Ecology
Contributed by Dr. Karen Oberhauser
Includes
- food
- habitat and range
- niche
- enemies
- adaptations
- migration
- populations
- distribution
- ecosystems
Food
Q. What do monarch butterflies eat?
A. Adult butterflies eat nectar and water. Sometimes liquid from fruits. Larvae eat only milkweed.
Q. What color is nectar? Is it always the same color for each flower or does it change colors?
A. This is a GREAT question! In my experience, nectar is usually clear. I’ve never seen any that was the color of the flower, but I haven’t looked at nectar from every flower species. This would be a fun thing to test. You could get a very fine capillary tube, like the kind that they use to draw blood after they prick your finger at the doctor’s office, and put it into a flower. You will then be able to see what color the nectar is.
Q. How do monarchs eat?
A. Adult monarch butterflies sip nectar from flowering plants using a sucking tube, that resembles a soda straw, and is called a proboscis. You can see it coiled under its head when not in use.
Q: Where does the monarch butterfly fit in the food web is it is considered poisonous by its predators due to the fact that it eats milkweed?
A. Good question! You must be taking an ecology class, or have an excellent science teacher! It turns out that most biologists have studied the predators of adult monarchs, and not the larvae. Many insects, spiders, and other invertebrates eat the larvae, so monarchs are like other herbivores; they eat plants, and are in turn eaten by predators.
Q. Do the males look for food more than the females?
A. I don’t think so, but I’ve never studied this nor read about anyone else’s study of this question. How could YOU answer it?
Enemies
Q: What is the name of the poison in the monarch butterfly’s body and how potent is it?
A. The monarch stores a poison called cardenolides, or cardiac glycosides that it gets from the plants it eats. This poison is similar to digitalis, which can be used to help people with heart problems, but can kill people if they consume too much of it. These are poisonous to most vertebrates (animals with backbones), but they may not be poisonous to invertebrates (animals without backbones). The potency of monarchs depends on the potency of the plants they ate when they were caterpillars. Some kinds of milkweed have higher levels of cardiac glycosides than others. The effect of the toxin depends on the amount of toxin that the predator eats, and what kind of animal the predator is.
Q. Are there any that can and do regularly eat monarch butterflies or caterpillars?
A. Yes. There are some birds that eat monarchs, some mammals (mice), several insects, and some parasites. We don’t know much about the insect predators, but the birds have evolved interesting ways to handle the toxins in monarchs.
Q. What are some invertebrate predators of the monarch and why are they able to eat the monarch since birds can’t?
A. Briefly, many insects (stink bugs, wasps, ambush bugs are some) eat monarchs. We don’t know how they deal with the toxins.See the Monarch Watch homepage. We have a good section on this.
Q. If the monarch butterfly is toxic to the two predator birds, what effect does the toxins have on the mice predators?
A. The two bird species that eat monarchs in the Mexican overwintering colonies have probably evolved to be able to tolerate the toxins, and this is apparently true of the mice as well. Of five species of mice that are common around the overwintering sites in Mexico, only one eats monarchs, Peromyscus melanotis, the scansorial black-eared mouse. These mice have somehow overcome the monarchs’ chemical defenses enough to use them as an important food source during the winter. I’m not sure just what effects the toxins have on the mice, but they can’t be too bad, since the species that eat the monarchs seem to do very well eating them. In fact, one mouse can eat about 37 monarchs a night. In two different summers, mice have eaten monarch pupae that were in cages that I was keeping outside in Minnesota. I don’t know if this made the mice sick, however, and as far as I know, no one has studied whether these particular mice are important predators of monarchs.
Q: Approximately how long does it take predators’ bodies to eliminate/reduce the toxin levels to a safe level or to where they can eat again?
A: This would vary a lot with the size and species of the predator, and hasn’t actually been studied very much. We do know that some predators seem to be able to tolerate the toxins in monarchs with very few problems.
While scientists have studied the timing of bird predation (it occurs twice a day in the overwintering colonies), I’m not sure if anyone has actually followed a particular bird to see if it eats monarchs twice a day. Maybe individual birds do need to wait a while after eating monarchs. The orioles that eat the monarchs actually avoid the toxins by not eating the cuticle (skin) where most of the toxins are stored. The grosbeaks do eat the cuticle, but they prefer males, who have fewer toxins.
Q. Do monarchs in the north have a different chemical makeup because milkweed they eat is different from the southern milkweed?
A. Yes they do. Dr. Lincoln Brower and people working with him have used these differences to determine where adult butterflies they capture came from.
Q. What is the most abundant kind of milkweed in the U.S. and in Mexico?
A. This varies a lot in different areas. Where I live, common milkweed, or Asclepias syriaca is most abundant. Other species are more abudnant in other areas. For a nice description of many kinds of milkweed, you could look at the Monarch Watch homepage.
Q. Do bees sting monarch pupae?
A. No, but there are a few species of parasitic wasps that lay eggs in monarch larvae and pupae. (This isn’t really stinging them, but it looks like that’s what they’re doing). These eggs turn into wasp larvae that eat the monarch, then pupate and turn into new wasps.
Q. Do you have any concerns about rearing monarchs and diseases?
A. Yes. Monarchs can be infected with a protozoan parasite called Ophryocystis elektroscirrha. 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 could easily be contaminated. If they’re released into the wild, they could infect other monarchs. PLEASE read about this disease: Monarch Lab or Monarch Watch
Habitat and Distribution
Q. Where is the best place to find a monarch butterfly in the summer?
A. Anywhere that there are milkweed and flowers for nectar. I find it easier to find the larvae than the adults; just look at lots of milkweed plants. If you’d like to join a whole team of people all over the country who are trying to learn more about where monarchs live in the summer, you could participate in the: Monarch Larval Monitoring Project
Q. I know that the monarchs spend the winter in the mountains of Mexico, but why don’t they live in the Rocky Mountains in the summer?
A. Some do live in parts of the Rocky Mountains. However, at very high altitudes there is no milkweed. It is too cold for milkweed to grow, so monarchs couldn’t reproduce there. The monarchs need warm temperatures themselves in the summer - when it’s cold it takes them so long to develop from egg to adult that they wouldn’t have enough time to get through even one full generation.
Q. Do monarch butterflies live only in North America? If so, Why?
A. Monarchs also live in Australia, South America, Hawaii, and several other Pacific Islands. Most scientists think that they originated in the New World tropics (North and South American) and have spread to other places in the last few centuries. This spread was probably enabled by humans, who planted milkweed in new areas, and then may have moved the butterflies on purpose or by accident.
Q. Do monarchs live in other parts of the world besides Mexico and the USA?
A. Yes, monarchs are found in many places throughout the world, but they probably originated in the Americas, and were spread either with the help of humans or on their own to other places. They are found in Australia and New Zealand, and many islands east of these countries (most islands between Australia and Tahiti have monarchs). They are also found in Hawaii, most islands in the Caribbean, and even sometimes in western Europe.
Q. Are there different types of monarchs?
A. There are different subspecies of monarchs. Most of those found in South America are a different subspecies than the ones you see in North America. In islands in the Caribbean, both subspecies are sometimes found.
Q. Are there monarchs living on other continents?
A. Yes. I’ll copy the answer I gave above. Monarchs are found in many places throughout the world, but they probably originated in the Americas, and were spread either with the help of humans or on their own to other places. They are found in Australia and New Zealand, and many islands east of these countries (most islands between Australia and Tahiti have monarchs). They are also found in Hawaii, most islands in the Caribbean, and even sometimes in western Europe.
Q. In Mexico, would monarch butterflies survive when there is snow on the ground?
A. They can survive short periods of freezing temperatures, but not long periods. So a snowstorm wouldn’t necessarily kill them. It’s worse for them if they get very wet, and then freeze.
Q. Why do monarchs hang in trees?
A. The trees offer the monarchs protection from extreme temperatures, predators, and precipitation (rain and snow). Many people, particularly Alfonso Alonso, Lincoln Brower, Eneida Montesinos, and Eduardo Rendon, are studying how important the trees in the overwintering sites are to the monarchs. Eneida once said to me that she loves the monarchs, but she loves the forest even more, because without the forest there could be no monarchs. It is very clear that the trees are absolutely necessary to the survival of the monarchs.
Q. How many butterflies died in Mexico during the freeze and is this going to affect their population and future survival?
A. I answered the first question earlier. Any mortality affects their population somewhat, but animals that have such a high rate of reproduction can recover from short periods of high mortality. The key is short periods of high mortality - if this continued, it would affect their future survival. For example, if a hard winter is followed by a hard spring and summer, that would be very bad. So far, this spring is not looking very good for monarchs - it has been cold and dry in the Southern US, and there are not a lot of flowers or milkweed plants available. This could cause problems, but an excellent summer in the Northern US could allow the monarch population to bounce back. Year after year of high mortality in the overwintering sites would also be very bad.
Q. Are there any oyamel trees anywhere in the US?
A. Not that I know of, but there might be relict populations somewhere.
Q. What tree are they most similar to that can be compared to an oyamel tree in the US?
A. Oyamel firs are closely related to firs that do grow in the US, and look just about the same to me as the firs we have here.
Q. What kind of trees do they overwinter in, when they are in California?
A. If you’ve ever been to the coast of California, you’ll have noticed that most of the trees there are eucalyptus trees, and this is the main tree that the monarchs use. They also use pine trees where these are growing near the coast, and just about any other kind of tree that is growing in the right locations.
Behavioral Adaptations
Migration
Q. What tells the monarchs to migrate?
A. We’re not sure exactly what cues the monarchs use. We do know that those that migrate emerge in a state of “reproductive diapause,” which means that they won’t reproduce at four to six days of age like summer monarchs will. We also know that some combination of information from daylength, temperature, and possibly the age of the plants they are eating triggers this state.
Q. How are monarchs able to fly so far and know where to go?
A. This is a good question that I wish I could answer. We don’t know!!! Isn’t it nice that there are still a few mysteries in the world?!
Q. How long does it take a monarch to fly from Washington, DC to Angangueo, Mexico?
A. This would depend on temperature and wind conditions. On average, it probably takes about two months, total.
Q. Where do they store fat on their journey to Mexico and back?
A. In their abdomens.
Q. Why do they take the same route to Mexico and back?
A. We don’t know that they do! There are so many unanswered questions about monarch migration, that it will take many many scientists years to answer them all!
Q. How far do they fly in a day?
A. We can’t know for sure! However, we can learn from tagged individuals. One tagged monarch was recaptured 265 miles away from where it had been released the previous day! (This was the record flight from the Urquhart tagging program. The butterfly was tagged in Waterford, Pennsylvania and recaptured at a site in Virginia. )
Q. How do monarchs know where to go?
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 some information on this on the Monarch Lab Web site.
Q. When the monarchs go to Mexico how do they know where they are going?
A. This is a question that scientists are still working to answer. People working at the University of Kansas with Chip Taylor have shown that they use the sun, and also probably the earth’s magnetic field to know which way is south during the fall migration. But we don’t know how they find the specific spots in Mexico. Personally, I’m not sure that we’ll ever be able to answer this one - which I think is kind of nice. I like mysteries!
Q. How do they know their way back up north?
A. This isn’t completely understood yet. They may use the sun, or the earth’s magnetic field to tell them which way is north.
Q. Why do monarchs migrate and not hibernate?
A. This is an excellent question! For some reason, monarchs have just not evolved to hibernate. Iit’s a hard question to answer, because we need to know the evolutionary history of monarchs. We are quite sure that the ancestors of monarchs were tropical butterflies that could not survive long periods of very cold weather. When monarchs moved into areas that had cold winters, they never evolved the ability to tolerate these winters, and need to migrate to warmer locations.Many people think that monarchs evolved in the tropics, and just move north each spring to take advantage of all the milkweed we have in the summertime. Most other temperate insects can withstand the freezing temperatures of winter by entering a state called “diapause.” Some do this as eggs, others as larvae, pupae or adults.
Q: If monarchs did hibernate, how much food would they have to eat in order to survive the winter?
A: Since monarchs (and other insects) are cold-blooded, they do not use much energy when they are in a cool environment. Butterflies that hibernate don’t need to store as much fat as warm-blooded animals. Monarchs need more energy to migrate and overwinter than they’d need to overwinter in a cold climate. This means that it’s not energy considerations that make them leave, just an inability to withstand very cold temperatures.
Q. How do the monarch butterflies know that Arizona is a northerly direction?
A. Now this is a very interesting question. From my perspective, Arizona is in a southerly direction, and this is true for monarch butterflies in Minnesota too. If you are asking how do the butterflies know what is north, the answer is that this is not yet completely understood. They may use the location of the sun in the sky, or they may use the earth’s magnetic field.
Q. How many monarchs travel together at the same time?
A. The number of monarchs that travel together varies in different places and at different times. We aren’t sure if they actually seek each other out and fly together on purpose, or if they just happen to be together because they’re all going to the same place. In Minnesota, we often see one or a few traveling together. South of here, it is not uncommon to see dozens or even hundreds at a time (although we did see concentrations this big in Minnesota last fall).
Q. How do they travel such far distances?
A. They are able to travel such far distances by flying very efficiently. They take advantage of air currents and actually soar, like many birds do. This takes much less energy than flapping their wings all the time.They choose altitudes at which they can take advantage of the wind to help them on their long migratory flights. And they don’t fly when there’s a strong wind blowing in the wrong direction. They also store up a lot of energy for these long trips. This energy comes from the food they eat as caterpillars, and also from the nectar they get from flowers.
Q. Why didn’t the monarchs go to Arizona when they left Mexico rather than going to Texas?
A. We don’t know for sure why they go where they do. In fact, some may actually go to Arizona, and some people think that in some years monarchs from the overwintering colonies in Mexico may vear west and end up in the western population. However, if you look at map that shows mountain ranges, you will see that there are lots of mountains between the overwintering sites and Arizona. It would be very hard for the monarchs to fly over these mountains.
Q. Do monarchs get lost during migration?
A. We don’t know.
Q. Can butterflies travel over the ocean, and could butterflies land on water?
A. They do travel over the ocean - we know this because they are sometimes found on islands and oil rigs in the ocean. We don’t know if these butterflies are blown off course, or if they “mean to” fly over the ocean. It is likely that many monarchs that start over large bodies of water die, since they probably couldn’t survive after landing on water.
Q. Do monarchs have scent glands, and do they use scent markings to guide their migration North?
A. They do have scent glands, but it is unlikely (but possible, I guess) that they use these to guide their migration. If they marked plants on their way south, most of the leaves they’d marked wouldn’t be around the next spring! Maybe you could come up with a hypothesis for how this kind of scent marking would work.
Q. How far do monarchs travel in one generation?
A. It depends on the generation. The ones that emerge in the late summer and fall in the northern US will travel all the way to their overwintering sites in Mexico, and then about half way back in the spring. How far is this (measure it on a map)? Other generations don’t travel so far. Why?
