Answers From the Monarch Butterfly Expert
Spring 2009
(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 North Carolina
Q. Do Monarch's sleep?

A: Yes.

Q. Why do all Monarchs look alike?

A: If you look closely, they don’t! Their color patterns, size and even the number and size of white dots on the adult wings can vary.

From: Texas
Q. I see dozens of eggs laid on the milkweed. What factors/predators are preventing more of them from successfully becoming caterpillars? I live in Houston, TX and built a backyard pond around which I planted milkweed to raise Monarchs. Before my pond, I planted milkweed with a red/orange flower and had so many eggs/caterpillars I had a hard time counting them. Now, I have milkweed with a yellow flower and struggle to find three/four caterpillars a month that develop into a chrysalis.

A: There are many monarch predators. Ants, spiders, paper wasps, true bugs, lacewing larvae and several beetles attack them, and we estimate that fewer than 10% survive past the first instar.

From: California
Q. What is the "record" time for a monarch to stay in the chrysalis?
I found a Monarch larva last fall in a freezing rain. I brought it home since it was had not future otherwise. He pupated, then stayed in his chrysalis until Day 28! Why did he stay so long in his chryslais? How often does this happen?

A: I don’t know the record for time in the pupa stage, but it can be very long under cool conditions. The cool temperatures slowed your larva way down, and it must have taken it some time to recover.

From Missouri
Q. When the Monarchs are in flight how do they know where other Monarchs are roosting? Is the group in flight or a solo Monarch wanting to find a major roosting area? Rather a basic question but one that puzzles me. Looking forward to your reply.

A: This is really a great question. We don’t know the answer! It certainly seems that monarchs actively find each other at roost sites, but there may just be something about certain spots that attracts many butterflies. Elizabeth Howard and I spent a wonderful evening with some colleagues in northern Mexico last fall, finding mesquite trees with small congregations of monarchs on them. After a while, we could predict which trees would have monarchs on them, so it is possible that they are looking for specific characteristics and not other butterflies.

Q. Do monarchs visually see a bush in bloom or is it the fragrance that brings them down to nourish themselves? I have noticed Monarchs in flight over our house in prior a height of 80 to 120 feet over our 8 ft. butterfly bush, they start a sprial flight downward to the bush.

A: Another great question. Flowers have evolved to attract butterflies and other pollinators, and they use a combination of visual and olfactory cues to do this. My guess is that from that long a distance, the visual cues provided by your bush attract them.

From: Ohio
Q. Do you think the drought in Texas will have a big affect on the Monarchs reaching Ohio this year?
The cold wet spring of 2008 really delayed the Monarch migration to Ohio. The population was very small during the summer.

A: Yes, I’m worried about this. Texas is key to monarch populations.

From: North Carolina
Lincoln Charter School

Q. If reproductive diapause occurs because of shortening days and cooler temperatures, are we "ruining" our final generation by bringing them inside as larvae and pupae?
We have a Monarch Waystation at our school in the Piedmont of North Carolina. In late August we bring larvae into the classroom to watch them eat and then pupate. We then release the adults back into the garden.

A: It depends on whether the daylength to which they’re exposed is very different than it is outside. There are several records from the Monarch Watch program of recoveries in Mexico of tagged individuals that have been reared indoors in the fall, so unless you leave the lights on in your classroom there shouldn’t be a problem. To be safe, you could keep them near a window so they’re exposed to natural light.

From: Texas
Q. How can the migrating monarchs survive and reproduce once they are into areas still too early for plant growth? In our area (North Texas) 97.15 W and 32.68 N, monarchs can come migrating through before most plants have nectar and before any milkweed plants are available for egg laying and food for the larvae. Perhaps these food sources are available in south Texas and yet how can the migrating monarchs survive and reproduce once they are into areas still too early for plant growth? Note: I am not in an organized school situation, but am a school and park/nature center volunteer who is trying to educate people about monarchs.

A: Thanks for your work! Nature is such an incredible game of timing. The monarchs can’t survive without food, and can’t lay eggs without milkweed. I would guess that most years the timing is fairly good, but during years that plants are set back by cool weather, things can get out of sync. This is one of the observed impacts of climate change; the timing of breeding for many birds species is determined by daylength cues, but their insect prey respond to warmer conditions by developing faster. This can lead to food shortages if the insects aren’t in the right place at the right time for the birds.

From: Florida
Q. How many generations of Monarch butterflies on average does it take to migrate south and reach their winter homes?

A: For the most part, the butterflies that leave their breeding sites in the northern part of their range are the same ones that arrive in Mexico. This is not always the case, since some of them breed in the southern US. We assume that their offspring then complete the migration.

Q. What is the chemical in the milkweed that the Monarchs eat that makes it poisonous?
A: It is called a cardenolide glycoside, which is a steroid closely related to digitoxin.

Q. Has the Monarch genome been sequenced yet?
A: No, not the whole thing.

From: Texas
Q. There are too many eggs and caterpillars for the amount of milkweed that we have. Someone suggested refrigerating some of the eggs/caterpillars - is it possible to do this without harming them?

A: You can cool them for awhile at refrigerator temperature, but not for very long. We have found that eggs suffer fairly high mortality after about 6 days, but have never done similar experiments with larvae. One problem for the caterpillars may be the constant dark in the fridge. A refrigerator is usually about 4 degrees C; you can keep them alive for a long time at 10-12 degrees C.

From: Illinois
Q. I thought that Monarchs migrated to Mexico, or certain areas such as San Opisbo CA. How do you explain the Monarchs in Florida that look tattered and torn? Did they not make it to Mexico, and are they reproducing? Or where do they migrate to? Or have they already? I read some reports that other observers have written, and they have said they have Monarchs all year long.

A: There are monarchs all year round in Florida and other Gulf Coast states, including Texas. The degree to which the Florida populations are replenished with migrants from the north every year isn’t known, but there is genetic and other evidence they get an influx of migrants in the fall who then join the resident population.

From: Oregon
Forest Grove Community School
Q. Is there anything else we can do to help the Monarchs? We live in Forest Grove, Oregon (about 30 miles west of Portland). I have heard that our area once was a "flyway" for Monarchs migrating from California to Canada. This migration no longer happens in our area because the milkweed plants were pretty much wiped out. Our
' Roots&Shoots' group have planted milkweed plants in our butterfly garden for several years, as an effort to re-establish Monarchs to our area. Are there any organizations we could work with to further these goals?

A: There is a great organization called the Xerces Society which is working on conservation of monarchs in the western US. You can find out more about them at It sounds like your Roots and Shoots group is doing a great job, and even if you don’t have monarchs coming to your site, you’re providing habitat for other insects that are important too.

From New York
Q. Can you suggest ways I can rally support to preserve milkweed in its native habitat, especially urban areas? Who I can contact that will listen to this request? I really want to persue this issue!! I have raised Monarchs with Bronx, NY 3rd graders and just for myself. I have an ever increasingly difficult time finding milkweed to feed my larva and when I do find it, along parkways, open fields, itis either too difficult to harvest and or it gets mowed. I have tried to advocate with the Bronx Zoo, NY Botanical Gardens, NYC Dept of Transportation, etc, but there are "issues". Even locally in Westchester County NY, I was successful in contacting the Dept of Transportation and they agreeed not to mow but the local homeowner adjacent to the field had their gardener mow it! Other plants also seem to choke the milkweed.

A: First thanks so much for your tireless efforts. Sometimes, people just can’t be swayed, but often if you calmly try to explain to them that monarchs need milkweed it’s possible to convince them to accept it in neighboring areas and possibly even to plant it on their own land. You may want to try making some small signs to explain the importance of milkweed, or offering to give a talk to a homeowner or neighborhood group. One step at a time, we can change the world!

Q. I understand that it is difficult to cultivate, plant milkweed. Who can I contact to help me grow my own? I am working on a neighborhood planting project and I would love to plant milkweed this year. I need hands-on help!

A: Both the Monarch Watch and the Monarchs in the Classroom websites have information on growing milkweed, and there are lots of websites with milkweed seeds for sale. You can also plant a Monarch Waystation (as part of the Monarch Watch program).

Q. I tried to raise monarchs in late summer 2008 as I have done for about 6 years. I was so sad that none of my larva survived. It was devastating. I did all the same things I had done in the past. Is there something I overlooked this time? Thank you so very much for this incredible project. When I raised Monarch's with my 3rd graders in the Bronx it was a remarkable learning experience in so many ways for these kids.

A: Sometimes things just go wrong; you may have gotten a disease in the batch of larvae, or you may have picked some contaminated milkweed. This has happened to most people who raise monarchs at some point; I recommend cleaning all of your cages and other rearing supplies well, and trying again. If you got the monarchs from a supplier, it is possible that the disease came from their culture.

From Illinois
Q. What is the best way to grow milkweed seeds? I desperately want to have a full-fledged monarch "nursery" and garden this summer, full of common milkweed. I collected lots of pods last fall and now want to plant the seed. I have planted seeds in the past but no luck!

A: See answer to question 2 above. If you sow the plants in the fall, they should come up in the spring, but first year plants are smaller and you may miss them. You may want to set aside a place for the milkweed so you see it in the spring, or plant the seeds in pots. They do need to be cold-stratified.

From Ontario
Q. We have visited MEXICO the last 2 years and noticed a HUGE decrease in MONARCH population. Please explain.

A: There is lots of good information about the size of the monarch colonies at the Journey North website.. This year’s population was actually a little larger than last year’s. It’s not clear to me where you were in Mexico, but the numbers here suggest that there wasn’t a huge decrease.

From Maryland
Q. Do monarchs have iron in their blood and if yes, does it help them navigate using the earth's magnetic field? How?

A: Monarchs, and many other organisms, have some magnetite in their bodies, but there is no evidence that they use this for navigation.

From California
Q. How will the inscetacidal soaps work if there are eggs/catapillars in th milkweed as well?
Aphids are a big problem on milkweed here in southern california.

A: The insecticidal soap works by suffocating insects; it clogs their spiracles. So it would kill caterpillars that are present at the time of application. It would not result in long-lasting toxicity, though. I am working with a graduate student at the U of M who is studying aphids on milkweed and would love to talk with you about the timing and location of your aphids, especially if they’re the bright yellow oleander aphids (Aphis nerii). Her name is Emily Mohl (e-mail address

From Michigan
Q. I'm a Michigan resident just back from Mexico to see the butterflies. Is it known precisely where in Mexico our Michigan butterflies spend the winter?

A: Great that you got to see the colonies! There is no evidence that monarchs from particular parts of the country go to particular locations in Mexico, so you could have been seeing “your” monarchs at any of the sites you visited.

From Virginia
Q. Can you tell the gender of the butterfly from the chrysalis?

A: Yes. We wrote about this in our 2005 Monarchs in the Classroom newsletter. There’s a link to the article from this page on our website

From New Jersey
E.T. Hamilton Elementary School
Q. Was it alot of fun to go to the monarch butterflies part time home in Mexico?

A: Yes, I love to visit their part-time home in Mexico. I love to study them in Minnesota too!

From: Texas
Q. I'm a lady sailor and we've named our racing team, Team Monarch. Can you describe how the Monarchs use and articulate their wings to maximize the wind in their flying and gliding.

A: I love your team name. Butterfly flight is amazing, and there have been some really interesting papers on the mechanics of their wings during flight. One of the clearest and most interesting that I’ve read is called “Vortex Formation in the Tethered Flight of the Peacock Butterfly Inachis io L. (Lepidoptera, Nymphalidae) and some Aspects of Insect Flight Evolution” by A.K. Brodsky. You can easily find it on the web; it’s published in the journal of Experimental Biology.

Q. How do they choose good days to fly? Sometimes I see them flying
into headwinds and making more sideways progress than forward.

A: That is a really interesting question. They can find elevations that maximize flight efficiency; if it’s very windy (in the wrong direction) they often seem to stay close to the ground. They probably can’t afford to miss too many days; in a sense they’re racing against time to get out of the north before all of their nectar sources freeze and it becomes too cold for them to fly.

From New Hampshire
Q. What do you know about monarch butterflies as animal spirit totems/ guides? Have you even heard of totems? If so, I would greatly appreciate any information you had on butterflies as totems.

A: Sorry, I don’t know anything about this topic.

From: Journey North's Elizabeth Howard

What is OE?

OE is a disease that affects monarch butterflies. OE is a parasite. Its scientific name is "Ophryocystis elektroscirrha" so it is called "OE" for short. For more information about OE see the Monarch Health website.

Q. Many people in the southern U.S. are now growing Mexican milkweed in their butterfly gardens because it is hardier than native milkweeds and, in some climates, available for monarch reproduction all winter. If this milkweed does not die back in the winter, the way native milkweeds do, are you concerned that levels of Oe could rise to levels that are found in Florida and other places where milkweed is available year-round?

A: Great question, Elizabeth. Yes, we are concerned about this. There is good evidence that Oe levels are higher in areas where milkweed doesn’t die back. However, these also tend to be areas in which monarchs don’t migrate, and Oe infestation levels are higher in non-migratory monarch populations. So we don’t really know what’s cause and effect here; both continuous breeding and milkweed that doesn’t die back are associated with high Oe levels, but correlation doesn’t always mean causation.

Q. I visited a school in the monarch overwintering region that is located about 1 km from the Sierra Chincua monarch sanctuary. The teachers there had visited the U.S. and were excited about raising monarchs at their school the way they had seen in the U.S. They were also going to grow a garden with Mexican milkweed. Would you have concerns about this? Thanks Karen! Elizabeth Howard

A: Yes, I’d be concerned about this too. While monarchs are wintering, they are in a special, non-reproductive condition called diapause. There is some evidence that the presence of milkweed can hasten diapause development, which means that the monarchs might become reproductive sooner than they would otherwise. Depending on how much milkweed was around and how close it was to the colonies, this could have an impact on the population, possibly changing the timing of their departure from the colonies or even keeping some in Mexico. However, one small garden may not have much of an impact, and might provide a great educational experience. There are always tradeoffs….

There is actually some milkweed naturally available not far from the colonies, and I’ve seen eggs and larvae on this milkweed in February. We don’t know if the monarchs that laid these eggs were from the migratory population, or if they were part of a resident, non-migratory Mexican population.