Monarch Butterflies in Virginia

Monarch butterfly
Monarch butterfly
Source: National Park Service

As the human population grows in Virginia, habitat is transformed and wildlife populations are affected. Clearing the forests for agriculture in the 1600-1800's, and the expansion of the suburbs in the 1900's, had the greatest impact. Some species, such as the passenger pigeon, will never be seen again. Others, such as the buffalo, will never reappear in the wild in Virginia. Some, such as the pileated woodpecker, are struggling to survive in habitat that has been fragmented by roads and fields.

Butterflies and moths, however, are likely to survive the transformation of Virginia's natural setting. These insects are able to fly to isolated pockets of habitat, including gardens planted in suburbia intentionally to attract butterflies. The species composition of the butterflies and moths of Virginia has changed as forests were replaced with fields, but future generations of Virginians may be able to enjoy some wildlife right in front yards.

A special effort is underway to save monarch butterflies in Virginia and across North America. The population that migrated from wintering grounds in Mexico to the Northeast declined by 80% after the mid-1990's, dropping to only 200 million in 2018. The population that wintered in Monterey and Pacific Grove, California and migrated into the Pacific Northwest dropped by 98%, from 1.2 million to just 30,000.

In December 2020, the US Fish and Wildlife Service determined that monarch butterflies qualified as a threatened species under the Endangered Species Act of 1973. There was a 10% chance of the main population which migrated to Mexico going extinct in the next 10 years, and a 60-68% chance of the western population migrating to California going extinct within that time.1

Recovery of the monarch is facilitated by people planting native species of milkweed. The caterpillars in the Spring and Summer depend upon milkweed as their food source.

Monarch butterflies transition from eggs to caterpillar, then metamorphose in a chrysalis into a butterfly
Monarch butterflies transition from eggs to caterpillar, then metamorphose in a chrysalis into a butterfly
Source: National Park Service, Monarch Life Cycle

In the Fall, adult monarchs migrate through Virginia and from Virginia to the Gulf Coast before flying to Mexico. Some may choose to spend the winter in South Florida roosts.2

There is no guarantee that the migration will continue. On the West Coast, millions of monarchs used to migrate to overwinter in California at about 400 different sites. Voters approved a bond issue in 1988 to acquire the roosting sites. The California Department of Parks and Recreation, other government landowners, private corporations, and individuals sought to protect the trees from harvest, in contrast to illegal logging in Mexico's overwintering forests.

Excessive tree trimming, new development, and wildfires have damaged or destroyed sites and reduced their capacity to harbor adult butterflies. Drought has killed patches of non-native blue gum eucalyptus which had neared the end of their lifespan, but ha protected monarchs for the last century. Pesticides in milkweed was thought to have affected population numbers, and warming temperatures may have enticed some monarchs to become year-round residents rather than migrate south to warmer winter roosting sites.

In 2018 and 2019 the overwintering populations had dropped to 30,000 monarchs, with the largest number concentrating at Pismo State Beach. Population models suggested the species was at a tipping point, and in 2020 the Xerxes Society estimated the total number of migrating monarchs in California at just 2,000.

Larger populations of non-migrating monarchs may exist in San Francisco and other areas where milkweed is surviving year-round. Those populations keep the species from disappearing on the West Coast. As one professor commented regarding the San Franciso monarchs:3

Maybe they don't need to migrate anymore if it's always warm enough to live here year-round.

in the recent past, West Coast monarchs migrated and overwintered at multiple sites
in the recent past, West Coast monarchs migrated and overwintered at multiple s
Source: Xerces Society, Western Monarch Count

The decline in the overwintering population may be offset by the natural increase in monarch populations during the summer. One female can lay as many as 500 eggs. A 2022 study reported that the summer population had been steady for the last 25 years, suggesting that efforts to expand the number of milkweed plants had not enhanced the natural recovery. According to one of the study's co-authors:4

There's this perception out there that monarch populations are in dire trouble, but we found that's not at all the case... Everybody thinks monarch habitat is being lost left and right, and for some insect species this might be true but not for monarchs... If you think about it, monarch habitat is people habitat. Monarchs are really good at utilizing the landscapes we've created for ourselves. Backyard gardens, pastures, roadsides, ditches, old fields - all of that is monarch habitat.

The study's co-author was aware that populations had declined in the Midwestern breeding range, perhaps because of the herbicide glyphosate being used more widely in corn and soybean fields. In the northern part of that range, however, climate change had improved the habitat and summer breeding populations were increasing. The threat to the survival of the species was during from the southern migration and at the wintering sites, not an absence of milkweed during the summer.

His conclusion was:5

...it's not really a production problem... We don't have fewer monarchs. We have fewer monarchs reaching the wintering colonies.

Links

Monarch caterpillar feeding on milkweed
Monarch caterpillar feeding on milkweed

References

1. "Scientists scramble to learn why monarch butterflies are dying so quickly," UPI, July 22, 2019, https://www.upi.com/Top_News/US/2019/07/22/Scientists-scramble-to-learn-why-monarch-butterflies-are-dying-so-quickly/6961563481223/; "Endangered and Threatened Wildlife and Plants; 12-Month Finding for the Monarch Butterfly," Federal Register notice, US Fish and Wildlife Service, December 17, 2020, https://www.federalregister.gov/documents/2020/12/17/2020-27523/endangered-and-threatened-wildlife-and-plants-12-month-finding-for-the-monarch-butterfly (last checked June 14, 2022)
2. "Like your grandparents, monarch butterflies are now wintering in Florida," Popular Science, January 2, 2019, https://www.popsci.com/monarch-butterflies-winter-destinations-florida/; Hannah B. Vander Zanden, Carol L. Chaffee, Antonio González-Rodríguez, D.T. Tyler Flockhart, D. Ryan Norris, Marta L. Wayne, "Alternate migration strategies of eastern monarch butterflies revealed by stable isotopes," Animal Migration, Volume 5, Issue 1 (January, 2019) https://doi.org/10.1515/ami-2018-0006 (last checked December 25, 2019)
3. "Monarch Population in California Spirals to Another Record Low," Xerxes Society, November 30, 2020, https://xerces.org/blog/monarch-population-in-california-spirals-to-another-record-low; "The Vanishing Butterfly Groves of California," Xerces Society, January 27, 2021, https://xerces.org/blog/vanishing-butterfly-groves-of-california; "Scientists Try to Save Migratory Western Monarch Butterflies as a Mystery Unfolds," KPIX, July 23, 2021, https://sanfrancisco.cbslocal.com/2021/07/23/scientists-try-to-save-migratory-western-monarch-butterflies-as-a-mystery-unfolds/ (last checked July 25, 2021)
4. "Monarch butterfly populations are thriving in North America," UGA Today, June 11, 2022, https://news.uga.edu/monarch-butterfly-populations-are-thriving/; Michael S. Crossley, Timothy D. Meehan, Matthew D. Moran, Jeffrey Glassberg, William E. Snyder, Andrew K. Davis, "Opposing global change drivers counterbalance trends in breeding North American monarch butterflies," Global Change Biology, June 10, 2022, https://doi.org/10.1111/gcb.16282 (last checked June 11, 2022)
5. "Some Monarch Butterfly Populations Are Rising. Is It Enough to Save Them?," New York Times, June 10, 2022, https://www.nytimes.com/2022/06/10/science/monarch-butterflies-mexico.html (last checked June 14, 2022)

plants in the milkweed family, such as Asclepias syriaca, provide toxins to monarch butterflies that protect the adults from predation
plants in the milkweed family, such as Asclepias syriaca, provide toxins to monarch butterflies that protect the adults from predation

monarchs feed on milkweed as caterpillars, and on the nectar/pollen as adults
monarchs feed on milkweed as caterpillars, and on the nectar/pollen as adults
Source: National Park Service, Monarch Butterfly on Milkweed Plant


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