservation book edited by Oberhauser and Solensky, as well as the publications mentioned above, so it’s not the case that the whole monarch scientific community claims there are "geographically distinct western and eastern monarch populations". However, most scientists would agree that the Rocky Mountains provide a barrier for complete intermixing of the two populations, and that there is some degree of distinction between them.

From: Massachusetts

Q: We would like to learn more about how the Monarch finds its way to Mexico. Does it navigate using the sun or the earth's magnetic field? What else is involved? How does its body detect the earth's magnetic field? Could you send us some information and Internet sites to learn more. Thanks.

A: This is one of the great mysteries of monarch butterflies. We know that monarchs use the sun to navigate, but we don’t know the details of fine scale navigation. There is little evidence that they use the earth’s magnetic field. You can read more about monarch navigation strategies at Monarch Lab.

From: Florida

Q: I live on the east cost of Florida in central Brevard County. If I had 20-100 acres what type of Habitat could I develop? Could I attract winter and spring migrations of butterflies?

A: You could plant tropical milkweed (Asclepias curassavica) as part of a butterfly garden, as well as other milkweed species that are native to Florida. You should also include other plants that flower, trying to get species that flower at different times of the year so that monarchs and other butterflies will always have something to eat. There are excellent maps of the spring and fall migrations on the Journey North website, and you can look at the Monarch Larva Monitoring Project website at to see if there are monitors in your area. If no one near you is monitoring, you can sign up to join the project, which involves monitoring a milkweed patch at least once a week and entering the number of eggs and larvae you see onto the website. Even if you don’t find any monarchs in your new butterfly garden, that information is still important. Either way, your data could help understand monarch use of habitat in Florida.

From: California

Q: Does it hurt monarchs if I use neim oil to control aphid pests in my garden?
I live in coastal San Diego ( 4 blocks to the beach) and have a large monarch habitat full of tropical milkweed. They are often full of aphids which seem to weaken the plants. I am very aware of pesticides (landscaper) and not using them in the area at all. However, I was wondering if there have been any tests using neim oil (from the neim tree 100%) to rid the area of aphids. I did a small test on a few caterpillars & they seemed indifferent & kept eating. I did not see if they lived to fly away however. I also wonder what it will do to the eggs.

A: I’m not sure if anyone has looked at the impacts of neim oil on monarchs. Aphids are definitely a problem, but any pesticides that you use might harm the aphids’ natural predators and actually make the problem worse.

From: Indiana

Q: We would like to know the best place and time to purchase milkweed plants and monarch caterpillars for planting and release in the spring.

A: You can purchase milkweed seeds online from a number of places and plant those in trays. I do not recommend specific growers for monarch larvae.

Q: Do monarchs have a favorite kind of milkweed plant?

A: The milkweed species that monarchs use vary with location. There are different species in the southern and northern part of their range. They use many species; the best thing to do is find species that are native to your area, and plant them. You may want to try a few species. A. syriaca (common milkweed), and A. incarnata (swamp milkweed) are always good bets, but there are many other great species to try. Butterfly milkweed (A. tuberosa) is not a good choice for larval food plants because the leaves are quite hairy, but it is a great nectar source.

Q: How do you raise Monarch caterpillars?

A: Visit Monarch Lab for a how-to guide on raising monarchs.

From: Ohio
Q: For the past 10 yrs. I have had a good patch of common milkweed plants in an area of about 8'x8'. Last year the plants were mostly stunted and not reaching maturity. Could this be because they have been confined to a small area for so long? Would it be best to start new plants?

A: It is a possibility. Depending on the density of the milkweed in that area, there might not be enough nutrients in the soil for all of the plants. You could try thinning out some of the plants to see if that helps, or you could add compost to the soil to add nutrients. Here in Minnesota, last year was somewhat dry; if that was the case where you live, that may have been a contributing factor.

From: California
Q: Monarchs were hatched in my garden in Southern California (San Diego) this year. They fed on Asclepias curassavica. The two that I saw never managed to zip their tongue to be able to feed. Both were unable to feed. What is going on? When do newly hatched butterflies zip their proboscis? I hope you have an answer, as more caterpillars are on the plants right now.

A: I think you’re asking about how the proboscis is split when adults first eclose. Eventually the two halves come together to form a straw-like projection and the monarch is able to eat. This happens very soon after the butterfly ecloses, but in some cases it fails to happen. I don’t know why. When the two halves don’t zip together, the butterfly can’t eat.

From Minnesota

Q: Why do they fly in a zig zig pattern, instead of straight ahead? Is it a way of evading predators?

A: If you see this behavior in a milkweed patch, the monarchs are probably flying this way to find nectar or plants to lay their eggs on. It’s possible that male monarchs are searching for a mate.

From: Lexington, Massachusetts

Q: Do Monarchs that begin migrating south from northern-most areas cycle through generations on the way? Or do they make the whole migration as adults?

A: When monarchs fly to Mexico, they do so in one generation. But when they are flying back to the Northern U.S. they do so in two generations. The monarchs that overwintered in Mexico mate and lay eggs in the Southern U.S. and then the offspring continue the migration north.

From: Pennsylvania
Q: For 2 yrs monarchs have laid eggs on my butterfly weed plants in my front yard. They hatch into caterpillars. I saw 11 in 06 and 6 in 07. I never see the next stage. It's like they get pretty big and just disappear overnight. I look around the area for a place they might attach themselves but I don't see anything. The closest tree is a flowering cherry and it’s about 8 ft away. How could they just vanish?

A: Actually, it’s rare to see a chrysalis on a milkweed plant. The tree is a likely target, and even though it’s 8 feet away, they are still able to get to it. We’ve heard stories of people seeing larvae travel farther than that to pupate! Also, over 90% of eggs and larvae are eaten by predators before making it to the pupa stage, so when they disappear an ant, beetle, spider, lacewing larva, predatory bug or some other predator might be the culprit.

From: Westland, Michigan

Q: It was asked at one of my meetings, "How far do Monarchs travel from where they are raised". I have introduced raising Monarchs to my members and they wanted to know, here in Michigan, how far the Monarchs they raise will travel. I told them that I didn't know and that only a few, of the hundreds that I raise, actually stay near my home. Do you have any idea how far from where they are raised they travel?

A: (I assume that you mean non-migratory monarchs.) We really don’t know a lot about movements of non-migratory monarchs. In my anecdotal observations, females seem to be less likely to stay in one place, whereas I have seen males over and over at the same milkweed patch. I’ve recovered them over a km from where I released them, but I’m sure they’ll travel much farther.

From: Holmen, Wisconsin

Evergreen Elementary Garden Club
Q: Even though Monarchs are genetically programmed to return to the area they came from on their "Journey North", do they ever go past that area? We live in West Central Wisconsin and were wondering if any of the descendants of the Monarchs that started out here last summer and migrated south, head back this way, but keep going Northward to reach the Canadian border? And if they do, does sunny, warm weather have anything to do with it?

A: I’m not sure where you learned that monarchs are genetically programmed to return to the area from which they came, but there’s no good evidence that this is true. Since monarchs from all over their northern breeding range are together in Mexico, and fly northward together, they mate with butterflies from all over. Thus, if this theory was right, where would they return to – their mother’s point of origin or their father’s?

Q: What is the correct plural for Chrysalis? Is it chrysalises or chrysali? Or are they both correct? I try to incorporate a lot of vocabulary into our garden club meetings. We have studied the Monarch Life cycle each year for the past four years and this is a recurrent question from my students.

A: Actually, it’s chrysalides. I know it’s weird. I can’t think of any other word that follows this same pattern.

Q: In the summer of 2006, I noted not just one monarch larva per plant but instead each roadside plant in Northern Wisconsin near our cabin were "loaded with caterpillars". I have the pictures to prove it! I thought this was unusual. Was it?

A: I would say it’s unusual, yes, but there are definitely cases of this occurring in other places. Females generally only lay one egg per plant, perhaps to give their offspring a better chance at surviving. Perhaps a bunch of females liked those plants and they all laid one egg! Or perhaps there wasn’t a lot of milkweed around, so females kept coming back to the same plants. There isn’t good evidence that females can detect eggs that are already on a plant, so the way that they avoid laying multiple eggs on a plant is by laying one at a time, and then flying in a straight direction to another plant. This avoids overcrowding. However, when we put monarch females in cages, they’ll lay 100’s of eggs on the same plant.