Monarch Butterflies in Southern California

share

Ron Vanderhoff, Roger’s Gardens and CA Native Plant Society

During the past few years, the plight of the Monarch butterfly has received a large amount of attention. Monarch populations, especially in the Western U.S., are severely reduced from their historic levels and the species is in trouble. Current census information shows the Western population is now less than 1% of what it was as recently as the 1980’s. Fortunately, home gardeners can play an important role in their recovery.


In this article, we will discuss our Western Monarchs and especially those in and around Orange County.

For more information specifically about gardening for Monarchs, milkweed cultivation and what gardeners can do to help, please see our companion article
“Monarchs and Milkweed, What Gardeners Need to Know”.
For more information specifically about gardening for Monarchs, milkweed cultivation and what gardeners can do to help, please see our companion article
“Monarchs and Milkweed, What Gardeners Need to Know”.

Western Monarchs are Different

One often misunderstood aspect of our local Monarchs is their geography. In North America, Monarch butterflies west of the Rocky Mountains are mostly distinct from those occupying the Eastern half of the continent. What you may have learned in school, or may have read about, might not be quite right for “our” Monarchs. Maps and literature showing Monarchs migrating between Canada and Mexico and forming thick masses on trees of an area in Central Mexico are true. But for the most part, those images do not translate to our West coast population.

California Monarchs, more accurately called Western Monarchs, instead migrate over shorter distances. Monarchs West of the Rocky Mountains each Fall move to the coast of California, not Mexico, and aggregate through the winter at a few very specific groves. These groves have been used annually and are scattered along about 600 miles of the California coast and into Northern Baja. Very few of our Monarchs make the trek to the forests of Central Mexico to meet their Eastern counterparts.

Monarchs begin arriving at these coastal California tree groves (often Eucalyptus, but almost any large trees will do) in October, remain through the Winter and begin dispersing to the East and North in search of milkweed by February. During their winter period at these coastal colonies Monarch activity is limited to occasional sunning, a little hydrating and definitely some nectaring on nearby flowers.

These overwintering months are not traditionally a breeding time for Monarchs. They should be at rest during this time. However, the recent abundance of planted, tropical, non-native milkweeds in gardens might be changing this winter non-breeding pattern and maybe also changing their migratory habits. More and more, research appears to show that Western Monarchs seem to be losing their migratory instincts and becoming more resident and non-migratory.

This change in Monarch behavior may be part of the problem that cultivating tropical milkweed in our gardens is causing. We encourage you to get informed about the native vs. non-native milkweed issues by reading our article “Monarchs and Milkweed, What Gardeners Need to Know”

Western Monarchs are Different

One often misunderstood aspect of our local Monarchs is their geography. In North America, Monarch butterflies west of the Rocky Mountains are mostly distinct from those occupying the Eastern half of the continent. What you may have learned in school, or may have read about, might not be quite right for “our” Monarchs. Maps and literature showing Monarchs migrating between Canada and Mexico and forming thick masses on trees of an area in Central Mexico are true. But for the most part, those images do not translate to our West coast population.




California Monarchs, more accurately called Western Monarchs, instead migrate over shorter distances. Monarchs West of the Rocky Mountains each Fall move to the coast of California, not Mexico, and aggregate through the winter at a few very specific groves. These groves have been used annually and are scattered along about 600 miles of the California coast and into Northern Baja. Very few of our Monarchs make the trek to the forests of Central Mexico to meet their Eastern counterparts.

Monarchs begin arriving at these coastal California tree groves (often Eucalyptus, but almost any large trees will do) in October, remain through the Winter and begin dispersing to the East and North in search of milkweed by February. During their winter period at these coastal colonies Monarch activity is limited to occasional sunning, a little hydrating and definitely some nectaring on nearby flowers.




These overwintering months are not traditionally a breeding time for Monarchs. They should be at rest during this time. However, the recent abundance of planted, tropical, non-native milkweeds in gardens might be changing this winter non-breeding pattern and maybe also changing their migratory habits. More and more, research appears to show that Western Monarchs seem to be losing their migratory instincts and becoming more resident and non-migratory.

This change in Monarch behavior may be part of the problem that cultivating tropical milkweed in our gardens is causing. We encourage you to get informed about the native vs. non-native milkweed issues by reading our article “Monarchs and Milkweed, What Gardeners Need to Know”


Counting Overwintering Monarchs

Since the 1970’s a dedicated legion of Monarch biologists and volunteers have annually performed diligent and thorough Monarch counts at each of the hundreds of overwintering sites along the California coast. Each year, around the Thanksgiving holiday, these sites are painstakingly surveyed and each Monarch is counted and recorded, following a set of very strict criteria.

The accumulated results of this annual Thanksgiving Monarch Count are distressing (Western Monarch Count). During the most recent count (2020-2021) a total of only 1,914 Monarch butterflies were counted in all of California, at 261 sites. In Orange County, at our nine overwintering sites only a single overwintering Monarch butterfly was found – one butterfly!

As recently as 1996, Orange County hosted almost 14,000 overwintering Monarchs – and last year one. Similarly, in 1996 the state total for California was a healthy 1,244,460 adult Monarch butterflies – last year the count was 1,914, a 99.8% decline.



Our local Orange County Milkweeds

The decline of Monarchs is not from a single cause, but one important conservation concern is the availability of the butterfly’s sole food, native milkweeds.

Three species of native milkweed grow in the wilds of Orange County. The most prolific is Asclepias fascicularis or narrow-leaved milkweed, followed by Asclepias eriocarpa or Woollypod Milkweed and then by Asclepias californica or California Milkweed. Narrow-leaved Milkweed is the easiest to grow in gardens and the most likely to be offered for sale.

Our local Orange County Milkweeds

The decline of Monarchs is not from a single cause, but one important conservation concern is the availability of the butterfly’s sole food, native milkweeds.

Three species of native milkweed grow in the wilds of Orange County. The most prolific is Asclepias fascicularis or narrow-leaved milkweed, followed by Asclepias eriocarpa or Woollypod Milkweed and then by Asclepias californica or California Milkweed. Narrow-leaved Milkweed is the easiest to grow in gardens and the most likely to be offered for sale.

Narrow-leaved milkweed grows throughout most of California, outside of the deserts and higher mountains. It is our most widespread milkweed species. In Orange County, narrow-leaved Milkweed grows throughout the San Joaquin Hills including Laguna Canyon, the Chino Hills, through the foothills of the Santa Ana Mountains and at other scattered locations.

Woollypod milkweed has a similar distribution in California, although it is more commonly associated with grasslands and situated slightly further from the coast. Its distribution in Orange County is a somewhat more limited and patchy, but it can also be found in the San Joaquin Hills, the Chino Hills and through the lower elevations of the Santa Ana Mountains, generally below about 2,000 feet.

The beautiful California milkweed is even less distributed in our area, being slightly more mountainous in its preferences. In California it is well distributed, but in our area it is uncommon and only found in a few areas of the Santa Ana Mountains, primarily in the Southeastern edge. California Milkweed is the earliest emerging and blooming native species and therefore of special significance to some milkweed conservation efforts. Roger’s Gardens is currently assisting Monarch researchers with information on the local locations and abundance of this species.



In Orange County,
our three native milkweeds are distributed in the following way:
(click maps for more information)

Asclepias fascicularis Asclepias eriocarpa Asclepias californica
Asclepias fascicularis




Asclepias eriocarpa




Asclepias californica


More About our Native Milkweeds

In most of California, native Milkweeds do not naturally grow in the immediate coastal zone, preferring to stay about five miles or so from the ocean. However, in Orange County, narrow-leaved milkweed does occur in a few native stands that are nearer to the ocean, especially in the Laguna Beach area. Because native milkweeds are generally scarce along the immediate coast, conservation experts recommend not planting even native milkweeds in this area. Instead, coastal gardeners can assist overwintering monarchs by providing Fall and Winter nectar sources for the overwintering adults.

All native milkweeds are herbaceous perennials, meaning that they die-down completely during the cool months of the year, persist only as root systems and then arise from the bare ground again in Spring. By summer, the plants are often robust and flowering – and hosting several Monarch larvae.

Conservation experts now specifically recommend gardeners only plant locally native milkweed species in their gardens. Although novice gardeners sometimes believe they might be helping Monarchs by offering milkweed all year, it is not a good decision. Instead, embrace the natural ecology of the butterfly and the relationship between Monarch and milkweeds. Offering milkweed during times of the year when it has not traditionally been available to them will disrupt their normal breeding, feeding and migratory behavior.

For some gardeners not growing milkweed in the winter can be a difficult adjustment and it may seem contrary to their own desire to help. But just as wild ducks and geese at a park will eat breadcrumbs and then remain at that park year-round, so might Monarchs. Offering Monarchs milkweed during the winter and early Spring is contrary to good Monarch conservation.



The Western Monarch and Milkweed Mapper Project

One way that gardeners and those that enjoy the outdoors can help Monarch conservation is by observing and reporting your Monarch butterfly and native milkweed sightings. Citizen scientists play a big role in providing valuable information to the research community know about the abundance, distribution and phenology (lifestage) of these butterflies and host plants. Helping to track and monitor the butterflies and milkweeds is easy and fun, and really helps.

Anytime a Monarch is seen, preferably in a natural or wildland area, it can be documented. Your observation might be a single butterfly or perhaps several. It can be adults, larvae, chrysalids or eggs – all are important to the research community. Just take a photo or two, record a few simple bits of information, like the date, number, location, type of habitat and so on, attach your pictures and save the information to the Western Monarch and Milkweed Mapper website.

In addition to the butterflies, researchers also need to know where our milkweed plants are and how they are doing. After learning to identify our native species, any time you see one or a patch in the wild you can log and report the details. Knowing where, when, which species and how much milkweed is growing in Orange County is critical to Monarch conservation efforts and can only be accomplished with the help of concerned citizens, like yourself.

Current Monarch and Milkweed sightings on the Western Monarch and Milkweed Mapper



To help, just go to the Western Monarch and Milkweed Mapper site (https://www.monarchmilkweedmapper.org/), login and start reporting. If you are already an iNaturalist or Calflora contributor you can submit your observations through those applications as well.

Currently there are over 40,000 milkweed observations and nearly 20,000 Monarch sightings on the Western Monarch Milkweed Mapper, all submitted by passionate volunteers. Orange County has 437 records, of which we are proud to say over 100 are from Roger’s Gardens staff.



What is Roger’s Gardens Doing and What can You Do?

Roger’s Gardens is quite engaged in the Monarch issue, especially its host plant, milkweed.Our Vice President, Ron Vanderhoff, is a well-known native plant botanist and also a director of our local chapter of the CA Native Plant Society. Together, we have mapped over 150 occurrences of native milkweeds in Orange County and we regularly work with the both the local and west coast research community, including the Xerces Society, on various aspect of milkweed status and distribution. Our staff also provide milkweed herbarium collections and hold collection permits from the National Forest Service, the CA Dept of Fish and Wildlife and agencies.

Roger’s Gardens greatest contribution to Monarch conservation is probably in education and horticultural leadership. Three years ago, when we stopped selling tropical milkweed completely, we created quite a stir. We are proud of that decision and encourage others in our industry to follow our lead.

Roger’s Gardens continues to educate local gardeners about the plight of the monarch. We perform this education through numerous seminars, blogs, videos, informational signage, speaking invitations, personal communications with our guests and many other ways. Our staff are also either officers, directors or advisors to various state conservation and plant science organizations, including Calflora, PlantRight, Cal-IPC and CNPS.

Two years ago Roger’s Gardens launched a Milkweed Exchange campaign, to aggressively replace tropical milkweed with native milkweed in gardens. Any homeowner can remove a tropical milkweed from their garden, toss it into a bag and bring it to Roger’s Gardens. We will dispose of it and in exchange, we will give the gardener a FREE locally native milkweed - no charge. We are also very careful to only offer pesticide-free milkweed, and we never sell plants that have been treated with noenicitinoid insecticides.

Gardeners play an important role in Monarch recovery. Thank you for learning and for helping.