Donna Bush
A mature monarch chrysalis
The monarch butterfly has long been an object of wonder. Its dramatically contrasting orange, black, and white aggressively capture the eye, possessing the mystery of starting life as one creature and morphing into another. And then, there is the improbable specificity that dictates this insect’s little life—from what it eats, to where it flies, to where it dies.
The typical migration of monarchs is a multi-generational journey that, for the Central Mexican population (part of the Eastern population of monarchs, as opposed to the Western, which overwinters along the California coast), begins high in the oyamel fir forests of Mexico’s Sierra Madre mountains. Millions of monarchs spend their winters in these high forests between 7,875 and 11,800 feet. The wetness of the forest provides much needed moisture to aid their survival. Cooler temperatures allow them to slow their metabolism and conserve fat reserves as they gather together for warmth and protection.
When spring approaches, the hibernating monarchs awaken and begin their search for a mate. Then, they start their journey north and east, typically mid-March. Females will lay their eggs on milkweed plants along the Southern Gulf Coast of the United States, producing the first generation of the wintering Mexico monarchs.
After about four days, the caterpillar will hatch, ingesting its egg casing before devouring more milkweed leaves than you can imagine. At about two weeks old, the caterpillar will find a place to attach itself, hanging in a J formation, ready to form a chrysalis and begin the process of metamorphosis.
From the outside, it looks like nothing is happening. However, over the next ten to fourteen days, new tissue growth is being nourished by a specialized set of cells. The brain, the heart, and digestive tract form; flight muscles and compound eyes develop, legs grow long, and sturdy wings emerge. When the bright green chrysalis turns black, it means the monarch is about to emerge. Long legs hang onto the shell of the chrysalis as the new insect pumps its wings, causing them to expand. The wings must dry before the butterfly is able to fly.
After feeding on flowers, the monarchs will mate and move further north, where females will lay eggs on a new patch of milkweed. This first-generation monarch will only live two to six weeks, dying after laying its eggs. Males typically die shortly after mating.
The cycle continues, traveling and birthing and being born and traveling yet some more, until the final generation reaches the Northern U.S. and Southern Canada; this can sometimes take five generations. The last spawns a super butterfly, which will live up to eight times longer than its mother, grandmother, great-grandmother, or great-great-grandmother. If all goes according to plan, the super butterfly will fly all the way from wherever it emerged to the Mexican oyamel forests to overwinter. When he/she makes this long trek, they enter a physiological state known as diapause. Their reproductive organs do not develop until after the next winter, making them lighter and more efficient fliers for their long journey.
For years, scientists have warned about the alarming decline of the monarch butterfly—whose population in North America has decreased more than eighty percent since the 1990s. This loss has many causes, but the most prominent are habitat loss caused by increased logging and development, and the loss of milkweed breeding grounds.
As recently as December 10, 2024, the United States Fish and Wildlife Service announced a proposal to list monarchs as threatened under the Endangered Species Act, with species-specific protections such as prohibiting anyone from killing or transporting the monarch and protecting properties with milkweed. (The public comment period for the proposal ends on March 12.)
The battle cry has long been “Save the Monarchs! Plant Milkweed!” And many people, captivated by these fascinating creatures, have answered the call.
Donna Bush
A released female monarch
The problem, according to ongoing research, is that people are planting the wrong species of milkweed.
The milkweed most available at local nurseries, known as tropical milkweed (Asclepias curassavica), is native to the Caribbean—attractive because it can easily survive our region’s mild winters, flowering and leafing year-round.
However, unbeknownst to most monarch-lovers, tropical milkweed is more likely than natives to harbor a parasite called OE (ophryocystis elektroscirrha), which can be deadly for monarchs.
If, when a female monarch lays her eggs on a milkweed plant, she or the plant is infected, the disease will be passed along to her offspring as they hungrily munch away on the leaves. Infected butterflies may be too weak to emerge from their chrysalides, or may make it out deformed or with crumpled wings, unable to fly.
In some cases, the monarchs might look normal but not be healthy enough to live long or survive migration. If, by chance, the new butterfly survives and can fly, it will be infected and will pass along the parasite spores to mates and other milkweed plants it lands on. This is a vicious cycle with devastating impacts to the population. The OE spores can only be detected with a microscope, making it more difficult for conservationists to target and fight.
“People are planting non-native milkweed thinking that they are helping. This results in the monarch laying eggs in their non-breeding season when they should be migrating to Mexico.” —Dr. Andy Davis, Research Scientist with the Odum School of Ecology, University of Georgia
According to Dr. Andy Davis, Research Scientist with the Odum School of Ecology, University of Georgia, who has studied monarchs for twenty-five years, OE can be found on native milkweed as well as the tropical species, but remains on non-natives longer, allowing the spores to accumulate. “But in areas of extreme OE prevalence,” he said, “there is OE on every milkweed on the landscape.”
A major hotspot, and an alarming interruption in the monarch migratory cycle, is the Gulf Coast. Thanks to the citizen science program, Project Monarch Health, run by the University of Georgia, we know that destinations along the Gulf Coast are experiencing extremely high rates of OE-infected milkweed. In parts of New Orleans, OE prevalence rates have been found in 100% of samples tested.
In addition, because tropical milkweed doesn’t always die out at the same time that native milkweed would, the monarch’s migratory and reproductive rhythms can be affected.
“There’s a real fear in the scientific community that these non-native milkweeds, especially in the southeast, are basically telling the monarchs not to migrate,” said Davis. “People are planting non-native milkweed thinking that they are helping. This results in the monarch laying eggs in their non-breeding season when they should be migrating to Mexico.”
Dr. Davis recommends that residents of the Gulf Coast avoid planting any milkweed, especially the tropical milkweed, to help lower the high OE infection rate. He also discourages people from raising monarchs in captivity. “Basically, you are rearing infected monarchs, releasing them into the wild to contaminate more milkweed,” he said.
Dr. Davis recommends, instead of milkweed, that people grow nectaring plants to provide fuel for the monarch’s long, arduous flights, encouraging them to continue to migrate, while preventing yards from becoming infection hotspots.
Right now, “Monarchs just need humans to let them do this on their own,” said Dr. Davis.
