The annual migration of North America’s monarch butterfly is a unique and amazing phenomenon. The monarch is the only butterfly known to make a two-way migration as birds do. Unlike other butterflies that can overwinter as larvae, pupae, or even as adults in some species, monarchs cannot survive the cold winters of northern climates. Using environmental cues, the monarchs know when it is time to travel south for the winter. Monarchs use a combination of air currents and thermals to travel long distances. Some fly as far as 3,000 miles to reach their winter home! Monarchs can travel between 50-100 miles a day; it can take up to two months to complete their journey. The farthest ranging monarch butterfly recorded traveled 265 miles in one day.
Monarchs roost for the winter in oyamel fir forests at an elevation of 2,400 to 3,600 meters (nearly 2 miles above sea level). The mountain hillsides of oyamel forest provide an ideal microclimate for the butterflies. Here temperatures range from 0 to 15 degrees Celsius. If the temperature is lower, the monarchs will be forced to use their fat reserves. The humidity in the oyamel forest assures the monarchs won’t dry out allowing them to conserve their energy.
Researchers are still investigating what directional aids monarchs use to find their overwintering location. It appears to be a combination of directional aids such as the magnetic pull of the earth and the position of the sun among others, not one in particular. It is truly amazing that these monarchs know the way to the overwintering sites even though this migrating generation has never before been to Mexico!
Clustering in Colonies
Monarchs cluster together to stay warm. Tens of thousands of monarchs can cluster on a single tree. Although monarchs alone weigh less than a gram, tens of thousands of them weigh a lot. Oyamel trees are generally able to support the clustering butterflies.
Monarch butterflies perform annual migrations, which have been called one of the most spectacular natural phenomena in the world. Starting in September and October, eastern and northeastern populations migrate from southern Canada and the United States to overwintering sites in central Mexico where they arrive around November. They start the return trip in March, arriving around July. No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least four generations are involved in the annual cycle.
The ideal habitat for monarchs in winter exists in their overwintering sites. The factors influencing the habitat include: the condition of the forest canopy, precipitation, predation, availability of suitable trees on which to roost, sources of water, the ideal temperature range, sunlight, lack of rain and ice and human activity near the sites. If conditions are too hot in the overwintering sites, the butterflies will use up their fat reserves and not survive until spring. High temperatures initiate reproductive behavior with the possibility of the butterflies leaving the overwintering areas too early, while it is still too cold in the north to stimulate the emergence of food plants and nectar plants.
The Canadian researchers Fred and Nora Urquhart investigated the phenomenon from 1940, culminating in the discovery of the hibernation sites in central Mexico in 1975. They designed the tiny labels that adhere to the butterflies and recruited thousands of volunteers to map the migration.
The Monarch Butterfly Biosphere Reserve (Spanish: Reserva de Biosfera de la Mariposa Monarca) is a World Heritage Site containing most of the over-wintering sites of the eastern population of the monarch butterfly. The reserve is located in the Trans-Mexican Volcanic Belt pine-oak forests ecoregion on the border of the State of Michoacán and State of México. Millions of butterflies arrive in the reserve annually. Butterflies only inhabit a fraction of the 56000 hectares of the reserve from October–March. The biosphere’s mission is to protect the butterfly species and its habitat.
The reserve was designated in 1980 by President José López Portillo. It was at this time assigned the category of “special biosphere reserve.” In 1986, the area and boundaries were defined. In 2000, it received its current name (Reserva de la Biosfera Mariposa Monarca). UNESCO declared the biosphere a World Heritage site in 2008, as a Natural Asset.
Generation 1 monarchs are the offspring of the monarchs who overwintered in Mexico. Each successive generation travels farther north. It will take 3-4 generations to reach the northern United States and Canada.
Monarch butterflies go through four stages during one life cycle, and through four generations in one year. The four stages of the monarch butterfly life cycle are egg, larvae (caterpillar), pupa (chrysalis), and adult butterfly. The fourth generation of monarch butterflies is a little bit different than the first three generations. The fourth generation is born in September and October and goes through exactly the same process as the first, second and third generations except for one part. The fourth generation of monarch butterflies does not die after two to six weeks. Instead, this generation of monarch butterflies migrates to warmer climates like Mexico and California and will live for six to eight months until it is time to start the whole process over again.
Note: In effect, the fourth generation of the Monarch butterflies are the only ones that migrate, as, sadly, the butterflies of the first three generations hardly survive beyond 6 weeks of emerging from their pupas. This generation is known as “Methusela” generation, because of its longevity.
Sexual differences: Sexual dimorphism exists in some species, i.e., males and females are different. These differences can be in form, function or behavior. Monarch butterfly males have two small black areas on the posterior wings and their venation is thinner than that of the females.
Feeding: the milkweeds are the main food of Monarch butterfly caterpillars. These plants produce toxic substances that reduce the voracity of their predators. However, Monarch caterpillars assimilate these substances and store them in their skin, in turn making themselves toxic and thus protected from a great number of predators. The adult butterflies also feed on the nectar of the milkweeds.
Experiences with Aztec Explorers
- Video by Aztec Explorers: https://www.youtube.com/watch?v=yfFJrhX_IU8
- Blog about Aztec Explorers / Peter Winckers / Lidia Herrera + the Monarch butterflies by True Ink:
- Blog about Aztec Explorers + the Monarch butterflies by La Mariposa Vagabunda:
Let´s explore the sanctuaries together with Aztec Explorers!
Our 2 most favorite sanctuaries, after organizing more than 8 years Monarch butterfly trips, are El Rosario in the State of Michoacan (at 3.5 to 4 hours distance from Mexico City) and Piedra Herrada in the State of México (at 2.5 hours distance from Mexico City). Both sanctuaries and all months (between mid November and mid March) can give the best experiences, the most important is the weather; ideally we have a cloudless, sunny day for a lot of butterfly activity (on a cloudy, rainy day they stay together high up their branches, also impressive but it’s nicer to see them all fly around). And both / all sanctuaries need a steep hike uphill of 1.5 to 2.5 hours to reach the colonies, at about 3200 to 3400 meters (the location of the colony can change overnight, depending on the weather conditions; there are horses available for around 200 pesos if necesary).
Below our group trips planned for December, January, February and March (but we can organize private trips, also to other sanctuaries, at any other dates; from Mexico City, but also from other cities like Toluca, Queretarro and Puebla. Ask us for a quote!).
Option 1: Piedra Herrada and Valle de Bravo
Visit the sanctuary of Piedra Herrada, at 2.5 hours distance of Mexico City and 40 minutes from Valle de Bravo, and the beautiful town and lake of Valle de Bravo (on of the 121 traditional Pueblos Mágicos of Mexico). Price 850 Mexican pesos, includes private transport for our small group, entrance, bilingual coordinator and local guide. This trip also includes a boat trip on the lake of Valle de Bravo. Reservations and payment information: + 52 1 55 1308 3732 (Whatsapp).
Dates Piedra Herrada and Valle de Bravo:
November 17 + 23
December 1, 7, 15, 21, 29
January 4, 12, 18, 26
February: 9, 15, 23, 29
March: 8, 14
Note: also possible as a private trip from Mexico City, ask us for a quote on +52 1 55 1308 3732 (Whatsapp)
Option 2: EL Rosario
Visit the sanctuary of El Rosario, at 3.5 to 4 hours distance of Mexico City. Price 850 Mexican pesos, includes private transport for our small group, entrance, bilingual coordinator and local guide. Reservations and payment information: + 52 1 55 1308 3732 (Whatsapp).
November 16, 17, 24, 30
December 8, 14, 22, 28, 30
January 5, 11, 19, 25
February: 2, 8, 16, 22
March: 1, 7, 15