Due to the additional aspects of the overwintering sites as well as the size of the state of California, updates are provided by three liasons:  Susie Vanderlip for Southern CA,, Diana Magor for Central CA, and Tora Rocha for Northern CA, Please contact them for additional information.

My name is Susie Vanderlip,and I have been raising monarch butterflies in my garden in Orange, California for over 10 years and give talks throughout California on monarch butterfly life cycle, butterfly gardening and decline issues over the last seven years.


As a result, I speak to many people raising monarchs, answer many of their questions, and gather data on what others are experiencing raising monarch butterflies in southern California. I share here some of the major issues.


Many people in southern California are eagerly planting milkweed and nectar plants to try  to help save western monarchs. The enthusiasm is alive and well in many homeowners.

1. Prevelance of Tropical Milkweed

There are many microclimates in southern California, most very conducive to raising monarchs and to growing tropical milkweed. I became a Monarch Butterfly Citizen Scientist after O.e. killed many of my newborn monarchs in my 3rd year of raising monarchs (2013). I was only growing tropical milkweed at that time because it was the all I was aware of as I shopped in Home Depot, Lowes and Armstrong Garden Centers – which I shall call the Big 3. I bought and planted it in the ground and in pots.


Since then I have learned about the microscopic parasite O.e. that attaches to monarch butterflies and that monarch caterpillars ingest. Too much O.e. in a caterpillar may result in the birth of deformed butterflies that cannot fly which would cause them to die within a few days from starvation. O.e. accumulates on tropical milkweed leaves and, because tropical continues to leaf out year-round, the O.e. can accumulate to dangerous levels for monarch butterflies. Monarch Health at the Univ of Georgia, where O.e. is studied, concluded that it is critical to prune tropical milkweed to 8” and strip off the leaves every year by Oct. 31st to eliminate the O.e. at the end of every monarch season.

Native milkweed naturally dies back in early November, eliminating the O.e. problem. In early November newly eclosed (emerged) monarchs don’t find any more milkweed and are triggered to migrate to central coast California and overwinter (semi-hibernate for 3 to 4 months). It is thought that migration eliminates the weaker, unhealthy monarchs and is, therefore, good for the overall strength of the population.

It is important then to inform and educate southern Californians who are raising or want to raise monarchs to either plant only native California milkweed or religiously prune tropical milkweed in their gardens by Oct. 31st every year.


Global warming is causing monarchs to return to southern California earlier in March than in past. As a result, milkweed needs to be present for the females to lay eggs on.  Tropical milkweed is leafing out by then though native California milkweed is not.

PROGRESS:  In Jan. 2020, I contacted Altman Specialty Plants which is a primary supplier of tropical milkweed to Home Depot, Lowes and Armstrong Garden Centers (the Big 3) about the need to prune tropical to protect monarch butterflies.  To my delight, they were eager to help and created a tag for the tropical milkweed they sell to the Big 3 that informs buyers to prune the plant by Oct. 31st, encouraging responsible use of tropical milkweed.


Continued education of southern California public about responsible pruning of tropical milkweed is important to raise as many healthy monarch butterflies as possible.

2. Decline in Monarchs

Over the last 4 years, southern Californians raising monarch butterflies consistently report seeing fewer and fewer monarch butterflies March thru October.  They do not show up in the same places every year either.


There are several reasons for the decline. One of the avoidable issues is residential use of pesticides and pesticide use by landscapers for Homeowner Associations (HOA) and cities. It is important to educate homeowners, landscapers, cities and HOA’s in southern California about the damaging effects of glyphosate/RoundUP and neonicotinoids (neonics) which are killing off all pollinators from bees to butterflies. Also educating on the critical nature of pollinators to our food supply, flowers and the beauty in our world.

It is hopeful to share that Home Depot has eliminated 99.9% of the neonic sprayed products. They still sell a few select Citrus sold in CA that must be sprayed with a specific Neonic insecticide in order to be able to sell it due to the Asian Citrus Psyllid.  It is the only known insecticide to control that bug and CA Ag is doing everything they can to prevent the spread. This information was provided by the Home Depot Senior Merchant who purchases for directly for Southern CA, HI, Guam, and Las Vegas and oversees plants being purchased in all states west of the Rockies.

3. Tachinid Flies

The presence of tachinid fly predators in homeowner gardens has increased multi-fold over the last 4 years. The following pattern has been reported by many monarch butterfly gardeners in southern California.

  • First year of a Monarch Butterfly Garden - Many monarch butterfly eggs are laid, many healthy caterpillars, and many new monarchs. Happy new monarch butterfly gardener

  • Second year - Fewer monarchs and signs of tachinid fly predation by mid to late summer and increasing into October. Concerned monarch butterfly gardener

  • Third year and beyond - Tachinid flies are every present and raising monarchs in habitats either outdoors or inside because nearly every caterpillar/chrysalis dies with a white string indicating maggots have been forming inside. Distressed butterfly gardener now buying more and more habitats.

Apparently, tachinid flies were introduced into the western US several years ago for agricultural purposes - to kill insects that attack crops. Unfortunately, they lay their eggs in monarch butterfly larva and chrysalids, killing them. There is no known way to eliminate them. As a result, many home gardeners raise monarchs in butterfly habitats (mesh cages) to protect them from the tachinid flies and be able to rear healthy monarch butterflies. The probability of the monarch surviving from egg to adult outside of a habitat is approximately 5%. With the habitat, the probability can be as high as 95%.

Healthy Habitat Education:  Raising monarchs in habitats does require some health practices on behalf of monarchs. It is important to keep habitats free of frass (monarch poop) daily, cleaning habitats after raising of a butterfly with a 10% bleach to water solution, and other options like cleaning milkweed leaves taken from plants to feed inside habitats. Details on all these practices can be found at links below.

Several Facebook groups of people raising monarchs across the country can provide helpful anecdotal guidance and enjoyable collaboration. Two such Facebook groups are: and The Beautiful Monarch.

Central Coast Loses Over Half of Its Overwintering Monarchs in Big Storm of November 27, 2019.


Santa Cruz. A severe storm the night of Nov 27, 2019, was disastrous for western monarch numbers. In Santa Cruz, it destroyed virtually all of the Natural Bridges 2,000 monarchs. Only 50 were found in a small cluster on a eucalyptus branch the following morning with most of the others dead or dying on the ground. Moran Lake declined from about 400 monarchs to about 50. The Lighthouse Field population, estimated at 3,400 on Nov 27, fared much better than the other 2 sites, losing approximately 800. The Pacific Grove population was reduced from 642 prior to the storm to approximately 316.


That story was repeated all up and down the central coast, including a large population near Big Sur and in the largest population of over 6,700 at Pismo Beach. For more details, see count. Many long term observers said they had never seen destruction like this. The storm was exceptionally bad, as evidenced by the virtual loss of the Natural Bridges colony. The question is why. Climate change? Habitat damage? 

What's a Monarch Cascade?

Kids and adults alike soaking up the magic of a “Monarch Cascade” at Natural Bridges Grove. 

The Lighthouse Field overwintering site consists of some Eucalyptus trees and several Monterey Cypress trees, and is protected from Southerly ocean winds by several rows of Monterey Cypress. Monarchs shelter by hanging under the boughs of the Cypress, which protects them from rain, wind and cold temps at night. The Natural Bridges site had 1 large eucalyptus in the dell where the monarchs clustered, but does not have Cypress in that spot. Where there was once a large Eucalyptus, there is now a a much smaller tree, and I did not observe any monarchs there this winter. They clustered on Eucalyptus branches higher up the hill and off the ground which swing wildly in strong winds and do not appear to provide any protection from the rain. I do not know if this is a significant factor in the loss of the Natural Bridges colony, but an assessment of the NB site and suggestions for improvements are strongly recommended.


Nectaring, Mating Behavior and Spring Migration at Lighthouse Field in Santa Cruz:

John Dayton observed overwintering monarchs nectaring on the sparse Eucalyptus flowers many times between Dec and March. Willows started blooming in late January, but the (non-native) radishes, which are usually a source of nectar, were very sparse and not yet blooming by the time the monarchs were beginning to leave, possibly he suggested, due to the very dry and windy weather we had over January-February. John observed mating late January with most of the females departing by February 18. I saw the first female in my garden 2 miles North of Lighthouse Field on Jan 25.

Monarchs clustering under Monterey cypress bows catch morning sun at Lighthouse Field.

From Feb. 1 on, I have seen between 1 & 5 monarchs in my garden daily, and on March 4, at least 17 monarchs flew through, making 1 pass, then heading North, not stopping to nectar or lay eggs on a large milkweed plant. By Mar. 8, there were only 70 monarchs remaining at Lighthouse Field, mostly males.


John observed 2 females laying eggs the first week of March. A neighbor who has tropical milkweed in his sheltered garden, had monarchs laying eggs there all winter. The caterpillars stripped his plants bare and he gave about 70 away on April 27 to people who had enough milkweed to feed them. The adults did not stay at his property overnight. 

A friend in Sacramento has not seen any monarchs for years, and friends in Dublin, in the East San Francisco Bay area, have not seen monarchs for some time either. They are, however, willing to plant Native milkweeds and nectar plants. A friend in Cameron Park, in the foothills East of Sacramento, reported that he had seen 2 monarchs flying over the golf course adjacent to their property on April 24. 


Tora Rocha of Pollinator Posse, has more information on Monarchs in Northern California and on Waystations.

Pacific Grove

Jimmy Panetta, our Central Coast Congressman, and 4 senators, introduced the Monarch Action, Recovery, and Conservation of Habitat Act ("The Monarch Act 2020") to Congress and the Senate in Feb, 2020. It designates $62.5M for projects to conserve Western Monarchs and another $62.5M for U.S. fish and Wildlife to implement the Western Monarch Butterfly Conservation Plan approved by the Western Association of Fish and Wildlife Agencies in 2019. Funding for both would be split into 5 year amounts of $12,500.


There are 15 milkweeds native to California. The 2 that can sometimes be found for sale in retail garden stores and nurseries now are the Narrow-leaf milkweed, Asclepias fascicularis, and Showy milkweed, Asclepias speciosa. They do take some time to establish, but it’s worth the wait. Other native species, such as Woolypod or Indian milkweed (also California Monarch Milkweed) A. eriocarpa, and Heart Leaf milkweed A. cordifolia, are available in some nurseries specializing in Ca native plants (see links below). Another milkweed that is extremely easy to find in stores is Tropical milkweed, Asclepias curassavica, which is not native, & its cultivation is very controversial (Silky Gold is a cultivar of Tropical Milkweed by the way.) It is native to much of Latin America and the Caribbean, and is not deciduous in warm climates.


Xerces Society for Invertebrate Conservation is adamantly against planting it because 1. it is not native, 2. since it is not deciduous, a monarch protozoan parasite called Oe can build up on the plant over the breeding season and increase the infection which reduces the monarch's flying ability and longevity, and can allow transmission of the spores to its offspring & other healthy monarchs and 3. possibly interfere with their migratory behavior. If you have Tropical milkweed in a garden, it is recommended that you cut the plant to the ground or within a few inches of it every year at the end of October, and continue to trim the new growth back until early January. This largely resolves the latter 2 issues, and at the same time provides clean milkweeds to mated migrating females who start their migration as soon as late January and have no other milkweeds available for egg-laying, since the native deciduous species have not yet emerged.


The other option is to grow it in pots that can be moved inside in a sunny spot, treated with a 5% Clorox bleach solution (regular strength in tap water), followed by 1 or 2 thorough rinses in tap water, and either raised in fine mesh butterfly cages or put outside. [See Frequently Asked Questions. Monarch Disease.] As one of our associates says, it is so well established in Southern California that getting rid of it is unrealistic. 


Encouraged by the WMA 2020 Monarch Summit at Carmel in January, I built my own little waystation in containers on a sunny deck in Santa Cruz, and have received approval for another big one at a housing development in Scotts Valley, 9 miles inland and N of Santa Cruz, to begin shortly. I'm growing nectar plants from seed and giving them to neighbors for their monarch gardens. 

Diana Magor’s container Waystation on her deck in Santa Cruz

Diana would like to hear from anyone who raises monarchs, or who is interested in growing waystations in Central California, or wants to help plant them.

Links to native milkweed and nectar plant growers & suppliers:

  • Las Pilitas Nursery, 3232 Las Pilitas Rd, Santa Margarita, Ca. 934553. San Luis Obispo County So much good information on their website. (Native plants only.)

  • Annie’s Annuals & Perennials, 740 Market Ave., Richmond Ca (East Bay area). 888-266-4370. Amazing Spring and Summer catalogs, with great photos, fun descriptions, growing conditions, and several Ca Native plants.

  • San Lorenzo Garden Center, 235 River Rd, Santa Cruz, Ca. 95060 831-423-0223. Local Santa Cruz garden center with good selection and many pesticide-free plants. (Special orders too)

  • The Garden Company. 2218 Mission St, Santa Cruz, Ca 95060. A. fascicularis sometimes. 831-429-8424. (Environmentally minded)

  • Suncrest Nursery, Watsonville, Ca. Wholesale only.

  • Please check the CNPS website for native milkweed sources near you.

Great Books:


The Monarch, Saving Our Best-Loved Butterfly. Kylee Baumle. 2017 St. Lynns Press. Pittsburg. 

Field Guide to the Butterflies of the San Francisco Bay and Sacramento Valley Regions, Arthur M. Shapiro and Timothy D. Manolos, University of California Press.

Excellent Websites:

  • A wealth of information on invertebrates including the Western Monarch Population.

  • Many fact sheets on all aspects of monarchs.

  • The Monarch Butterfly Garden. Minneapolis, MN 55420.  Instructions, suggestions and contacts on how to do almost anything re: monarchs: a great blog, answers questions, gives gardening tips, resources.

Information to be provided at a later date.


For more information on Northern California, please see contact information above.

Videos about the Western Monarch Summit

The U.S. Fish and Wildlife Service received a petition to list the monarch butterfly under the Endangered Species Act (ESA).  Their decision is due December 2020.

Important Links

WMA provides and updates the information on these pages as a vehicle to encourage people to seek and interact with each other. We make no representation other than that.  This is not a formal "clearing house" where all information is vetted or approved by another organization or government entity.

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