About Butterflies and Moths – Part 6
By Mary Free, Extension Master Gardener
Since the mid-1990s, the population of eastern monarch butterflies has declined by about 85 percent. This year’s population count, released in May 2022, showed a slight uptick in the number of occupied acres of winter habitat in Mexico. Unfortunately, it amounted to only abut 7 acres – well under the circa 14.8 acre extinction threshold that scientists estimate monarchs must maintain for their long-term survival.
Reasons for the decline include loss of summer breeding grounds due to agriculture and suburban sprawl, habitat fragmentation, chemical use (herbicides that kill milkweed and pesticides that kill monarchs), climate change, and more recently, an increase in illegal logging in the Mexican butterfly reserves. Since the 1990s, North American monarchs (east and west) have lost about 167 million acres of breeding ground – more than four times the size of the State of Virginia. The U.S. Fish and Wildlife Service has yet to act on a petition to recognize monarchs as a threatened species under the Endangered Species Act.
Monarchs travel through the Mid-Atlantic Region every year on their way north to breed and on their way south to overwinter in Mexico. They stop here to rest and fuel up on nectar for their journeys as well as to breed. Monarchs could benefit from protection of strategic habitat along their flyways. A few states, including Virginia, have enacted legislation to identify wildlife corridors and address barriers to wildlife movement. Establishing and protecting such corridors nationwide is part of an integrated strategy to address both climate change and biodiversity loss. In 2021, the House of Representatives passed the bipartisan Wildlife Corridors Conservation Act introduced by Representatives Don Beyer (D-VA) and Vern Buchanan (R-FL). The Senate is working on its own legislation.
What You Can Do to Help
Until wildlife corridors are established and protected nationwide, it is up to individual citizens to take action. You can help monarchs by integrating some of the plants that they favor into your existing gardens or by creating a monarch “waystation” that provides host and nectar plants that monarchs need to produce successive generations and sustain their migration.
Left to right: Glencarlyn Library Community Garden Monarch Waystation, Bluemont Park Monarch Waystation (sign and flowers), Simpson Park Demonstration Garden butterfly soak.
- Size: Monarch waystations of at least 100 square feet are most effective. If you cannot devote that amount of contiguous space, then try to establish several smaller sites on your property. If you are limited to patio or balcony gardens, then try to incorporate some monarch host and nectar plants into your existing space. If you live in a community with common grounds, you may want to talk to your community association about creating a monarch waystation or planting a patch of milkweed plants. One advantage to having discrete areas devoted to monarch plants is that you don’t have to worry about the garden’s untidy appearance. Dead foliage and flowers, which may harbor eggs or developing caterpillars, can remain without distracting from other flowers as they might in more formal garden settings.
- Host Plants: For best impact, include at least 10 milkweed plants of two or more species. Monarch egg counts are higher when more than one milkweed species is present. In experiments with nine milkweed species, monarch egg counts were highest on Asclepias incarnata (swamp milkweed). In choice experiments with four milkweed species, monarch “females laid 1.7 times more eggs on A. incarnata than on A. syriaca …, 14.9 times more eggs than on A. tuberosa … Females laid nine times more eggs on A. syriaca than on A. tuberosa” (Pocius, 2018).
- When space is limited, consider natives Asclepias incarnata and Asclepias tuberosa (butterfly-weed), both of which are better behaved in smaller gardens. They require different habitats–swamp milkweed tolerates wetter soil, clay, and some shade while butterfly-weed tolerates dry/poor soil and drought but prefers full sun. The length and timing of flowering also differs somewhat. Having both plants in a landscape would be advantageous to monarchs, because if a season is wetter or drier or hotter than normal, then at least one of these milkweed species should still perform well and be a viable and healthy host.
- For larger areas include native Asclepias syriaca (common milkweed). It has rhizomes, which can spread quickly to form colonies. However, 450 insects have been known to feed on its different parts and it produces rich nectar day and night to attract both diurnal and nocturnal pollinators.
- Refrain from planting tropical milkweed. Unlike native milkweeds, tropical milkweeds bloom late into the season. It is a topic of debate whether this confuses monarchs into breeding when they should be migrating or overwintering. Additionally in mild climates where this tropical milkweed does not die back, a monarch butterfly parasite, Ophryocystis elektroscirrha (aka OE) can remain on the leaves to be ingested by succeeding generations of caterpillars, in turn infecting and weakening adults.
Left to right: Monarch butterfly and caterpillar on Asclepias incarnata, monarch butterfly and caterpillar on Asclepias tuberosa, and monarch butterfly and early instar on Asclepias syriaca.
- Nectar Plants: Female monarchs deposit their eggs on milkweed during the breeding season (late spring through summer in Northern Virginia) and their caterpillars devour the leaves as they grow. During this time, adult monarchs may feed on milkweed flowers, but they usually have many other nectar choices (see Nectar and Host Plants for Selected Mid-Atlantic Butterflies and Moths and Monarch Nectar Plants for the Mid-Atlantic for their preferred flowers). Monarchs migrate from the northeast through Virginia in September and October on their way to Mexico. They require the sustenance of nectar-rich, late-season bloomers like asters (e.g., Symphyotrichum novae-angliae, S. laeve), goldenrod (Solidago spp.), and native thistle (Cirsium spp.) so they have the energy they need to make the journey.
- Siting: The same guidelines for attracting other lepidopterans apply to monarchs. Allow for a succession of blooms from early spring to greet the first monarch arrivals through fall to nourish the last of the migrators. To capture a monarch’s attention, group three or more plants of the same species together in a mass rather than single plants of different species. Plant densely (follow the low end of spacing recommendations) to allow for efficient feeding and to shelter developing caterpillars from weather and predators. Although butterflies prefer sunny locations, they use plants in partial shade if sunny basking areas are nearby.
- Maintenance: Like all gardens, the waystation will require routine upkeep with watering, mulching, pruning, removal of invasive species, and clean-up of dead materials at the appropriate times. However, maintenance should NOT include the use of chemicals!
If you decide to create a monarch habitat, you can have it certified as an official Monarch Waystation by Monarch Watch.
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- Betz R.F, et al. 1992 Insect Pollinators of 12 Milkweed (Asclepias) Species. Northeastern Illinois University, Chicago, Illinois.
- Eastern Monarch Butterfly Population Up Slightly, Still Below Extinction Threshold. May 24, 2022. Center for Biological Diversity.
- Eldredge EP. 2015. Milkweed Pollination Biology (Asclepias spp.), Natural Resources Conservation Service, Plant Materials Technical Note NV-58, United States Department of Agriculture.
- Monarch Waystation. Program. Monarch Watch. (accessed June 5, 2022)
- Pocius VM, et al. 2018. Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species. Ecosphere 9(1):e02064.10.1002/ecs2.2064. https://doi.org/10.1002/ecs2.2064
- Tried and True Native Plant Selections for the Mid-Atlantic. Master Gardeners of Northern Virginia