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Answers From the Monarch Butterfly Expert
Spring 2005
Courtesy of Dr. Karen Oberhauser

(Back to Monarch Butterfly FAQ)


Thanks for all of your great questions! If you'd like to learn more about monarchs, you might want to check out our two websites for basic information on monarchs:


Questions From: Mount Pleasant, Arizona
Mt. Pleasant Elementary


Q: We live in the edge of the Ozark Mountains. It seems the population of the Monarch has decreased. Is this due to our unusual changes in the weather?

A: Several biologists who study monarch butterflies recently came up with an answer to this question. Our names are listed below, and here are our thoughts.

Monarch populations fluctuate yearly from a combination of factors throughout North America. The following factors probably contributed to the current low 2004-05 population.

Winter mortality during the 2003-2004 seasons. The size of the spring migration is determined by the size of the migration the previous fall and the number of monarchs that survive the winter. It is likely that mortality from January 2004 storms in Mexico reduced the numbers of monarchs reaching the southern U.S. breeding areas in March - April. This may have resulted in a small wave of new first generation butterflies migrating to their northern breeding range.

Weather during the 2004 summer breeding season. The summer of 2004 in the mid-western breeding range was the coolest since 1992. Field and laboratory data indicate that eastern North American monarchs may produce up to five generations in a year with favorable weather conditions, but fewer generations in cold years. Cold weather hinders population growth by limiting oviposition and by extending generation time, thus limiting the number of generations.
Habitat deterioration of the overwintering sites. The condition of the forests in which monarchs overwinter is deteriorating through illegal logging. Opening the forest within or adjacent to the overwintering sites increases exposure of roosting butterflies to wind, wetting and heat loss that increase the numbers that freeze to death. These effects are exacerbated during storms.

Loss of summer breeding habitat. The principal larval food plant of the monarch butterfly in eastern North America is common milkweed. A 2000 study concluded that the majority of monarchs are produced on milkweeds growing within agricultural fields. Midwestern breeding habitat is being lost due to adoption of crops that are genetically engineered to be resistant to herbicides. Herbicides are sprayed in early spring, killing virtually all other emerging plants, including milkweed. In addition, herbicide use and habitat changes may be decreasing the availability of nectar sources needed during the fall and spring migrations.

Dr. Lincoln P. Brower, Sweet Briar College; Dr. Alfonso Alonso, Smithsonian Institution; Dr. Linda S, Fink, Sweet Briar College; Dr. Barrie Frost, Queens University, Canada; Dr. Stephen B. Malcolm, Western Michigan University; Dr. Karen Oberhauser, University of Minnesota; Dr. Isabel Ramirez, UNAM, Mexico; Mr. Daniel Slayback, Science Systems & Applications Inc.; Dr. Orley R. Taylor, University of Kansas; Dr. Stuart B. Weiss, Creekside Center for Earth Observations; Dr. Myron P. Zalucki, University of Queensland, Australia. Questions From: Diamond, Ohio
Southeast Intermediate School

Q: My class was wondering if there is any milkweed growing in the area where the butterflies are overwintering?

A: Yes, milkweed grows around several of the mountains on which monarchs overwinter.

Q: They also wondered if butterflies would be able to reproduce in Mexico before they migrate back north.

A: We do think that some monarchs that are part of the migratory population join a local population that is breeding in Mexico on native milkweed. However, we don’t think that these monarchs then migrate back north. One of my students, Eneida Montesinos, is studying the relationship between the Mexican and migratory monarch populations.


Questions From: Wooster, Ohio
Parkview Elementary School


Q: Are monarchs used for medicine? If so, how are they used?

A: No.

Q: Do monarchs get sick? If monarchs do get sick, what diseases do they have and how do they contract those diseases?

A: O. elektroschirrha (see answer to a question above) is only one of several parasites that infect monarch butterflies. Other parasites include tachinid flies, bacteria, fungi, microsporidians, and baculoviruses, although none have been well studied in natural populations.

Q: We know that the monarch migrations help certain areas in Mexico with the tourism business. How else can monarchs help people?

A: My life is certainly more interesting because there are monarchs! They delight and amaze us, and teach us about the wonderful ways in which organisms interact with their environment.

Questions From: Honolulu, Hawaii

Q: What do you think would be the reaction of butterflies if their winter Mexican habitat was totally destroyed while they were en route? Would they continue to look for their Mexican homes? Would they leave and seek out a new home? Would they lose hope, as whales and dolphins sometimes beach themselves? Thanks in advance!

A: We don’t know the answer to this question. Recent modeling work that I’ve done with Townsend Peterson at the University of Kansas showed that monarchs use very specific kinds of habitat in Mexico, and that habitat with the proper conditions is quite rare. So even if they do seek a new home, they may not be able to find it. However, monarchs in many other places in the world do not migrate like the Eastern North American population does (in fact you have non-migratory monarchs in Hawaii). It is possible that monarchs would respond to habitat deterioration in Mexico by changing their behavior. For example, they might not migrate, and instead stay in the southern US and breed throughout the winter. This is something that one of my graduate students, Reba Batalden, is investigating for her PhD research.


Questions From: El Sobrante, California

Q: I would like to know if you have the details of the butterfly's timing on their migration.

A: The best place to find details on the timing of the monarch’s migration is to follow their progress on Journey North! (See Monarch Butterfly home page.)

Q: I also would like to know if you know exactly when the butterflies will be in Santa Barbara, CA.

A: This varies from year to year. I do know that the important monarch population counts in California are conducted around Thanksgiving, and the colonies are fairly well-established in October.


From: Corinth, Maine

Q: I am a teacher working on a learning unit on climate change in the State of Maine. My colleague and I are interested in local indicators of climate change. Is there a data set sharing the dates (month, day and year) that Monarchs enter (in the spring) and leave (in the fall) the State of Maine? Yours, Margaret Chernosky, Bangor High, Bangor, Maine.

A: The Journey North website shows the entrance of monarchs into each state ­ (See archived maps) It is more difficult to observe when they leave, but in most northern states, there are few butterflies left after the first few weeks in September. We are also doing work on the potential effects of climate change in my lab at the University of Minnesota!


From: West Point, New York
West Point Elementary

Q: What effect do you think the new road they want to build in Texas will have on the Monarchs?

A: I’m not sure which road you mean. Sometimes roads are good for monarchs, because roadside ditches provide a good habitat for milkweed. However, a large road without natural plants growing in the roadsides could be a detriment.


From: Rolling Meadows, Illinois

Q: How big of a problem is the Ophryocystis elektroscirrha parasite in monarch butterflies? I know that this parasite can be ingested.

A: O. elektroscirrha has been reported from all monarch populations examined to date, but its prevalence varies dramatically among populations, probably because of processes related to monarch migration and parasite transmission. Monarchs from the eastern migratory population have lower infection rates than those from the western and southern Florida populations. The parasite does have measurable negative effects on monarch survival, both at larval and adult stages.

Q: Is there a way of confirming infected milkweed plants so they can be eliminated so not to cause further damage to the monarch population?

A: No. However, if milkweed is growing in an area where there is a continuously-breeding monarch population, the parasite can build up on the leaves. This won’t be a problem in Illinois, where the milkweed dies back each year.

Q: If not, is there any other way to prevent this type of infection from spreading to monarchs?

A: We are concerned about milkweed that may be continuously growing throughout the year. Without a die-back, the parasite has the opportunity to build up in a monarch population. For this reason, growing native milkweed instead of the non-native tropical milkweed in warm areas could prevent a build-up of O. elektroscirrha. It is also important to make sure that any monarchs that are raised in captivity and then released are not infected by the parasite.

This parasite is transmitted from mothers to offspring, or from males to females during mating. If these monarchs are infected, they will spread spores on all of your cages and other materials, and larvae that you raise next fall could be contaminated; if they’re released into the wild, they could infect other monarchs. You can read about this disease on the Monarch Lab website


Q: I have been reading about caterpillar defense mechanisms, and have come across a gland called an osmeterium gland that many caterpillars have and use to make them appear, or smell, less delectable to predators. Even though monarch caterpillars have bright coloration to forewarn predators of their poisonous make up, do they possess this gland?

A: This gland, which is extruded from an area just behind the caterpillar’s head, is not found in monarchs. It is found on swallowtails, which are in the family Papilionidae.

From: Keansburg, New Jersey
JC Caruso School



Q: When and where was the very first monarch discovered, who discovered it, and why was it called the "monarch" (we know that means king) butterfly?

A: We think that the name "monarch" was conceived because of the connection between William of Orange, a king of England, and the colors of the monarch butterfly. In 1797, it was called "the large orange-and-black butterfly" in the book “The Butterflies of Georgia,” and Robert Pyle, in his book chasing monarchs, said that the first use of the name monarch may have been in a paper written by Samuel Scudder in 1877.

Q: How fast can a monarch butterfly fly? We know the monarch can flap its wings up to 120 times a minute when being chased by a predator. We also know that a monarch uses thermals to fly high, and wind to fly fast, but our questions is how fast can it fly under its own power.

A: As you stated, this answer will depend a lot on wind and also temperature conditions. Sonia Altizer and Caterhin Bradley at Emory University in Georgia recently published a paper in which they reported the results of a study that involved measuring the flight speed of monarchs in the lab. When they weren’t tired (at the beginning of their time trials), they flew about 6 km per hour. They can probably fly faster outside, but it’s difficult to measure this under constant conditions. We do know that it takes them about 2 months to get from the northern part of their summer range to Mexico, about 3200 km.

Q: The question on everybody's lips is this: How does the tiny monarch butterfly know how to get to Mexico, and why don't all other butterflies go with them in the fall?

A: We don’t know for sure. We do know that they don’t learn where to go, but instead are genetically programmed to go to the right place at the right time. We also know that they use the sun as a cue to tell them which way is south. There is information on several questions about monarch migration, including theories on how they know how to get to Mexico, on the Monarch Lab website.

Unlike monarchs, many butterflies that live in places that freeze in the winter can withstand freezing conditions because they have “anti-freeze” in their bodies. Different species overwinter in different stages: as eggs, larvae, pupae or adults. Thus, they don’t need to leave. There are other migratory butterflies, but as far as we know, none fly as far as monarchs.


From: Oxford, North Carolina
Credle School


Q: Please list the Monarch migration sites in order from highest to lowest according to which sites have the most number of Monarch butterflies and also put the most current number of butterflies counted at each site. Thank you, Bobbie Lequire

A: These numbers vary from year to year, so I couldn’t answer this question with a single answer. Here are the numbers for this winter, which was the lowest ever on record. The measurements were made by Eduardo Rendon and other biologists working for World Wildlife Fund in Mexico. I’m listing the number of hectares occupied from lowest to highest, not the total number of monarchs counted, because it’s impossible to count the monarchs. Different estimates of the number per hectare range from 10 million to 65 million.

Sierra El Campanario (Rosario) 0.10
San Fco. Oxtotilpan 0.10
Piedra Herrada 0.14
Sierra Chincua 0.20
Cerro Pelon 0.24
Palomas 0.35
Sierra El Campanario 1.06

From: Fort Gratiot, Michigan
(homeschool)


Q: We are wondering if monarchs that go through metamorphosis in an indoor setting, such as a classroom or nature center, have the same ability to successfully produce young and migrate as those that develop outdoors. Do the sights, smells and sunlight a monarch experiences when it emerges from its chrysalis program it in some way? How much imprinting takes place at this time?

A: Several monarchs reared in classrooms and homes throughout the US have been found in Mexico, so we know that they can migrate successfully. We also know that they will mate and lay eggs in outdoor cages, but have never tracked them to know for absolute certain that they can lay eggs successfully in the wild.

Q: If a chrysalis was kept in total darkness, 24 hours a day, could it develop naturally?

A: No. We know that monarchs can sense and respond to light throughout their development. You may have observed that monarchs with exposure to natural light consistently emerge after dawn. This was recently tested by one of my students, who tested the influence of light on the time of emergence from the pupal stage. He “clock-shifted” a group of 15 pupae by 6 hours, now their “sunrise” was at noon and sunset was 2am. The butterflies in the experimental cage emerged approximately 6 hours after their comrades in a control cage. It turns out that butterflies have photoreceptors in their genitalia which form in the second half of pupal development. Thus even when the monarch is seemingly blind, the influence of light is important to their development. Ten studies on the influence of light and development were presented at our annual Insect Fair at the University of Minnesota. Students consistently found that lack of light negatively effected the development of their butterflies (see student abstracts at Monarch Lab).

Q: What mysteries about monarchs puzzle you the most?

A: My head is swimming with monarch mysteries! I would love to know how they find the exact same spots in Mexico every year; how they will respond to a changing climate; what determines what males are most successful at mating with females; how they find a single milkweed plant growing in the middle of a suburban grass “desert;” how they, of all species of butterflies and insects, have evolved the incredible migratory and overwintering phenomenon; and how they used their habitat before Europeans wiped out all of the prairies in the north and central US.

Dr. Karen Oberhauser
Department of Fisheries, Wildlife
and Conservation Biology
University of Minnesota

St. Paul, Minnesota
Monarch Lab


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