Tagging Monarch Butterflies Helps Track Their Migration
By Kevin Fitzgerald
Every autumn, the Migration Festival takes place at Lighthouse Point on the seacoast of Connecticut near New Haven. It’s a celebration of flying creatures: birds, butterflies, and dragonflies. This event is a cooperative effort sponsored by the New Haven Parks, Recreation, and Tree Department; New Haven Bird Club; Audubon Connecticut; Menunkatuck Audubon Society; Connecticut Audubon Society; New England Hawkwatch; Connecticut Ornithological Association; and the Connecticut Butterfly Association.
Part of the festivities included catching and tagging monarch butterflies (Danaus plexippus) that stop there to feast on flower nectar on their journey south. The public was encouraged to participate, snagging the beautiful creatures with nets and bringing them to representatives of the Connecticut Butterfly Association, who had a display table set up at the fair. Gary Lemmon, one of the founders of CBA, said, “We showed guests a chart of the life cycle and migration routes of the monarchs.”
“There could be up to ten people, mostly children, hunting down monarch butterflies at any one time throughout the day,” Lemmon said. “Many of the children already knew something about monarchs from school. For tags, we used a sheet of paper with 25 tags. Each tag is less than a quarter of an inch long. The underside of the tag is covered with glue. And we peel it off the sheet and attach it to the underside of the rear wing of the butterfly. The catchers would give the nets to one of the three of us at the table, we’d take the butterflies out if the nets, tag them, then hand them to the children, who’d let them go.”
Monarch butterflies get their common name from their regal appearance. Their wings are bright orange with black veins and white spots along the edges. Almost as flamboyant as the adult, the caterpillar or larva is striped vivid white, black, and yellow. The butterflies are large, with a 10 cm (4 inch) wingspan. Monarchs read their world with scent and color vision, and can see into the ultraviolet. They taste with their feet.
The caterpillars and adult monarchs are brightly colored and patterned to warn predators that they are foul-tasting and poisonous. The monarchs become poisonous by absorbing milkweed sap, which contains cardiac glycosides.
The butterflies will follow their migration routes to the southern United States and finally to mountain forests in the oyamel fir forests in the Michoacan hills in central Mexico, where they’ll spend the winter. Hundreds of millions of monarchs roost in the fir trees. Field workers monitor the populations, recording the script on the tags, which is a code of three numbers and three letters. The information goes to a database at Monarch Watch, an affiliate program with the Kansas Biological Survey at the University of Kansas.
In February and March, in Mexico, the monarchs mate. In March and April, that generation of monarchs flies north into the temperate zone to begin the first life cycle of the season, the females laying eggs on the way, up to 250 per day, on several species of milkweed, the only food source for monarch caterpillars. The most preferred species is common milkweed, Asclepias syriaca. Four (sometimes three) generations of butterflies live subsequently. The last generation migrates, while the other generations live for only about six weeks. The second generation will arise in May and June, the third in July and August, and the fourth and last in September and October.
So far, we’ve been discussing monarchs that live east of the Rocky Mountains. Another population of monarchs lives west of the Rocky Mountains. These migrate for the winter to southern California, and some of these fly to Mexico to join their brothers and sisters. Still another population lives in Florida but does not migrate.
Monarch eggs hatch in about four days. The caterpillar feeds on the milkweed, sometimes devouring a leaf in five minutes, and will be full-grown in about two weeks, molting five times and increasing its weight about 2,700 times. After the last moult, it transforms into a pupa or chrysalis, within which, over about ten days, it transforms into the adult form. After emerging, the adult lives for two to six weeks, feeding on flower nectar.
The monarchs found in North America constitute a single species, Danaus plexippus. Another species, Danaus erippus, lives in South America, and both are found on islands of the Caribbean. Danaus plexippus can also be found in Australia, New Zealand, some Pacific Islands including Hawaii, and Europe.
Monarchs are in trouble. Their numbers east of the Rockies have declined by more than 90 percent since 1995. In 1986, the government of Mexico established 62 square miles of forest as the Monarch Butterfly Biosphere Reserve. Conservation efforts include raising and releasing monarchs and planting milkweed and nectar-producing plants in strategic spots on the migration routes. Which brings us back to tagging monarch butterflies. According to Lemmon, “This year, we only tagged six or seven monarchs. In the past, it’s usually been 100-150 for the Migration Festivals. Something major is going on to account for the loss.”
CBA member Mary Ann Nazarphyk added, “For the last two years, we’ve had almost no monarchs, maybe six or seven, and the two years previous, a few more. Some of our tagged monarchs have been collected in Mexico. Kids are so aware of the monarchs. They’ll say, ‘I know all about them,’ and their information is correct. When we let the children handle them, it makes an impression they don’t forget. It’s a lot of fun for everybody. If it helps promote conservation, all the better.”
For further reading:
– Connecticut Butterfly Association
Kevin Fitzgerald is a freelance science writer living in Connecticut. He has published in newspapers, encyclopedias, and online.
The eastern USA monarch migration is not “in trouble” because there are still about 4 billion milkweed plants in the eastern USA that support a population of about 200 million migratory monarchs. It would probably take another century of urban sprawl to reduce those numbers in half and even then the migration would not be threatened with extinction because elsewhere in the world (e.g. New Zealand, Portugal and Australia) the seasonal migration phenomenon persists even though the numbers of milkweed plants and monarchs are around 1,000 fold smaller than in the eastern USA.