By Bev Thierwechter
Piedmont Master Gardener
In July, the International Union for Conservation of Nature classified the migratory monarch butterfly as endangered and declared it “at risk of extinction” in the United States and Canada. The U.S. monarch population has declined between 22 and 72 percent over the past decade, varying due to seasonal events. Longer-term trends are even more telling. The number of monarchs in the western U.S. has fallen approximately 99.9 percent since the 1980s, and the much larger eastern population shrank by 84 percent from 1994 to 2014.
If these trends continue, this colorful butterfly will disappear from our yards and gardens. We can improve the outlook for monarchs by creating home habitats and adopting practices that support these beautiful creatures.
The Marvel of the Monarch
Why do monarchs capture our hearts? Known for their impressive annual, multi-generational migration of up to 3,000 miles to wintering grounds in Central Mexico and southern California, they add beauty to our landscapes along the way. They also fascinate us with their complex life cycle and behavior, which is not fully understood. Along with bees, bats, birds and other wildlife, they pollinate many food crops we rely on and help flowering plants reproduce.
Migratory monarchs (Danaus plexippus plexippus) are also easy to recognize. They have two pairs of bright orange-red wings with black veins, a border of white spots along black wing edges and a black body with white markings. The slightly bigger males are identifiable by their thicker veins and two dark spots in the center of the hind wings.
The monarchs, like most insects, undergo complete metamorphosis with four stages of development: eggs, larvae, pupa and adult. They lay eggs on milkweeds, the only host plant for their yellow, white and black striped caterpillars. They hatch in three to five days, molt several times over a couple of weeks and then build an oblong green capsule (chrysalis) around themselves. After about two weeks, the caterpillars transform into full-sized adult butterflies. Adult monarchs live between two to six weeks, except for the last generation of the year, which lives about eight months and completes the long-distance fall migration.
As the National Wildlife Federation notes, “the monarch migration is one of the greatest phenomena of the natural world,” the most highly evolved migration pattern of any butterfly or moth. There are separate migration routes for the eastern and western monarch populations, and fall migration is triggered by shorter days and lower temperatures.
In the east, the butterflies begin their migration south in eastern Canada and the northeastern U.S. Monarchs travel 25 to 30 miles per day and arrive at specific sites in the mountains of Central Mexico about two months later. They roost there in large clusters on the oyamel fir trees. After hibernating until February or March, they mate and follow the same flyways north, searching for milkweed on which to lay their eggs. The generation that completes the journey southward and the winter hibernation will die during the migration north, and its offspring will continue on.
It typically takes two generations to reach the migration’s northern limit and then another two to return to Mexico. Then the amazing cycle begins again.
The migration process for the western population of monarchs is similar, but they travel a shorter distance from northwestern Canada and the Pacific Northwest to the central or southern California coast for winter.
How do monarchs find their way to the same winter destination each year? Scientists speculate that the earth’s magnetic field, the position of the sun or other environmental cues may play a role.
The Threat to Monarchs
Many factors seem to contribute to declining monarch numbers. Illegal logging in Central Mexico’s mountains has reduced the habitat butterflies need to survive. All along their migration route, urban development, agricultural and domestic use of herbicides and pesticides have destroyed much milkweed. Severe heat, drought, cold or heavy rains can reduce their numbers.
Researchers also suspect that planting the late-blooming, nonnative tropical milkweed (Asclepias curassavica) in the southern states may cause monarchs to forgo migration and remain where they cannot tolerate the colder winter temperatures. In addition, this plant can harbor high concentrations of the spores of a parasite known as Ophryocystis elektroscirrha or OE, which threaten the overall health and survival of monarchs at each stage of their development.
Conservation Starts at Home
Growing fascination with monarchs has inspired governments, local communities and non-profits to promote all kinds of efforts to protect them. What can we do as gardeners? Monarchs need a welcoming habitat that provides shelter, water and food, all of which can be provided in our own backyards. Here’s how:
Plant milkweed, the only type of plant on which monarchs lay their eggs and the only food source for the caterpillars. The August 2022 issue of Piedmont Master Gardeners’ online newsletter, The Garden Shed, recommends five milkweeds suitable for Albemarle County and refers to three useful native plant data bases to consult on milkweed varieties for specific areas of the country.
Plant nectar plants to provide food for adult monarchs. The Xerces Society offers a series of helpful Monarch Nectar Plant Guides for the Mid-Atlantic and other regions of the U.S. (xerces.org).
Avoid use of herbicides and pesticides. Herbicides can kill both milkweed and nectar plants, and pesticides can threaten monarchs and other pollinating insects.
Participate in citizen science projects that monitor monarch migration or collect other monarch data. Monarchwatch.org and Monarchjointventure.org are two of many websites that offer monitoring opportunities.
Educate others about ways to protect monarchs and help raise awareness of monarch conservation efforts. The options are many. For example, Monarch Watch offers free milkweed plugs to schools and nonprofits, and the National Wildlife Federation has programs for schools, children and families (nwf.org).
Come See a Pollinator Garden Sept. 30
To see a good example of a garden that supports monarch butterflies and other pollinators, come to a free open house between 10 a.m. and noon on Friday, Sept. 30, at The Center at Belvedere. The newly designed and planted pollinator demo garden is at the back of The Center, off Rio Road at 540 Belvedere Boulevard. Drop by then and come back later to see the garden grow. For more details, view the garden design and plant list online at piedmontmastergardeners.org/gardening-questions/native-plants/.
Viewing Monarchs in Central Virginia
For those intrigued by these fascinating insects, note that the peak season for spotting monarchs migrating through Central Virginia is late August into September. And, in September, you can discover many monarch caterpillars feasting on an abundant buffet of milkweed at Big Meadows on the Skyline Drive in the Shenandoah National Park.