Answers From the Monarch Butterfly Expert
Spring 2013
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Special thanks to Dr. Karen Oberhauser for sharing her time and expertise again this year to answer readers' questions.

Dr. Oberhauser is a professor at the University of Minnesota. She is also director of two citizen science projects,the Monarch Larva Monitoring Project and Monarch Lab.

Dr. Karen Oberhauser

Q: Can butterflies hear sounds?

A: In general, butterflies have very poor hearing. They can often sense sound through veins in their wings, but this has only been studied in a few butterfly species. Larvae can sense sound through small hair-like projections on the surface of their bodies called tactile setae. The setae sense vibrations in the air.

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: When the newly emerged adult monarch pumps fluid from the abdomen into the wings, does the fluid remain a liquid in the veins or do the veins of the wings become solid after awhile?

A: Blood flows through the wings even after the wings have hardened. Blood flows from the thorax into the wings, and then back into the thorax.

Q: What happens if a female mates and is ready to lay her eggs and can't locate milkweed? Does she lay them on any plant she finds? If that is so, what becomes of the caterpillars?

A: Females will wait a long time to find milkweed. Sometimes in our cages we keep mated females without milkweed, and VERY rarely, we will find a few eggs on other plants or the sponges we use to feed the females. The caterpillars then die. That's a bad situation for females to be in, and their reproductive cycle is closely coordinated with their environment so that it doesn't happen too often. We have done studies here at the University of Minnesota of females that were overwintering in Mexico. The studies have shown that having milkweed around actually speeds up egg development.

Q: We see dozens of eggs laid on our milkweed. What factors/predators are preventing more of them from successfully becoming caterpillars?

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.

Q: Does any structure of the caterpillar survive in the chrysalis? Is it a gelatinous mass?

A: While the popular metaphor of "pupa soup" or "gelatinous mass" composed of broken down larva body parts is often used, this is a gross oversimplification of an amazing process. At no time between egg fertilization and death do all body parts break down. Some do, but many don't. 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.

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.

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 broken down by enzymes early during the pupa stage. These broken down muscles do form a liquid within the developing pupa.

Q: Does the skin of the chrysalid play a significant role in the formation of the wings and other organs? We have been "raising" Monarchs in our yard for about 12 years. I try to video the whole cycle. I notice that, during the first week of a chrysalid, it looks like it is empty, except at the top. This is why I have always wondered if the skin, itself, of the chrysalid, plays a significant role in the formation of the wings and other organs. I think this because of the immediate visible pattern of the wings, etc. on the skin. It appears that the wings grow from the skin inward. Is there a lining against the inner skin that begins to form the wings?

A: The skin (or exoskeleton) of the chrysalis is shed, in a way similar to that in which the exoskeleton of each of the previous larval instars is shed. While it may appear that the wings and other organs grow from the skin inward, they are actually present in the larva, and grow continuously in the last larval instar. During the wandering stage (after the larva has stopped eating), the tracheal system that fills the wing veins develops, and as the larva pupates, the wing assumes the shape that it will have in the adult. The inner layers of the pupal exoskeleton, just like the inner layers of the larval exoskeleton, does break down before the butterfly emerges (that's why it looks thinner at the end of the pupal stage) and some of its component nutrients are used by the developing butterfly, but the wings are not actually part of the exoskeleton.

Q: Can cold temperatures cause monarchs to emerge with deformed wings? We are in Louisiana and trying to have monarchs breed all winter. Some of the Monarchs are emerging but their wings are slightly bent. Is it because it is cold? There are still a couple of chrysalises that look healthy, but most don't.

A: It's possible that the cold temperatures are causing the deformed wings; temperatures that are outside of the optimal development temperatures (either too cool or too warm) can cause problems for the developing butterfly. However, if you are breeding monarchs year around, you definitely run the risk of having the protozoan parasite Ophryocystis elektroschirra (OE) infect your monarchs, and OE also can result in deformed wings. You should definitely check, especially if your pupae don't look healthy. To find out how to have your monarchs tested, you can go to the website This project is a citizen science project run out of Dr. Sonia Altizer's lab at the University of Georgia.