Due to the additional aspects of the overwintering sites as well as the size of the state of California, updates are provided by three liaisons:  Terry Smith for Northern CA/Bay Area,, Diana Magor for Central CA, and Susie Vanderlip for Southern CA, Please contact them for additional information.


California is the third largest state – nearly 800 miles from the Mexico border to Oregon -  and an important place for the Western Monarch Butterfly population. It provides amazing habitat each winter with over 400 overwintering sites that are home to monarchs migrating from much of the Western states. Each year the Spring migration begins here as monarchs funnel outward across the West in search of pockets of milkweed to lay their eggs, a harbinger of future generations to fill our yards and public lands.

Because of its vast size, contrasting landscape, diverse topography and climate zones, we have many groups involved in monarch conservation including public agencies, advocacy organizations of various sizes and research NGOs. We all work together with one goal in mind: Conservation of the Western Monarch population. Enjoy our updates from around the state.


Northern California | Bay Area & Surrounding

Reported by Terry Smith – Pollinator Posse Co-founder


We’ve been observing unusual Monarch behavior in the Bay Area and surroundings this summer and fall of 2020.  Monarchs have been much more prevalent during the summer months and into the fall than in recent years.  In my own garden, a Monarch Waystation in Oakland, I’ve had visits from multiple adults nectaring and egg laying almost every day since mid-June.  This compares to recent years where I’ve been hard pressed to see eggs or caterpillars before mid-September. 


Beyond my garden, the Pollinator Posse has been fielding an increasing number of inquiries and comments that support this phenomenon.  To try and quantify it, we put out a survey to our members which number close to 1000 mostly in the Bay Area and surroundings, and gathered over 50 responses – a small data set but results were consistent.  We found this has been a widespread phenomenon stretching from San Jose to the North Bay. 


Many folks are noting adults, caterpillars and eggs in greater numbers and more frequently than they’ve observed in the past.  At least some of this can likely be attributed to folks being home more, and in their gardens due to COVID, but that doesn’t begin to account for the extent of the increase. We’re still fielding inquiries daily from folks who report Monarchs in their gardens for the first time in a long time.  Here is the graph of Monarch observations by month we gathered from the responses which matches the flow of inquiries we’ve received.

In addition, we queried people about types of milkweed in their surroundings.  The graph below shows the distribution reported which encouragingly leans toward the native milkweeds – although there are still plenty of the non-natives around.  As of November 1st we started calling for folks to cut back the non-natives.  A number of people are reluctant to do so now because they’re reporting that the plants are covered in caterpillars and eggs.  We know from prior experience that most of the eggs laid at this time of year will lead to unhealthy individuals, but people are still reluctant to cut back.  This is an ongoing challenge in our education and outreach.

One thing COVID has definitely led to is a lot more people rearing caterpillars in their homes.  Over half of our respondents decided to take up Monarch rearing for the first time this year.  We will be increasing our outreach and education about rearing to support the rising interest and try and ensure best practices are being followed. 


Normally the Pollinator Posse would have done many outreach events from spring through fall to raise awareness about issues surrounding pollinators in general and Monarchs in particular.  These would include nursery events, local fairs, school visits, garden tours, and garden group talks to name a few- not  to mention our signature event, Tees for Bees, at local golf courses.  Of course with COVID, none of that happened this year. 


The one event we did engage in was the Autumn Lights Festival – a fall fundraising event which normally takes place in the Gardens at Lake Merritt.  For those of you who attended the WMA Summit in January, you may remember the giant silk Monarch butterflies which were originally created for this event.  Autumn Lights went virtual this year, but our flock of giant butterflies, pollinator plants, and native bees zoomed out in force as you can see below.




Central California

Reported by Diana Magor -  Citizen Scientist

Scott Hennessy of Coral De Tierra, has planted and grown 2 native milkweed species, Asclepias fascicularis (85 plants) and A. eriocarpa, plus bush lupine, black sage and endemic buckwheats in 2000 sq.ft. test plots at Palo Corona Park in Carmel Valley, where the Western Monarch Advocates summit was held last January. Connie Masotti found 8 caterpillars in one of the test plots and some next door at the Carmel middle School. (photo of test plot). Scott has found that irrigation results not only in longer leaf time, but also in wide, lush leaves.

Santa Cruz

Large Monterey Cypress & blue gum Eucalyptus branches fell in the Lighthouse Field overwintering sites this year. Some have been removed from the path beside the sanctuary but 2 of the 3 major Cypress trees are senescing and many beetle infested branches remain on the trees and on the ground. There is a program developed by Xerces, FWS and State Parks to replant Cypress and Eucalyptus in the sanctuary.


Groundswell Ecology Inc. has been contracted to provide both trees and nectar plants for monarchs. Several small Monterey Cypress have been planted as windbreaks on the ocean side of the sanctuary, but are still very small.  The native nectar plants have almost all gone to seed. Fortunately the Eucalyptus have started to flower, and the few monarchs that have shown up there are nectaring from them. There is an effort by some to plant more winter-blooming nectar plants in the vicinity of the overwintering sites.

There has been substantial pruning of Eucalyptus at Moran Lake in consideration of fire danger, so that overwintering site has been partly damaged.


Monarch numbers (these observations provided prior to any Thanksgiving Count results:)  Lighthouse Field. Only 79 monarchs have been counted clustering there to date. John Dayton estimates there are about 265 at Natural Bridges and perhaps 30 at Moran Lake. Some or many of these may have been locally raised. We would normally expect many hundreds to thousands by now at these sites. The high temperatures in the state until a few days ago may have affected the Fall migration, but temperatures have dropped substantially from the 70's & 80's to the 60's since Nov 5, and nighttime temps are now in the high 30's to low 40's. There has been a frost here and in Santa Rosa. We hope that the monarchs being seen in the Bay Area are going to make it to the coast before temperatures drop further into the freezing zone. Pacific Grove. Connie Masotti reports that no monarchs have been seen at the Pacific Grove sanctuary yet.

A survey of monarchs raised by people in the Santa Cruz area estimates that approximately 2,000 have been raised and released between Jan 1 and Nov 5, 2020 by over 100 people. There are probably at least another few hundred being released in the next few weeks.


Oe has been very high this year with all groups I've contacted, some have seen heavier infestations of Tachinid flies than normal and caterpillars are dying from other unknown causes (see below).  Of the 2,000+, approximately 50% have been tested for Oe and only Oe-free or lightly infected adults have been released. This testing practice is being encouraged in the local raising group. There is a nifty little pocket microscope that makes determining if an adult monarch has Oe called the 'Carson Microbrite Plus LED pocket Microscope' which is available from Amazon for less than $14.00 [photo of microscope].

It's entirely possible that the Santa Cruz monarch population will be made up mostly of locally raised monarchs. We have all seen large numbers of adults and eggs in our gardens all Summer and Fall, and are still finding them.

In Santa Rosa, a group that raises there releases only Oe free adults, and of about 300 caterpillars, they have been able to release only about 40 healthy adults. "Black death" was a major problem for them, as it has been for the Santa Cruz group. That term, technically referring to NPV (Nuclear Polyhedrosis Virus), is applied loosely here to caterpillars that just turn black and die before making it to 5th Instar and pupation. One contributing cause in Santa Cruz may have been a "pesticide free" nursery that sprayed with a soap solution in late Aug/early Sept to get rid of Oleander aphids. The nursery rinsed after spraying but much of the solution may have remained on the leaves. The soap solution was associated with many dead caterpillars, and may have been causative. Another issue was the ash that fell on milkweeds in much of California this late August through September from the multiple fires raging throughout the state. Many of us noticed that caterpillars that fed on the ash-covered leaves, even if the leaves were washed with clear water before they fed, hung limply or fell to the ground and did not survive, but that many of the ones feeding on the new growth not covered with ash have survived and are thriving. This is observational and anecdotal, and has not been proven, but is concerning, as it has been reported from raisers in at least 3 different areas.


I suspect the wide-spread use of pesticides is playing a major role in the decline of western monarchs in California. Perhaps raising them in areas that have relatively low-pesticide use, such as Santa Cruz and other coastal towns, may help the Western Monarchs survive until we can get pesticide use down significantly. Arthur Shapiro says that "Monarchs are on life support." Let's work hard to eliminate pesticide use in our neighborhoods and in the farm areas in our state.




Southern California


Many home gardeners in southern California plant to attract monarch butterflies late March thru October. Due to tropical milkweed, the season can continue year-round. It is highly recommended to prune tropical milkweed by mid-October to promote migration and kill off O.e. parasite.


Tropical milkweed remains readily available at Home Depot, Lowes, Armstrong Gardens, and other nurseries. Tropical increases O.e. parasite prevalence and deters migration which concerns many monarch researchers and NGO’s including Xerces and Monarch Joint Venture.


Monarch prevalence varied considerably April thru December 2020. April thru July, there was a profusion of breeding monarchs in Orange County, more than in many years as reported by local monarch butterfly gardeners.

Southern California experienced a “heat dome” in August where temperatures reached up to 112 degrees for three days in a row. Afterwards, a significant reduction in monarchs in Orange County was noted. Some home gardeners reported no monarchs in their gardens after the heat dome.


During October thru November, sightings of monarchs were reported. The Thanksgiving and New Year 2021 count have raised great concern with only 2,000 monarchs in all four hundred plus overwintering sites. One question posed: How much of the overwintering population comes from southern California monarchs? After speaking with researchers, that answer is unknown. Dr. Francis Villablanca of Cal Poly San Luis Obispo who manages tagging of western monarchs stated in his Monarch Alert study that only one monarch tagged from southern California has been found at central coast overwintering sites. He also noted that, in his research, only 1% of all tagged monarchs were found and recorded.


A study from UC Davis in 2015 looked at this question and concluded that southern California monarchs may contribute up to 30%: Monarchs’ Wings Yield Clues to Their Birthplaces | UC Davis: Of the 114 overwintering butterflies sampled, they found that 30 percent developed in California’s southern coastal range, 12 percent in the northern coast and inland range, 16 percent in the central range, and 40 percent in the northern inland range… Across all four overwintering sites, they found butterflies from a wide range of locations, although most were from the southern coast of California and the more distant northern inland U.S.” By Kathy Keatley Garvey on January 26, 2016 in Environment)


In December 2020 and into January 2021, several monarch gardeners in Orange, San Bernardino and San Diego counties reported monarchs ovipositing eggs, larvae on tropical milkweed, and chrysalids in their gardens. Southern California has resident monarch butterflies that do not migrate.

They are able to remain throughout our mild winter months because tropical milkweed abounds in southern California, while native dies back Nov thru March.

Some hopeful insights came from San Diego County on Dec 6, 2020 when Rob Woods reported,

“Hundreds, if not thousands of eggs and caterpillars are being reported by our local monarch butterfly gardeners.” “I believe that this is evidence that while the western migration might be close to a total collapse, there is still a healthy sedentary population here in San Diego County, and perhaps elsewhere.”


Encouraging news.

NOTE: Monarch Joint Venture, Dr. Francis Villablanca, and Xerces question whether resident monarchs are good or bad. It may contribute to the demise of the western migration. It may mean the survival of monarchs in southern California. It may mean a reliance on tropical milkweed and a problematic increase in O.e., decreasing the population. No clear answers are known. Also unknown is where southern California monarchs come from in the spring and where they go in the fall. These questions make it difficult to know how to save the western monarchs.


Regardless, home gardeners are highly encouraged to plant native milkweed and native nectar plants.

Conservation/Research Efforts

There are several Regional Conservation Districts (RCD) in southern California working to protect pollinators and restore habitat, engage, and educate the public, and provide native milkweed seeds and seedlings.

A highly active RCD is the RCD San Diego that is the founding member of the San Diego Pollinator Alliance (SDPA), “a group of organizations and agencies working together to protect pollinators in San Diego County”.

As stated on the RCD San Diego website: The San Diego Pollinator Alliance has developed a series of native demonstration pollinator gardens across the county to give residents ideas on how to create pollinator habitat at home… The SDPA hosts a thriving demonstration pollinator habitat at the San Diego County Fair called the Pollinator Pathway. Other pollinator gardens around San Diego County are also listed as week as a list of other RCD programs and contact info.

Native Milkweed Sources in Southern California


SDPA is working to establish a San Diego seed source of native milkweed that can be used in pollinator habitat projects of all scales – from the home garden to restoration projects.

Visit the Resource Conservation District of San Diego website for more information on plants available for purchase by San Diego residents.


Pollinator Health | Resource Conservation District


On the site are a host of Pollinator Health Resources, Native plant resources, where to buy native milkweed and nectar plants in the San Diego area, and how to plant. For more nectar plant lists on the Xerces Society webpage

Monarch Nectar Plants California.pdf

Additional sources for Native Milkweed and nectar plants in Southern California include:


San Diego County

City Farmers Nursery (City Heights) Walter Anderson Nursery (Poway & Point Loma) Mission Hills Nursery (Mission Hills) Neel’s Nursery (Encinitas) Anderson’s La Costa Nursery (Encinitas) El Plantio Nursery (Escondido) Green Thumb Nursery (San Marcos) Myrtle Creek Nursery (Fallbrook)


Orange County

Tree of Life Nursery (San Juan Capistrano) Back To Natives Nursery (Santa Ana) Fullerton Arboretum (Fullerton) Green Thumb Nursery (Lake Forest)


Riverside County

Parkview Nursery (Riverside) Parkview Nursery (Arlington) Cactus Mart (Morongo Valley)


Los Angeles County

Theodore Payne Foundation (Sun Valley) Artemisia Nursery (Alhambra) Rancho Santa Ana Botanic Garden — Grow Native Nursery (Claremont)


Ventura County

Matilija Nursery (Moorpark)



Videos about the Western Monarch Summit

Help Us Conserve the

Western Monarch

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.

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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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