Monarch Butterflies…

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“Unlike most other insects in temperate climates, Monarch butterflies cannot survive a long cold winter. Instead, they spend the winter in roosting spots. Monarchs west of the Rocky Mountains travel to small groves of trees along the California coast. Those east of the Rocky Mountains fly farther south to the forests high in the mountains of Mexico. The monarch's migration is driven by seasonal changes. Daylength and temperature changes influence the movement of the Monarch.

“In all the world, no butterflies migrate like the Monarchs of North America. They travel much farther than all other tropical butterflies, up to three thousand miles. They are the only butterflies to make such a long, two way migration every year. Amazingly, they fly in masses to the same winter roosts, often to the exact same trees. Their migration is more the type we expect from birds or whales. However, unlike birds and whales, individuals only make the round-trip once. It is their children's grandchildren that return south the following fall.

“Fat, stored in the abdomen, is a critical element of their survival for the winter. This fat not only fuels their flight of one to three thousand miles, but must last until the next spring when they begin the flight back north. As they migrate southwards, Monarchs stop to nectar, and they actually gain weight during the trip! Some researchers think that Monarchs conserve their "fuel" in flight by gliding on air currents as they travel south. This is an area of great interest for researchers; there are many unanswered questions about how these small organisms are able to travel so far.

“Another unsolved mystery is how Monarchs find the overwintering sites each year. Somehow they know their way, even though the butterflies returning to Mexico or California each fall are the great-great-grandchildren of the butterflies that left the previous spring. No one knows exactly how their homing system works; it is another of the many unanswered questions in the butterfly world.

 “As winter ends and the days grow longer, the Monarchs become more active, beginning to mate and often moving to locations lower on the mountainsides. They leave their Mexican roosts during the second week of March, flying north and east looking for milkweed plants on which to lay their eggs. These Monarchs have already survived a long southward flight in the fall and winter's cold; they have escaped predatory birds and other hazards along the way, and are the only Monarchs left that can produce a new generation. If they return too early, before the milkweed is up in the spring, they will not be able to lay their eggs and continue the cycle.

"The migrating females lay eggs on the milkweed plants they find as they fly, recolonizing the southern United States before they die. Soon the first spring caterpillars hatch and metamorphose into orange and black adults. It is these newly emerged Monarchs, the offspring of the butterflies that made the fall journey, that recolonize their parents' original homes. Summer Monarchs live a much briefer life than the overwintering generation; their adult lifespan is only three to five weeks compared with eight or nine months for the overwintering adults. Over the summer there are three or four generations of Monarch butterflies, depending on the length of the growing season. Since each female lays hundreds of eggs, the total number of Monarch butterflies increases throughout the summer. Before the summer ends, there are once again millions of Monarchs all over the U.S. and southern Canada.

“There are two geographically distinct Monarch populations in North America. The eastern population overwinters in Mexico and breeds east of the Rocky Mountains. The western population overwinters along the California coast and breeds in areas west of the Rockies. Contact between eastern and western Monarchs is minimal suggesting that there is little exchange, or what scientists call gene flow, between these populations.

“How much does a Monarch weigh?
Monarchs range in mass from .25 to .75 grams (a dime has a mass of 2.3 grams).

“How fast does the migration advance?
the migration advances at roughly 50 miles (75 km) per day (1500/30 migrating days from 28 Aug. to 28 Sept.). However, these are averages, and there are reports from recoveries of tagged Monarchs which indicate flight distances up to 129 km a day.

“How fast do individual migrating Monarchs fly?
Their flight speeds have been measured at 5 meters per second,18 km or 12 miles per hour; but, if disturbed, they can fly much faster for short distances.

“Do Monarchs occur outside of North America?
Yes. Monarchs are found at middle elevations in many places in central and south America. In the last century Monarchs were introduced, evidently by ship traffic, to the Azores, Australia, New Zealand, Hawaii and many Pacific islands. More recently a limited population of Monarchs has become established in southern Spain.

“How long do adult Monarchs live?
In captivity, reproductively active Monarchs can live up to 6 weeks - if they are well cared for. In the wild, the duration of the life span depends on the time of year. Summer Monarchs, which are reproductively active, probably live 2-6 weeks. The survivorship of summer Monarchs probably declines when nectar is scarce and when temperatures exceed 95 F (35 C). Generally insects live "faster" and have shorter lifespans when it is hot and dry. Monarchs which overwinter in Mexico can live up to 8 months! These Monarchs are in diapause and are not reproductively active until the end of the winter in Mexico. The cool conditions at the roost sites in Mexico, the inactivity of the butterflies and the lower metabolism during diapause, contribute to the longer lifespan of the migratory generation.

“Do Monarchs that migrate to Mexico in the fall make the trip back to the area from which they started?
After clustering in the roosts in Mexico for 5 months in the winter, Monarchs begin to make their way back north. Before leaving the roosts, they become sexually active and mate multiple times. As the female Monarchs move northward, they lay eggs on milkweed plants along their flightway. Most of the northward migrants complete their reproduction in the southern states, but each spring relatively small numbers return to the Midwest, sometimes as far north as southern Iowa. However, very few if any, reach the area from which they originated. It is generally believed that Monarchs maturing from the first eggs laid on milkweeds in the southern states in late March and early April continue the migration northward in May, eventually reaching the northern limits of the breeding grounds in central and eastern Canada. After 2-3 summer generations, Monarchs will again migrate to their winter roosts in the fall without having any previous experience with locating the roosts or "knowing" where the roosts are. How do they do this?! This is one of the mysteries of the Monarchs.

“Where did the Monarch get its name?
Early settlers who came to North America from Europe, particularily those from Holland and England, were impressed by the sight of the Monarch butterfly. So, they named it "Monarch," after King William, Prince of Orange, stateholder of Holland, and later named King of England. The monarchs' color suggested the name.

“What do adult butterflies and moths eat?
Most butterflies use their proboscis (tongue) to obtain nectar from flowers. Some species obtain juices, salts and moisture from rotting fruit, mud, dung, and even dead animals, and in the American tropics there is one group, the longwings (Heliconius), that collects and digests pollen.

“How do Monarch butterflies breathe?
When we breathe, oxygen goes into our lungs and is picked up by blood which carries it to cells throughout our body. Because we are relatively large, we need this complicated system. But insects are so small that tiny air tubes (called tracheae) carry air from the outside directly to body tissues. Air enters and leaves these tubes through small holes (called spiracles) on the outside of the thorax and abdomen. Spiracles are easily seen on larvae and pupae but are difficult to see on adults because they are obscured by scales.

“Why do Monarch butterflies all have the same design on their wings?
The design or pattern on the monarch's wings is genetically programed. This means that the pattern is determined by genetic rather than environmental factors. The color of our eyes and hair is genetically determined but our height and weight are partly determined by environmental factors such as the amount and quality of food we eat. The pattern on the wings of Monarchs is not influenced by the temperatures during larval and pupal development, nor the food plants upon which the larvae feed, however, the size of the adult butterflies is related to the quantity and quality of the leaves the larvae have fed on.

“Why do Monarchs have this particular design on their wings?
Colors and patterns of insects are thought to be the result of interactions of each species with their environment. Bright and/or contrasting colors, such as the black and orange of the Monarchs wings, warn predators that the insects are distasteful (Monarchs are distasteful to many predators due to the chemicals, cardenoloids, they acquire from feeding on milkweeds) and, in some cases, dangerous (certain caterpillars with urticating hairs).  In addition to communication within and between species, colors and black (melanic) pigment can also serve to maximize and minimize heat gain due to adsorption of infrared energy from sunlight. Insects tend to be more melanic and "hairier" in mountainous areas and far northern latitudes, where temperatures are low. Black pigments, particularly at the base of the wings, have been shown to enhance convective heat gain from the sun. Tropical species which frequent open, sunny habitats tend to be light in color while those which reside within the forest are usually darker. Within forests, darker colors can help conceal the insects from predators but some species also appear to use these colors to adsorb heat since they are often seen to "sun" themselves in patches of sunlight when temperatures are low.

“Why do butterflies have to be in a chrysalis before they are born?
Butterflies and moths have complete metamorposis, which means they have four separate life stages: egg, larva (or caterpillar), pupa (or chrysalis in butterflies), and adult. The pupa is a special stage during which the tissues of the larva become reorganized and transformed into those of the adult butterfly. The changes from larva to adult are so extensive that they appear to require this intermediate or resting stage.

“Why do Monarch butterflies rest in groups on branches during the migration and while they are at the roost sites in Mexico?
The advantages of clustering behavior by migrating and overwintering Monarchs are not well understood. There are several possible explanations. Clustering could simply be an artifact of too many butterflies having a preference for the same type of resting spot. Or, perhaps, it's a follow-the-leader type of behavior in which some butterflies find a good spot and others join them. Temperature and predation may also influence clustering. This past fall ('95) we observed that clusters which formed late in the day appeared to be tighter on evenings with cooler temperatures. Why? Once Monarchs are on the roosts, and have cooled to ambient temperature, no heat is generated by the cluster. So, what are the advantages of such tight clusters? Is heat gain from the sun or from "shivering" the next morning greater in clusters? And, are tightly clustered Monarchs therefore able to become active earlier in the day than those Monarchs which are isolated? What about predation? Is there a "startle effect" and an improved chance of escape if predators attack a large cluster rather than a small one? Clustering could have several advantages but so far there are no studies of this behavior. This is an example of the many unanswered questions we have about insect behavior.

“How high can a Monarch fly?
Monarchs have been reported by glider pilots at 1250 meters (4062 feet - that's about 3/4 of a mile above the earth's surface!). And, commercial and military pilots have seen Monarchs at 3000-4000 meters over midwestern states in September. How do they get this high? They probably take advantage of bubbles (or columns) of warm air (thermals) just as birds do (e.g. hawks, eagles, vultures). If you watch migrating Monarchs in the fall, you can often see them shift from directional flight to one in which they circle, usually with the wings set in a fixed position. With each circle they rise and soar in a pattern which we usually associate with hawks.. At the top of the bubble or thermal they resume their directional flight. This behavior is most easily observed in the morning when wind speeds are low. Winds tend to break up the weaker thermals and displace the butterflies so the Monarchs probably only reach high altitudes under very special conditions.

“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.

“Besides milkweed, what do Monarchs eat?
The larvae only eat plants in the milkweed family (Asclepiadaceae).  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

“Why don't the Monarch butterflies fly at night?
Butterflies are diurnal insects which means they only fly during the day.    …their eyes are not designed to function under low light conditions.

“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.

(All the above information and maps came from www.MonarchWatch.org.)