Answers From the Monarch Butterfly Expert
Spring 2003

Courtesy of Dr. Karen Oberhauser
(Back to Monarch Butterfly FAQ)


Special thanks to Dr. Karen Oberhauser, University of Minnesota Department of Ecology, Evolution and Behavior for providing her time and expertise in responding to your questions below.


From: Wintersville, Ohio

Q: I rear monarchs for release. Last year I had 7 that fell almost immediately after hatching. 3 of them I was watching and put them back onto a stick and they continued to dry their wings and fly. 3 I did not see and their wings were deformed and they eventually died. One I put back on a stick and he seemed to dry well and opened and closed his wings several times, but was dead the next morning. What happened to them that they could not hang on until their wings were dry? Thank You Sue Mitchell

A: While I can't be sure about what happened without seeing the butterflies, there is a good chance that the butterfly that you put on the stick that still died was injured when it fell. Even though his wings dried normally, he may have had some internal injuries that ended up killing him.


From: Levittown, NY
Levittown Memorial
Gr 3 Gifted Program

Q: A teacher in Levittown, NY recently visited Pacific Grove, CA (Butterfly Town, USA) and visited the Butterfly Sanctuary. Unfortunately there were VERY few monarch butterflies. Might this mean that the butterflies in Mexico might be having a bad year as well?

A: Even though there is recent evidence that there is some exchange of butterflies between the eastern and western migratory populations, it is most likely that regional environmental conditions (including both "natural" and human-caused conditions) affect the populations separately. As it turned out, numbers in Mexico this winter were well within the range of numbers that have been observed over the last several years.



Photo: Virginia Cooperative Extension
From: Hattieville, Arizona

Q: We plant a lot of milkweed for the Monarchs. Before summer is over our milkweed usually has a lot of the yellow aphids on it. Is there a safe way to get rid of the aphids without harming the caterpillars?

A: You definitely should not use any toxic insecticide, since that could kill the caterpillars as well. You can wash the aphids off by hand with a mild soap solution or use an insecticidal soap, but these solutions will kill caterpillars that are present during the actual application. The insecticidal soaps act by clogging the spiracles on the insects' bodies, essentially smothering them. They are not toxic in the sense that they poison the insect.

Q: If there are a lot of aphids can the eggs and caterpillars still live or do the aphids actually eat the caterpillars or destroy the milkweed so bad it causes the caterpillar to die? I really want to have a successful environment for the Monarchs, so any helpful tips would be greatly appreciated!!!!!

A: If the aphids are so abundant that they affect the health of the plant, this could harm the monarchs. A few aphids on the plant do not hurt the monarchs, though. There are interesting indirect interactions between the monarchs and aphids. Many aphids (but perhaps not the yellow ones you're seeing) are tended by ants, and the ants will kill monarch larvae. Thus the aphids have an indirect negative affect on the monarchs.

Q: Do green tree frogs eat the caterpillars or do they clean up the aphids?

A: I don't know! I see a lot of these frogs on milkweed plants, but have never seen them eating either monarchs or aphids.


From: Birmingham, Alabama
Inglenoook Elementary

Q: After the males have mated with the female, do they migrate or usually die there? I know the females progress to lay eggs but wondered about the male population after mating there. Thank you.

A: Males migrate after mating, unless they die for reasons that are unrelated to mating.


From: St. Louis, Missouri
Sappington School, LEAP program

Q: Do monarchs have mates?

A: They have mates in the sense that they need to mate to fertilize the eggs that will become the next generation. However, like most insects, there is no long-term relationship between and male and female that mate with each other.

Q: If they do, are they lifetime or not?

A: Once they've finished mating, they usually just go their separate ways!

Q: If they are lifetime, how do they tell which butterfly is their mate?

A: Since they don't maintain pairbonds, they don't need to "remember" which is their mate.


Photo: Karen Oberhauser
From: Rock Island, Illinois
Audubon Elementary

Q: This year the monarch eggs and larvae that we collected did well, we raised and released 75 adults. However our question is about several that were deformed because this is the first time we have seen so many. Their wings did not open to full size thus they were not able to fly. The rest of their life cycle seemed normal. We compared the collection time and site and found they were not from the same place, although 3 emerged within 24 hrs. Question: Does raising in captivity affect their ability to change from larva to adult normally? We wondered if the inside air conditioned room (70-72degrees), difference in humidity, or other factors caused the problem.

A: Usually, monarch survival is much higher in captivity than in the wild, where predators and other factors result in the death of about 90% of the eggs that are laid by females. You don't say the number of deformed ones that you had relative to the 75 successful ones, so I can't really tell if you had unusually high numbers of deformities or not. If you had 10 or fewer, I think that things were probably fine in your classroom. If not, you might want to try to figure out what was going wrong.

Q: We try to keep track of eggs/larvae collected and how many reach adulthood successfully. Do you have an estimate of the survival rate in the wild?

A: Fewer than 10%! You can check out the numbers on our Monarch Larva Monitoring Project website . Our latest newsletter, which is online, has a discussion of mortality in the wild.

Q: If you rear them, what is your survival rate? Thank you for sharing your expertise with teachers and students who are very enthusiastic about the project.

A: We have survival rates of about 90-99% in our lab. The lower rates occur when we are rearing large numbers in cages, and probably result from them eating each other inadvertently.


From: Middletown, Connecticut
Keigwin Middle School

Q: Why don't the monarchs die or get sick when they eat the milkweed during the caterpillar stage?

A: Monarchs have evolved to be able to tolerate the toxins in the milkweed. However, several studies have shown that milkweed species that have very high levels of toxins are harmful to the monarchs, and that they do best on species with moderate amounts of toxin.


Dr. Karen Oberhauser
University of Minnesota
Department of Ecology

1987 Upper Buford Circle
St. Paul MN 55108
612 624-8706 fax: 612 624-6777


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