The Monarch butterfly (Danaus plexippus) is a vital pollinator across much of North America. But the species is facing some of the same environmental pressures afflicting other insect pollinators, and the number of monarchs overwintering at sites in Mexico is declining precipitously.

Severe weather, logging, pesticide use and other factors all contribute to the decline in monarch numbers, said Gae Bergmann, a Master Gardener in Dodge County. During a May 26, 2016 talk on monarchs that aired on Wisconsin Public Television’s University Place, she discussed the biology of these butterflies and how people can help bolster their numbers.

The species requires a very specific form of habitat in the form of various milkweed plants, an essential component of the butterflies’ development. Bergmann explained how the conversion of 147 million acres of cropland and grassland to commercial or residential spaces across the continental United States has affected the species, and noted its broader role in the environment.

“Monarch butterflies are important pollinators, they are part of the health of our ecosystems,” she said. “If we don’t have pollinators, we are in deep trouble.”

Bergmann described steps people in Wisconsin can take to bolster monarch numbers, with seeding milkweed chief among them. (A U.S. Geological Survey study published in February 2017 found that around 1.8 billion more milkweed plant stems are needed across the Eastern monarch butterfly’s North Central range in the United States to restore the population to sustainable numbers and forestall its extinction.)

Bergman also advocated the planting of other nectar plants, and, given the time and resources, direct collection of monarch eggs and care for developing caterpillars.

While monarchs are a migratory species, the specific butterflies departing Mexico are not the same as those that arrive in Wisconsin in late spring. Monarchs perform their northern migration in multiple stages. Beginning in February or March, one generation flies a portion of the total migratory distance, mates and lays the eggs of butterflies that will complete the next leg of the journey, and subsequently dies after two to six weeks. Bergmann noted the final generation in this cycle, born in September or October, will live for six to eight months to complete the return migration to overwintering sites in warmer southern climates.

Adult monarchs lay small, pale green football-shaped eggs on the undersides of milkweed leaves, which present them a ready supply of food for the larvae after hatching. Smaller than the head of a pin, these eggs are highly vulnerable to predators and weather, said Bergmann, and have a survival rate of just 5 to 10 percent.

To improve the survival odds of monarchs, Bergmann creates specialized habitats for their eggs and caterpillars. She collects milkweed leaves bearing the tiny eggs, wrapping the cut ends in wet paper towel covered with aluminum foil to keep them fresh. These eggs, placed in small containers with holes drilled from the inside out to eliminate sharp edges, will usually hatch in one to four days after collection.

As it consumes the milkweed in its cage, a newly hatched caterpillar will go through several stages of growth, which are called instars. As it grows, the caterpillar sheds and consumes its skin, eventually reaching a length of around two inches. At this size, Bergmann places the insect in a larger container in anticipation of metamorphosis.

Monarchs require a little maintenance at every stage of development.

“Cages should be kept dry, they should be kept clean, and they should be full of leaves for your caterpillars,” said Bergmann.

A monarch preparing to enter chrysalis will hang from the top of a habitat container in a “J” shape for one to two days, eventually straightening out and forming the thick green shell it occupies for 10 to 14 days as it undergoes the transformation from caterpillar to butterfly. The chrysalis darkens, then becomes opaque as the monarch nears emergence. The butterfly’s thorax and wings will be half their fully grown size when the insect leaves its cocoon, and it will need to remain undisturbed for up to 24 hours for its wings to dry.

Bergmann said she applies tags from the Monarch Watch program (an affiliate of the Kansas Biological Survey) on the butterflies she raises once they are hatched and healthy. These tags aid in research and conservation efforts, and can update Monarch Waystation owners on the progress of their butterflies. She gently applies a tag to the wing of a butterfly and releases it on its southern journey.

Key facts

• Monarch butterflies develop over four stages: eggs, larvae (or caterpillar), pupae (or chrysalis), and adults. This life cycle is usually repeated four times in a single year, as successive monarch generations complete different portions of the species’ migratory journey. The monarch is the only butterfly species that migrates in this way.
• Newly hatched monarch caterpillars cut milkweed leaves into small circles before consuming them. Milkweed contains sticky latex, which causes the caterpillars’ tiny mandibles to become stuck together. This behavior, called trenching, cuts off the flow of the fluid, drying out the leaf section and rendering it safe to eat.
• The presence of two spots on the wings of an adult butterfly differentiates male monarchs from females. Wing strength and color intensity increases in each successive generation, reaching full potential in the generation performing the return migration to warmer climates.
• In the 1990s, the land area occupied by monarch butterflies dropped from a high of around 18 hectares to a mere 1.3 hectares in 2015. (A hectare is 10,000 square meters, and equivalent to just under two-and-a-half acres in size.)
• Monarch butterflies tend not to fly in temperatures of less than 56 degrees Fahrenheit. People who tend monarchs can lend a hand on cold fall days, though. Just prior to their migratory departure southwards, adult butterflies may need to feed indoors on nectar from flowers. If disinclined to gain nourishment in this way, the butterflies can be placed in a shallow container, like a jar lid, filled with a 20 percent sugar solution or hummingbird nectar. After eating, the butterflies’ feet should be gently rinsed in clear water.
• A Monarch Waystation is a habitat intended to foster monarch butterfly populations on their migration. A program of Monarch Watch, the requirements for a waystations includes exposure to six hours of sun per day and a collection of milkweed and nectar plants, planted close together to give butterflies optimal protections from predators and the elements.
• Monarch butterflies are the subject of another episode of University Place, recorded in February 2015 at the Wisconsin Garden Expo. This presentation offers additional information on the migratory patterns of the insects and more tips for caring for them at home.

Key quotes

• On steps that help and attract monarch butterflies: “The first thing we do is plant milkweed. Try not to use pesticides. It’s just whatever you’re going to use can also do a number on your butterflies. Plant some milkweed. Add nectar plants. Anything that has nectar on it the butterflies will thank you for because it’s their food. Plant some milkweed. Convert some of your lawn to butterfly habitat. Twenty-eight million acres in this country are nothing but lawns. They don’t have to be that. Plant some milkweed. Convert some of your lawn to habitat. Plant some milkweed.”
• On housing developing butterflies: “The containers that you put your monarch caterpillars in and eggs don’t make any difference when they’re small. You do need to aerate them, ventilate the containers. So I poke a hole from the inside out because when they go up to the top, you don’t want them to impale their little selves on the plastic that’s on the bottom. You can put them in glass jars, you can put them in anything. I put them in any kind of plastic container that’s available. The smaller they are, the smaller the container can be.”
• On the durability of chrysalis: “The final chrysalis… it’s a very sturdy and long-lived cage. We go to the U.P. and go to my brother’s nine miles on a logging road. I have never had a chrysalis fall off the cage. They’re very, very sturdy structures.”
• On one cultural aspect of monarch butterflies in Mexico: “One of the most important things about the economy of certain countries is the trips that people take to see the butterflies which are roosting in the trees. And on November 1, that is called the Day of the Dead … this is the day that many Mexicans feel that the coming, returning butterflies, each one holds the soul of one of its dead people, one of its ancestors.”
• On the importance of monarchs: “Most butterflies, most insects, actually, matter, but some of them matter more than others. As far as I’m concerned, monarchs are the most important, of course. They have been around for more than 50 million years, which just boggles your mind. They’re part of our basic biodiversity in this land of ours. They have been part of literature …since the Bible was prepared.”