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Frequently Asked Questions

21. When do the Monarchs mate and how does this affect their flight?
The Monarchs that migrate to Mexico don't mate before they leave the north, but most females do mate before they leave the colonies to come north in the spring. How mating affects their flight isn't known. During mating, males transfer more material than just sperm to females - the sperm are packaged in a bundle called a spermatophore that can weigh up to 10%, but usually about 5%, of the female's total weight. This added weight might be hard to carry, but since the spermatophore is broken down and assimilated by the female it also provides her with energy. This question needs more study. [Back to FAQs]

22. How do humans influence Monarchs?
Unfortunately, much of our influence is bad. We spray insecticides that kill Monarchs along with pest insects and use herbicides and mowers that kill the milkweed plants the larvae feed on. We destroy prairies which have lots of good flowers for nectaring and larval foodplants. We have destroyed Monarch overwintering sites; in California, houses, parking lots, and shopping centers have been built on Monarch overwintering locations. We might even be changing the climate in ways that will hurt Monarchs and other butterflies. This is pretty depressing, but if we understand the impact we have on Monarchs, and other species, and if we chose to care about these organisms, we can minimize the negative impacts of human activity on this and other species. Conservation is one of the goals of the Monarch Watch and it is our intention to study human impacts on Monarch populations and to promote activities and policies that will ensure the continuation of Monarch migrations. [Back to FAQs]

23. Besides milkweed, what do Monarchs eat?
The larvae only eat plants in the milkweed family (Asclepiadaceae). There are 106 species of milkweeds in North America. Many of these species have become uncommon and some rare and endangered (Asclepias meadii) due to destruction of habitats. For more information on milkweeds see the "Milkweed Handbook" section of the home page. The adult Monarchs obtain nectar from flowers. Nectars in butterfly flowers typically contain 15% or less dissolved sugars, trace amounts of vitamins and minerals and in some cases small quantities of amino acids. Monarchs in captivity can be feed dilute sugar or honey water, diluted fruit juices and slices of fresh watermelon. For more information on the care and feeding of Monarchs see the section on "How to raise Monarchs" [Back to FAQs]

24. Does the presence of flowers affect Monarch migration?
Monarchs need the carbohydrates (sugars) in nectar to provide energy for day to day activities and to fuel the long migrations to and from Mexico. It is logical to assume that the quality and quantity of nectars available from various flower species along the way could have a significant impact on the Monarch population. An early freeze or a severe drought that reduces the nectar or kills flowers could have a devastating effect on the migration. However, the importance of nectar to the migration has not been studied. Rainfall and soil moisture are two of the important factors that determine the ability of plants to secrete nectar and it is possible that some of the year to year variation seen in the concentrations of Monarchs during the fall migration are due to patterns of rainfall that influence the amount of flowering and nectar secretion along the migration pathways. [Back to FAQs]

25. Does pollution affect Monarch migration?
We don't know. Ozone pollution has a distinct negative effect on milkweed plants and its possible that milkweeds, like other plants, pick up lead from car exhaust when they grow adjacent to well traveled roadways. The effects of lead and other airborne contaminants on Monarch survival are unknown. [Back to FAQs]

26. Do the same number of butterflies come back each year?
There seems to be quite a bit of variation in the numbers of butterflies that leave for Mexico each fall or return from there each spring. One of the objectives of the Monarch Watch is to correlate the data from the tagging program and observations of the migration, in combination with weather pattern data, to both short and long term changes in the size of the Monarch population. This is a long term study and such studies are needed to assess population trends and to develop a plan for the continued preservation of the Monarch migration. [Back to FAQs]

27. If water gets on a monarch's wings, does their color come off?
Monarchs are very good at shedding water. Rain water and mist will bead up on the wings and the water will simply fall off with the wings remaining dry. Occasionally, if Monarchs are in contact with standing water, the wings will loose their water-shedding ability and they will get wet. When this happens, the wings often become discolored but the pigments are usually not bleached out. [Back to FAQs]

28. What did Monarch butterflies evolve from?
Fossil moths, identified from imprints of wings, in shale and limestone deposits, date back to about 208 million years ago (early Jurassic). Butterfly fossils have been found in deposits which have been dated as 48 million years old (middle Eocene). Because butterflies have many advanced characteristics, they are thought to have evolved from moths. The fossil beds in The Florissant Fossil Beds National Monument in Colorado have produced 12 species of fossil butterflies. These fossils are thought to be 35 million years old and two species, Chlorippe wilmattae and Vanessa amerindica are so similar to modern butterflies in pattern and wing shape that they have been classified as belonging to modern genera. In fact, Vanessa amerindica is similar to the Old World Painted Lady (Vanessa indica) to the Painted Lady (Vanessa cardui) which is common in North America, Europe and northern Africa. Monarchs and other milkweed butterflies are not represented in the fossil record, so we can't be certain when they evolved, but they are part of a large family called Nymphalidae and this group was one of the earliest to appear in the fossil record. [Back to FAQs]

29. Why don't the Monarch butterflies fly at night?
Butterflies are diurnal insects which means they only fly during the day. We are not aware of any butterflies that fly at night. Why this is the case is not clear but butterflies are generally brightly colored and highly visual and their eyes are not designed to function under low light conditions. Moths are predominantly nocturnal (night flying) and they have what are known as "dark adapted" eyes which allow them to fly at night when light levels are extremely low. Moths are usually drab in coloration but some species are active in the daytime and curiously most of these species are brightly colored and relatively distasteful to predators. What about their eyes, are they light or dark adapted or both? Hmmm! Don't know the answer to this one and I'm not sure this has been studied. [Back to FAQs]

30. Are Monarchs the only butterflies that migrate?
No, actually many butterflies migrate. In fact, many of the common butterflies you are familiar with such as Painted Ladies, Red Admirals and Question Marks migrate northward each spring. Return migrations (southerly) in the fall are not well documented for these species. On a world wide basis, only Monarchs migrate to a specific overwintering site year after year. [Back to FAQs]

31. How do Monarchs know when to migrate?
We don't know for sure, but decreasing daylength and temperature probably provide cues. We do know that Monarchs begin to migrate when daylength begins to decline (3 min/day) in late August in the northern states and Canada. The temperatures are also decreasing at this time and the quality of the late season foodplants is changing as well. One, or perhaps an interaction of two or all, of these factors leads to the development of "reproductive diapause", a condition in which reproduction is suppressed; ovaries in females and seminal vesicles in males are undeveloped. Carbohydrates taken up in nectar are used for maintenance but are also converted to lipids which are stored in an extensive fatbody in the abdomen in Monarchs that are in diapause. Diapause is difficult to "break" in most insects. However, in Monarchs, migrant butterflies can easily be induced to become reproductive by increasing the photoperiod to 14 hrs and raising the temperature to 75-80. The conversion from diapause to females that are fully reproductive, as indicated by egg laying, can be is as little as 6 days. On the other hand, it seems to be difficult to induce diapause and there are no published accounts of the exact conditions required to produce migratory/diapausing butterflies. [Back to FAQs]

32. Can Monarchs fly when it rains?
No. Heavy rainfall could drive Monarchs to the ground where they would be unprotected. Just before rains begin (how do they know?), Monarchs seek shelter under overhanging vegetation. At these sites they position themselves vertically, with wings closed. In this position , even if rainfall hits them, the water runs off to the ground. [Back to FAQs]

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