Biological Sciences, Santa Barbara City College pipeline center for sustainability

Biology 130: Methods in Field Biology

Field Technique:  Monarch Butterfly Tagging

Data Sheets Jan 27, 2017

monarch tagging



Monarch Butterfly Congregation
(Clump of Monarchs, Ellwood Grove, Santa Barbara, CA. Photo by Adam Green)

Useful Websites: (NPR story and photos)

Monarch Life Cycle:

All insects change in form as they grow; this process is called metamorphosis. There are two kinds of metamorphosis, incomplete (or simple) metamorphosis, and complete metamorphosis. An example of incomplete metamorphosis is found in grasshoppers. The young nymphs usually look much like small wingless adults. The wings develop externally, and there is no prolonged immobile (pupal) stage. Butterflies and moths undergo complete metamorphosis, in which there are four distinct stages: egg, larva (caterpillar), pupa, and adult. Monarch development from egg to adult is completed in about 30 days.

Egg (3-4 days)

Monarchs usually lay a single egg on a plant, often on the bottom of a leaf near the top of the plant. It is difficult to tell just how many eggs each female lays during her life, but the average is probably from 100 to 300. The eggs hatch about four days after they are laid.

Monarch egg
Approximate dimensions: 1.2mm high; 0.9mm wide

Larva (Caterpillar; 10-14 days)

It is during this stage that Monarchs do all of their growing. They begin life by eating their eggshell, and then move on to the plant on which they were laid.

Monarch Larvae

When the caterpillar has become too large for its skin, it molts, or sheds its skin. At first, the new skin is very soft, and provides little support or protection. The new skin soon hardens and molds itself to the caterpillar, which often eats the shed skin before starting in anew on plant food! The intervals between molts are called instars. Monarchs go through five instars. Approximate length of body at each stage: 1st instar, 2-6mm; 2nd instar, 6-9mm; 3rd instar, 10-14mm; 4th instar, 13-25mm; 5th instar, 25-45mm.

Pupa (Chrysalis; 10-14 days)

During the pupal stage the transformation from larva to adult is completed. Pupae are much less mobile than larvae or adults, but they often exhibit sudden movements if they are disturbed. Like other butterflies, Monarch pupae are well-camouflaged, since they have no other means of defense against predators.

Monarch Pupa


The primary job of the adult stage is to reproduce - to mate and lay the eggs that will become the next generation.

Females begin laying eggs right after their first mating, and both sexes will mate several times during their lives. Adults in summer generations live from two to five weeks. Each year, the final generation of Monarchs, which emerges in late summer and early fall, has an additional job: to migrate to their overwintering grounds, either in central Mexico for eastern Monarchs or in California for western Monarchs. Here they survive the long winter until conditions in the United States allow them to return to reproduce. These adults can live up to eight or nine months.

Monarch adults
(Adult Monarchs in clump. Photo by Adam Green)

Male and female Monarchs can be distinguished easily. Males have a black spot on a vein on each hind wing that is not present on the female. These spots are made of specialized scales which produce a chemical used during courtship in many species of butterflies and moths, although such a chemical does not seem to be important in Monarch courtship. The ends of the abdomens are also different in males and females, and females often look darker than males and have wider veins on their wings.

male monarch
(This image shows the specialized group of black cells on the hind wing of males. Photo by Adam Green)

No growth occurs in the adult stage, but Monarchs need to obtain nourishment to maintain their body and fuel it for flight. Nectar from flowers, which is about 20% sugar, provides most of their adult food. Monarchs are not very picky about the source of their nectar, and will visit many different flowers. They use their vision to find flowers, but once they land on a potential food source, they use taste receptors on their feet to find the nectar.

monarch feeding
(In this image you can see the long probiscis used to drink nectar from flowers and the complex feet that have tase receptors. Photo by Adam Green)


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.

Monarch migration

Some other species of Lepidoptera (butterflies and moths) travel long distances, but they generally go in one direction only, often following food. This one-way movement is properly called emigration. In tropical lands, butterflies do migrate back and forth as the seasons change. At the beginning of the dry season, the food plants shrivel and the butterflies leave to find a moister climate. When the rains arrive, the food plants grow back and the butterflies return.

When the late summer and early fall Monarchs emerge from their pupae, or chrysalides, they are biologically and behaviorally different from those emerging in the summer. The shorter days and cooler air of late summer trigger changes. In Minnesota this occurs around the end of August. Even though these butterflies look like summer adults, they won't mate or lay eggs until the following spring. Instead, their small bodies prepare for a strenuous flight. Otherwise solitary animals, they often cluster at night while moving ever southward. If they linger too long, they won't be able to make the journey; because they are cold-blooded, they are unable to fly in cold weather.

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-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.

We have many congegation sites in the Santa Barbara area. Two that are readily accessible and often have many Monarchs are found on Ellwood Mesa.



Monarch Population counts
(Monroe, M., C. Fallon, D. Frey, and S. Stevens. 2015. Western Monarch Thanksgiving Count Data from 1997–2014. Available at:


ellwood grove butterfly population over time


From the above graph of the Monarch population at our local grove at Ellwood Mesa you can see the fluctuation in population size. This may be the result of weather and other causes or mortality or possibly movement among groves. I have not seen any study that actually tracks possible movement among groves in our area so I do not know if that happens and if so, how commonly.

The Western Monarch Thanksgiving Count is a yearly effort of volunteer citizen scientists to collect data on the status of monarch populations overwintering along the California coast. Thanks to the extraordinary efforts of these volunteers, we have over 15 years’ worth of data demonstrating that monarchs have undergone a dramatic decline in the western U.S.

Estimating the numbers of overwintering butterflies is the best way to gauge the status of the monarch population. Scientists believe loss and degradation of both breeding and overwintering habitat, pesticide use, and drought—exacerbated by climate change—may all be contributing to the decline in monarch numbers.

Deforestation in Monarch Reserve Mexico:

Each year millions of monarch butterflies migrate thousands of miles back and forth from wintering grounds in Mexico to their breeding locations in the eastern United States and Canada. In the fall, the monarchs return to just 12 forested mountaintops in central Mexico, where they form colonies in which millions of butterflies cluster on the trunks and branches of the trees. Despite the creation of protected areas and reserves, illegal logging has been steadily shrinking this unique, critical monarch habitat.


deforestation monarch grove mexico

Recently, scientists identified severe degradation of the forest habitat within the Monarch Butterfly Biosphere Reserve in central Mexico using imagery from the commercial Ikonos satellite. The white line indicates the boundaries of the reserve’s “Core Zone,” where logging is forbidden according to the Presidential decree that established the reserve in November 2000. This pair of images shows the affected area on March 22, 2004 (top) and February 23, 2008 (bottom). The degraded area is the site of the Lomas de Aparicio monarch colony. The circles on the image (not to scale) indicate the approximate positions of the colony in different seasons. Colonies typically cover areas of 0.25–2.0 hectares (equivalent to a circle with a diameter of 60–160 meters, or 200–525 feet). The area had been largely intact since at least 1986. Overwintering colonies have been documented there since 1996, but have probably formed there long into the past.

In the 2004 image, the beginnings of the logging operation are apparent in an area to the east of (and partially inside) the core zone. Based upon this pair of images, and a similar image taken in 2006 by the QuickBird satellite, scientists Lincoln Brower, Daniel Slayback, and Isabel Ramirez have determined that approximately 450 hectares (1,110 acres) of forest were logged between 2004 and 2008, representing 3.3% of the 13,552 hectares (33,410 acres) core zone of the reserve. The majority of this logging (290 hectares, or 717 acres) has occurred since March 2006.

Forest degradation—which progresses from thinning to clear-cutting—has been an ongoing problem throughout the reserve. Other logging incursions have destroyed several other prime overwintering areas within the reserve, making them unsuitable for monarch colonies. Based upon the degradation apparent in these images, it is unlikely monarchs will form overwintering colonies at this Lomas de Aparicio site in future years. If they do return, they will be subject to much greater environmental risks during their six-month overwintering stay. An intact forest canopy serves a critical role by protecting the monarchs from both freezing cold during winter storms and from excessive warmth during the days. If unprotected from the sun, monarchs dehydrate and also risk starvation: they burn substantially more of their fat reserves when they can’t keep cool.


The researchers are greatly concerned that the entire monarch butterfly migration and overwintering phenomenon in eastern North America may collapse in the near future if the Mexican government does not fully enforce the logging ban.


  • Brower, L. P., Castilleja, G., Peralta, A., Lopez-Garcia, J., Bojorquez-Tapia, L., Diaz, S., Melgarejo, D., and Missrie, M. (2002). Quantitative changes in forest quality in a principal overwintering area of the monarch butterfly in Mexico: 1971 to 1999. Conservation Biology,16, 346-359.
  • Missrie, M. (2004). Design and implementation of a new protected area for overwintering monarch butterflies in Mexico. In K. S. Oberhauser and M. J. Solensky, (Eds.) The Monarch Butterfly Biology and Conservation (pp.141-150). Ithaca: Cornell University Press.
  • Ramirez, M. I. R., and Zubieta, R.H. (2005). Analyses regional y comparison ecologica del cambio en la cubierta forestal in la Reserva de la Biosfera Mariposa Monarca. World Wildlife Fund-Mexico. Accessed March 6, 2008.
  • Ramirez, M., Miranda, G., and Zubieta, R. (2006). Serie Cartografica Monarca Volumen 1. Vegetacion y Cubiertas del Suelo, 2006. Reserva de la Biosfera Mariposa Monarca, Mexico. Mexico City: Instituto de Geografia, UNAM.
  • Slayback, D., Brower, L., Ramirez, M., and Fink, L. (2007). Establishing the presence and absence of overwintering colonies of the Monarch butterfly in Mexico by the use of small aircraft. American Entomologist, 53, 28-40.

The challenge of protecting a species like the Monarch is the numerous potential threats along the long migration route:

Further reading


The following film can give you a feel for the Monarch and its migration that you really can't get by just observing one overwintering site. This film centers on the larger population on the east side of the Rockies, so it is different from our Western population. It also goes into how they developed techniques to study the migration. It costs $2.99 to watch it on Youtube, but I think you will find it worthwhile.



monarc tagging

Placing tags on Monarchs allows us to piece together their movements throughout the year.


monarch tagging

The tags are simply small stickers that can be placed on the underside of the hind wing. This way, when the butterfly is resting with its wings folded up the tag can be seen and read.


wing measure

While the butterflies are in hand we can also collect data on size (wing length).


wing measure

Wing length is measured from the tip of the wing to the notch where the wing meats the thorax.


parasite sampling

We will also collect cells from the abdomen using a small clear sticker. These are then sent to a lab in Georgia where they determine if the butterfly was infected with a parasite.


parasite measure

We will also record whether they are male or female. Male butterflies have protrusions from the end of their abdomen that clasp the females during mating.


monarch male


You an see in the image below the difference between female (left) and male (right). By palpating the abdomen of the females we can also determine if they are pregnant (contain a spermatophore). It feels like a small BB in the abdomen.

male and female monarch


All data are entered on a data sheet:


data sheet


tagged monarch

The above image was taken using a cell phone thrugh a scope. You can read the tag including the individual identifying number and the phone number to call to report it. This butterfly was tagged in elgin, Arizona and flew nearly 700 miles north-west to Ellwood mesa in Goleta. Out of the nearly 5,000 butterflies at Ellwood mesa's Sandpiper congregation, this was the only one tagged. Repeated efforts over years provide the data that eventually pieces together the migration routes of these amazing butterflies.


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