For a list of flowers suitable for Monarch Butterflies in our area, click here.
The monarch butterfly (Danaus plexippus) evolved to migrate 2000 to 3000 miles annually between breeding and wintering areas. In the spring female monarchs leave the overwintering areas in search of native milkweed plants upon which to lay their eggs. The plants contain a chemical that is toxic to butterfly predators. The larvae are resistant to the toxin and will feed on the leaves of milkweed. The toxin makes the caterpillars, and later the adults, poisonous to predators. Once the new adult butterfly hatches from its chrysalis it will forage on nectar, find a mate, reproduce and die. It takes multiple generations of monarchs for the population to reach the furthermost breeding grounds, breeding at intermediate sites along the way. In the fall, monarchs (the great great grandkids) leave the breeding areas to head to the overwintering sites which include several coastal locations within the Santa Cruz Mountains Bioregion. What’s amazing is that they’ve never been to these sites before, yet know how to find them. The monarchs use the position of the sun, magnetic compass and information stored in their genes to find their way to the overwintering sites. They will not breed until the next spring.
The western monarch butterfly is one of two populations of monarchs separated by the Rocky Mountains. You may be familiar with the larger eastern population that overwinters in Mexico and migrates as far north as eastern Canada during spring and summer. The western population breeds into the Central Valley, the Great Basin, and as far north as the north-western Rocky Mountains during the summer and overwinters along the California coast. Recent research shows that a few also migrate to Arizona and northern Baja, Mexico, allowing for genetic interchange between the two populations.
In the fall, the butterflies are triggered by reduced daylight and temperatures to leave the breeding areas and start their migration to the California coast where the winter weather is mild. They forage on nectar during the migration and arrive at the West Coast starting in October. Butterfly fans can track the migration movements of monarchs in real time via https://www.monarchmilkweedmapper.org.
Upon arriving on the west coast they will roost in groves of native Monterey cypress (Hesperocyparis macrocarpa) and Monterey pine trees (Pinus radiata): as well as the non-native Bluegum Eucalyptus (E. globulus). The overwintering sites provide a microclimate suitable for survival until the next breeding season. Monarchs protect themselves from the elements by roosting in tight clusters on branches and leaves. When temperatures reach 55⁰F the monarchs will become active. Monarch butterflies forage on nectar and water during the day and then return to the grove overnight.
In February to March monarchs will start to mate while still at the coast. After mating, the female will head east and out of our Bioregion to lay her eggs on milkweed plants. Males will follow females. It takes multiple life cycles for the population to reach the northwestern Rocky Mountains.
Western Monarch Butterfly Population is in Dire Straits.
The western monarch population has declined by 99% since 1980. The graph below shows their dramatic decline. Multiple factors are contributing to the decline. Overwintering conditions are critical for the survival of the population. Many overwintering areas have been lost or degraded due to development, fire suppression, and the loss of diseased or over-mature trees. On the breeding grounds and migratory pathways, milkweed and nectar plants have been lost due to land conversion, fragmentation and pesticides. Climate change is also impacting monarchs with severe droughts, wildfires, and storms that kill butterflies and can affect migration timing. Efforts to combat climate change, ban neonicotinoid insecticides, and restore degraded overwintering tree stands are critical to the conservation of the western monarch population.
Western monarch butterflies can be harmed by the presence of milkweed near their overwintering sites. This may seem odd since they are dependent on milkweed during the rest of the year. If milkweed is planted close to the overwintering areas monarchs may lay eggs during the winter, possibly disrupting their breeding and migration sequence. The larvae may not survive due to low temperatures and starvation.
Another threat is the protozoan parasite, Ophryocystis elektroscirrha (OE), which compromises the health of adult and larval monarchs. OE can be transmitted from infected females to offspring or by larvae from parasite spores ingested by feeding on contaminated eggs or milkweed. Historically, monarch migration to wintering grounds would reduce the parasite load as native milkweeds go dormant during the winter and were not historically present on the coast. Thus monarch butterflies did not evolve to breed at overwintering sites. Tropical milkweed (Asclepias curassavica) a winter flowering species that often is planted near the coast has been found to contribute to increased OE parasitism because the plant does not die back. Monarchs with OE infections can have poorly developed wings or may get stuck when emerging from the pupae. OE infected monarchs may not fly well and often have a reduced life span. To read more about Tropical milkweed, visit xerces.org/blog/tropical-milkweed-a-no-grow.
How to Help Our Overwintering Monarchs
1. Create a garden that will favor monarchs and other pollinators. Plant winter flowering plants as nectar sources for monarchs. Also have a water source available for monarchs. This will benefit other pollinators and birds as well. Here is a list of native and non-native plants for over-wintering monarchs.
2. Do not plant any species of milkweed within 5 miles of the coast (www.xerces.org). Do not plant the tropical milkweed (Asclepias curassavica) anywhere.
3. If you are farther than 5 miles inland from the coast, plant the milkweed native to your region. Visit https://www.calflora.org/cgi-bin/specieslist.cgi?namesoup=milkweed&countylist=any&native=t&plantcomm=any&format=photos&orderby=taxon to use Calflora to find your local native milkweed species.
4. Do not use pesticides. Use of neonicotinoid insecticides is especially harmful. Neonicotenoids are a class of insecticides that are toxic to butterflies and to bees. They are systemic, meaning that the toxin is taken up by the leaves or roots and permeates the entire plant including the flowers. Nectar will contain the toxin and can poison butterflies. Don’t buy plants that were commercially grown using these chemicals and don’t spray insecticides on your garden plants. Unfortunately, neonicotinoids are found in many insecticides although you won’t see that word on the label. Instead look for terms such as Imidacloprid, Acetamiprid, or Dinotefuran, or visit the pesticide ingredient database at http://ipm.ucanr.edu/PMG/menu.pesticides.php.
Also very harmful is the organic insecticide, Bacillus thuringiensis (Bt), as it specifically targets butterfly and moth caterpillars. Learn more about Smarter Pest Management via https://xerces.org/sites/default/files/2019-09/19-034_01_Protecting%20Pollinators%20at%20Home_web.pdf.
5. Do your part to protect overwintering sites. If you learn of overwintering sites in jeopardy contact your representative.
6. Educate your family, friends, and neighbors about the risks facing our amazing monarch butterflies.
7. Volunteer your time and energy to work with community groups that are doing restoration projects at existing overwintering sites. On the state level, the California Wildlife Conservation Board has funding available through the Monarch Butterfly and Pollinator Rescue Program to public and private landowners to fund the restoration of monarch overwintering groves.
References
(1) Altizer, S.M., K.O. Oberhauser, and K.A. Geurts. “Transmission of the protozoan parasite, Ophryocystis elektroscirrha, in monarch butterfly populations.” In The Monarch Butterfly: Biology and Conservation,K. Oberhauser and M. Solensky (eds.). Cornell: Cornell University Press, 2004.
(2) American Bird Conservancy, 2020. Read online at https://abcbirds.org/neonics
(3) Katie Hietala-Henschell and Emma Pelton, S.; 17 January 2019. Read online at https://xerces.org/blog/western-monarchs-in-crisis
(4) Malcolm, S. B. (2018). Anthropogenic impacts on mortality and population viability of the monarch butterfly. Ann. Rev. Entomol. 63, 277–302.
(5) Monarch Joint Venture, 2020. MJV Projects: Western Monarchs. Read online at https://monarchjointventure.org/our-work/list/category/western-monarchs
(6) Pelton, E. and Jepsen, S.; 17 January 2019. Read online at https://xerces.org/press/western-monarchs-in-crisis-2019
(7) Pelton, E., S. Jepsen, C. Schultz, C. Fallon, and S. H. Black. 2016. State of the Monarch Butter y Overwintering Sites in California. 40+vi pp. Portland, OR: The Xerces Society for Invertebrate Conservation. Read online at https://xerces.org/sites/default/files/2018-05/16-015_01_XercesSoc_State-of-Monarch-Overwintering-Sites-in-California_web.pdf
(8) Pelton EM, Schultz CB, Jepsen SJ, Black SH and Crone EE (2019) Western Monarch Population Plummets: Status, Probable Causes, and Recommended Conservation Actions. Front. Ecol. Evol. 7:258. doi: 10.3389/fevo.2019.00258
(9) Satterfield, D. A., Villablanca, F. X., Maerz, J. C., and Altizer, S. (2016). Migratory monarchs wintering in California experience low infection risk compared to monarchs breeding year-round on non-native milkweed. Integr. Comp. Biol. 56, 343–352.
(10) Xerces Society, 2020. Smarter Pest Management: Protecting Pollinators at Home. Read online at https://xerces.org/publications/fact-sheets/smarter-pest-management-protecting-pollinators-at-home
(11) Xerces Society, 2020. Understanding Neonicotinoids. Read online at https://xerces.org/pesticides/understanding-neonicotinoids