POLLINATORS IN CRISIS:DESIGNING FOR WESTERN MONARCH BUTTERFLY
Photo: Candace Fallon - Xerxes Society
The monarch butterfly is one of the most recognizable insects in America with their vibrant orange wings streaked with black and dotted with white. They are well known for making the incredible multi-generational migration journey from Central Mexico to the very northern reaches of the United States. A lesser known fact about these insects is that there are two main sects of monarch butterflies; the eastern, who overwinter in Mexico, and the western, who overwinter in forested groves along the California coast and whose range only extends as far east as the Rocky Mountains.
The Western Monarch butterfly today is undergoing an extreme population decline. An alarming count undertaken by the Xerxes society in 2018 indicated around 30,000 butterflies, and when the population was counted again in November of that same year there were fewer than 2,000. This collapse is almost a 99% decrease from 1980, when the population numbered at 4.5 million. (McCormick, 2021) The population of the western monarch butterflies has been in steady decline for the past few decades, but their steep drop has worried scientists about their potential extinction. Research into the problem, and possible solution, agrees that there are multiple factors impacting the butterflies- primarily habitat loss in overwintering places and use of pesticides (Xerces Society, 2021) (Pelton, et. al, 2019).
Figure 1
The warming climate has influenced the early - or late- blooming of critical plants, particularly the milkweed plant that butterflies rely on. Caterpillars eat milkweed exclusively in the first two weeks of life. Each caterpillar needs about 30 leaves before creating the chrysalis to transform into a butterfly (McCormick, 2021). The poisonous compounds of the plant help develop the bright orange color of the wings, and give added visual and chemical protection from predators as they take on the poisonous properties of their primary plant (US Forest Service, 2022). Due to the toxic nature of the plant and the classification of a weed in most states, milkweed is generally removed or discouraged from planting in neighborhoods, roadsides, and farmland. As a result, plant nurseries rarely carry this native plant. Pesticide use is widespread in the heart of the monarch butterfly’s summer nesting ground in the Mid Western corn belt as well as on California’s farmland. Much of the milkweed plants are in or near agricultural fields, whose use of herbicides on GMO plants have a negative impact on juvenile monarch butterflies and caterpillars (Center for Biological Diversity, 2022). The impact of the use of pesticides on California farms during the monarch’s spring migration and first breeding season can be seen in the above diagram, “Pesticides Impact on Breeding Zones”. Farms overlap with almost the majority of the monarch’s spring breeding grounds. A study conducted by Hulisandra in 2020 marked a strong correlation when a rise in Monterey’s winter butterfly population occurred after a decrease in pesticide use by the local farms (Hulisandra 2020).
The continuous construction of properties in California due to its popularity as a residential state is a key contributing factor in habitat loss. Urban sprawl is growing and developing land is encroaching upon various environmental habitats with healthy ecosystems. This clash of habitats can be seen by the increase in the amount of human - mountain lion encounters in the Santa Cruz Mountains. The continued development without a focus on replacing key vegetation for pollinators has had a negative impact on the monarchs. Landscape architects can make an impact in the critically small overwintering sites along the coast by advertising “pollinator gardens” in their offerings, or being aware of the most important milkweed, pollen plants, and trees that butterflies converge on and the critical zones where monarchs need these resources. Monarchs are most attracted to pine trees, the Monterey Cyprus, and Eucalyptus trees along the California coast where they have access to water and plenty of pollen flowers. Planting milkweed within 5 miles of the California coast is not advised, as it can disrupt their winter diapause cycle (Xerxes Society, 2021). Most nurseries do not carry milkweed because of its classification as a weed and general disuse from most projects. At a grass-roots level the market for more native plants can start to grow when more individuals and companies start demanding this product.
Photo: a pollinator garden from A Cultivated Nest
Policy is another way to help the monarch butterflies bounce back on a large scale. In 2021 the state of California undertook a massive effort, in collaboration with conservationists and biologists, to plant large swaths of native milkweed plants within the state, concentrating on the central valley where monarchs make their first stop after overwintering and reproduce. In the same year, Biden signed the $1 trillion Infrastructure investments and Jobs Act, which contains funding and specific requirements for the planting and care of local pollinator habitats on the side of roads and major highways (Jepsen, 2021). These landscape policies may be just in time to save our crucial pollinators. The timing of this policy passing has fortuitously coincided with the rebound in the monarch population. In 2021, the Monarch butterflies had a shocking population recovery, jumping from under 2,000 to 250,000 by California’s Xerces Society for Invertebrate Conservation (Greenberg, 2022). The additional aid that the monarchs will receive gives them an even greater chance to rebuild their population.
Landscapers and designers can take advantage of this dramatic comeback to help encourage and promote native plantings for pollinators. By understanding how one property is part of a larger ecosystem, developing landscapes can change to be more of a steward of our larger urban environment for resilience rather than an individual microcosm.
For more resources about what vegetation to plant in your garden, visit the Xerxes Society for more information about your particular area.
Works Cited
Center for Biological Diversity. “Saving the Monarch Butterfly.” Center for Biological Diversity, 2022. https://www.biologicaldiversity.org/species/invertebrates/monarch_butterfly/
Greenberg, Alissa. “Western monarch populations grew over 100-fold in 2021. Why?” PBS: Nova, 25 January 2022. https://www.pbs.org/wgbh/nova/article/western-monarch-population-growth-2021/
Hulisandra, Indu. “Quantifying Changes in Monarch Butterfly Habitat in California.” PhD diss., (University of Southern California, 2020) https://spatial.usc.edu/wp-content/uploads/formidable/12/Indu-Hulisandra.pdf
Jepsen, Sarina. “Infrastructure bill is a win for bees and butterflies, including monarchs.” Xerces Society for Invertebrate Conservation, 15 November 2021. https://xerces.org/press/infrastructure-bill-is-win-for-bees-and-butterflies-including-monarchs
McCormick, Erin. “Western monarch butterflies are nearly extinct. California has a plan to save them.” The Guardian. June 4, 2021. https://www.theguardian.com/us-news/2021/jun/04/monarch-butterflies-california-conservation-milkweed
Pelton Emma M., Schultz Cheryl B., Jepsen Sarina J., Black Scott Hoffman, Crone Elizabeth E. “Western Monarch Population Plummets: Status, Probable Causes, and Recommended Conservation Actions.” Frontiers in Ecology and Evolution 7, (2019). https://www.frontiersin.org/article/10.3389/fevo.2019.00258
U.S. Forestry Service. “Monarch Butterfly Habitat Needs.” United States Department of Agriculture: U.S. Forestry Service, 2022. https://www.fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/habitat/index.shtml
Xerces Society. “Western Monarch Call to Action.” Xerces Society for Invertebrate Conservation. 2021. https://xerces.org/western-monarch-call-to-action