New monarch numbers encouraging


A monarch butterfly eats nectar from a flower. The number of monarchs has declined 80 percent in the past 20 years, partly due to the loss of milkweed and nectar-producing flowers. The butterfly’s larvae eat the milkweed and the adults eat the nectar.
PHOTO COURTESY OF JACQUELINE POHL/IOWA STATE UNIVERSITY A monarch butterfly eats nectar from a flower. The number of monarchs has declined 80 percent in the past 20 years, partly due to the loss of milkweed and nectar-producing flowers. The butterfly’s larvae eat the milkweed and the adults eat the nectar.

AMES — The World Wildlife Fund released its 2018-2019 overwintering monarch population report last month, and it contains great news for the fluttering fellows. Adult monarch butterflies covered approximately 15 acres of forest canopy in Mexico, a doubling of last year’s population, and a level not seen since 10 years ago.

The report provides hope, say leaders of the Iowa Monarch Conservation Consortium.

“Although the number of monarch butterflies overwintering in Mexico has rebounded considerably, turning this encouraging one-year population response into a consistent long-term trend depends on advancing conservation efforts that are critical to help monarchs survive and reproduce in Iowa and the Upper Midwest,” said Steve Bradbury, professor of natural resource ecology and management at Iowa State University.

Milkweed loss

Monarch butterflies face many challenges including the loss of milkweed and nectar plant habitat in its spring and summer breeding ranges. Female monarchs lay eggs exclusively on milkweed plants. National and state efforts focus on establishment of new milkweed habitat to reach conservation goals.

“This year’s high watermark is very encouraging, and Iowa has a critical role to play in providing summer breeding habitat for the monarch for years to come,” said Bruce Trautman, acting director of the Iowa Department of Natural Resources. “We have a really strong group with broad expertise working together to support the monarch recovery in Iowa and beyond.”

Habitat plantings include milkweed and a diverse array of blooming species to provide nectar for adult monarchs throughout their life cycle and seasonal migrations. The current Iowa Monarch Conservation Strategy seeks to establish approximately 480,000 to 830,000 acres of monarch habitat by 2038. Iowa’s strategy, combined with those of neighboring states, is designed to consistently maintain a yearly population of 225 million adult monarchs, or about 15 acres of occupied forest canopy.

“The monarch butterfly population numbers are encouraging and serve as a reminder of the importance and impact of our ongoing conservation efforts,” said Mike Naig, Iowa Secretary of Agriculture. “Iowa’s long-term strategy includes expanding habitat for monarchs on our agricultural land, urban areas, roadsides and other public land.”

Iowa consortium

The Iowa consortium is a group of 50 organizations, including agricultural and conservation associations, agribusiness and utility companies, universities and county, state and federal agencies. Roughly 40 percent of all monarch butterflies that overwinter in Mexico are estimated to come from Iowa and neighboring Midwestern states. Expanding monarch habitat in Iowa will play a major role in the recovery of the species.

“Progress always starts with good science, and our researchers continue to make strides to understand what it takes to improve and increase monarch habitat through a deeper understanding of biology and the environment,” said Daniel Robison, Endowed Dean of the College of Agriculture and Life Sciences at Iowa State University. “Our extension and outreach efforts, in coordination with regional, national and private partners, are doing much to provide the science-based information and education that ensures approaches to monarch conservation are as effective as they can possibly be.”

The Iowa strategy — developed by consortium members — guides the implementation and documentation of voluntary, statewide conservation efforts based on the best available science. Their approach fosters habitat improvements in rural landscapes that do not conflict with agricultural production, are sufficient in scale to support improved monarch breeding success and strive to complement other conservation programs.

Why have monarchs rebounded?

Bradbury said monarch butterflies have had a rough go of it lately. Their population has declined about 80 percent in the past 20 years due in part to a loss of habitat. Why, then, did their numbers rebound so well this past winter? Bradbury said the conservation efforts are too young to have had such a dramatic effect. Instead, he said it was because last year’s weather was ideal for these migrating insects.

Monarch butterflies follow a migrating pattern unique in the animal world. The butterflies spend the winter in Mexico where it’s warm year-round. They start heading north in the spring to find milkweed, which is the only plant the females will lay eggs on. Why? It’s the only food their larvae eat. Bradbury said this might have to do with both the nutrients the plant provides and, oddly, the toxins.

Milkweed contains compounds that are toxic to birds, which like to feast on larvae. Bradbury suspects that, through many centuries of natural selection, eating milkweed was a kind of defense mechanism for the young caterpillars, and the birds learned to avoid them.

The spring of 2018 brought cool weather to Texas. That prompted the monarchs to stay farther south than normal. Bradbury said that, if the spring is too warm, monarchs will fly north too soon before the milkweed has had a chance to grow, and they will starve. That didn’t happen last year, which explains why so many monarchs were around to make the return trip to Mexico by the winter of 2018-19.

Life cycle

According to, monarchs live for two to six weeks in their adult, flying stage. After a female lays her eggs, they need only four days of incubation before hatching as larvae. The larva munches on milkweed and lives life as a caterpillar for two weeks before building its chrysalis. It remains in the chrysalis for 10 days before metamorphosing into a beautiful butterfly. Every six to eight weeks, another generation is born, each one traveling hundreds of miles north during its short lifespan.

By the time October rolls around and it’s too cold to go any farther north, the monarchs have reached Minnesota, Wisconsin and sometimes even Ontario, Canada. They are four or five generations removed from their ancestors who lived in Mexico. And yet, the monarchs make the 2,500-mile “return” trip to Mexico, a place they’ve never been.

How is this possible? How can the butterflies know to fly to the same forests once inhabited by their four times great-grandparents? Bradbury calls it a “mystery of evolution.” Birds and fish migrate, too, but they’re returning to a place they called home as a young offspring. The monarchs migrate to an unfamiliar land.

Bradbury said the monarch’s migratory pattern might be related to the glacier that once covered most of North America. As the ice receded, milkweed was able to survive at higher and higher latitudes, so the butterflies moved with it. The butterflies that stayed north too long died. Over time, the butterflies developed a gene that told them to fly south when the temperature dropped or the days got short. Bradbury said entomologists aren’t sure of the exact mechanism, but think it must be something along those lines.


Bradbury said the reason for the 80 percent drop in monarch population in the past 20 years is multifaceted. Scientists agree that the loss of breeding habitat in the upper Midwest is a major factor.

Why is there less milkweed than before? Quite simply, farmers have become more efficient in eliminating weeds from their fields. Decades ago, at least some milkweeds found their way into corn and bean fields, but many fewer milkweeds do so today.

“Some of the decline in milkweed can be explained through the ever increasing urbanization of the landscape,” Bradbury added.

That has meant the monarchs have had to travel farther to find their sacred plant.

Larvae need milkweed to survive, but adults eat something else: nectar. Bradbury said there are fewer nectar-producing plants than before as well, which means the adults don’t have enough energy to make the arduous trip to Mexico.

Another stressor on the butterflies is extreme weather in Texas and Mexico. Bradbury noted that droughts in Texas played some role in the monarchs’ decline. Ice storms in the mountains northwest of Mexico City can hit the monarchs hard, too.

Luckily for the humans trying to help the butterflies, monarchs don’t need huge acreages of milkweed and nectar-producing flowers. In fact, they prefer lots of little patches of habitat throughout their journey.

Could monarchs go extinct?

Bradbury said the likelihood of monarchs going extinct is low because there are non-migrating monarchs in Mexico and Central America not nearly as affected by the loss of milkweed as the migrating variety.

“Our concern is that, if the number of monarchs gets too low, the migration north could go extinct,” Bradbury said. “Monarch numbers got really low about six years ago. If there had been a big ice storm in Mexico over the winter of 2013-14, we could have lost the migration that year.”

Conservation efforts

Bradbury is extremely pleased with the conservation efforts in Iowa, which are viewed as a model throughout the Midwest. He’s thrilled to see so many groups, from Iowa State University to the Iowa Department of Natural Resources to agricultural associations, get behind the push for more habitat for monarchs.

What you can do

The Iowa Monarch Conservation Consortium has published five ways people can help monarch butterflies. They are:

1) Take advantage of Farm Bill programs to establish breeding habitat such as milkweed and nectar-producing plants. These benefit not just monarchs but other pollinators.

2) Establish monarch habitat on your land as part of a demonstration project. The Iowa Natural Heritage Foundation and partners, through the Monarch Butterfly Flyway Project, are restoring/installing monarch habitat along three north-south migration corridors in Iowa. This project will partner to cost-share new pollinator seeding on public land or permanently protected private lands.

3) Follow federal pesticide labels and state regulations when applying pesticides labeled as toxic to bees to avoid unnecessary exposure to pollinators and monarchs. Adjust spray equipment to reduce drift by using low pressures, large droplets, and low boom heights. Avoid applications when wind speed is above 10 miles per hour or wind direction is toward monarch habitat.

4) Consider monarch-friendly weed management recommendations for roadsides and other rights-of-way. Roadsides offer options for miles of monarch habitat (milkweed and nectar plants). Ask the Iowa DOT or your county roads department to avoid spraying or mowing your roadside, and for permission to plant or maintain native plants in your roadside.

5) Establish a Monarch Waystation, a garden with both nectar plants and milkweeds, where monarchs can find nectar and reproduce. Monarchs lay eggs on milkweeds, the only food monarch caterpillars eat. Adults need flower nectar from spring to fall.