.As Eucalyptus Monarch Grove Ages, Butterflies Face Risks

This past October, Santa Cruz lit up under a cloak of seasonal black and orange—nope, not Halloween. And definitely not the Giants. The monarch butterflies have returned to Santa Cruz.

This year’s numbers are up a few thousand, says veteran Natural Bridges State Park interpreter Martha Nitzberg. Even though it’s early in the season, she estimates there are already about 9,000 monarchs fluttering about their designated preserve, located at the state park. Last year’s population of 3,500 represented an all-time low.

“It’s better now than in a bunch of years. It’s exciting to see so many butterflies so early in the year,” Nitzberg told me last month.

Be that as it may, the number of Natural Bridges’ overwintering butterflies is still down more than 95 percent since 1997, and the Tasmanian blue gum eucalyptus canopy that has sheltered generations of butterflies is falling apart.

Extremely sensitive to changes in weather and habitat, as well as to toxins in the environment, monarchs migrate up and down North America, with thousands coming to the local eucalyptus grove, which is nestled in a small canyon. Eucalyptus trees have small leaves that are thin enough for monarchs to wrap their feet around. For longer than anyone can remember, those trees have also provided the butterflies a convenient food source and a haven during the winter months, like a warm blanket or an umbrella to protect them from the wind and rain. But the blanket at Natural Bridges is becoming worn, frayed, and tired.

Monarch populations at the state park began declining precipitously in 1997, Nitzberg says, which is also when the once-reliable eucalyptus curtain began coming down. “Our grove started losing trees in the early 2000s,” she recalls, with much of the damage during some violent wind storms in the ’90s.

A few years later, pitch canker—a pine tree-killing disease—infected the vast majority of Monterey pine trees at the state park, eliminating the windbreak from the park and putting more strain on the eucalyptus. “Our grove is getting old,” says State Parks volunteer Abby Pulman. “Trees are falling down, and the grove is not as protected.”

For decades, Nitzberg and others pushed to plant more eucalyptus trees around the park to protect monarchs’ overwintering, a debate she’s reticent to rehash. “It’s a touchy subject,” Nitzberg says. “I need to be politically correct.”

The blue gum eucalyptus is officially classified as a “moderate” invasive species, and some groups, like the California Native Plant Society, don’t want any of it at state parks—or pretty much anywhere else for that matter, even to refortify a butterfly grove.

A few months ago, Nitzberg and her colleagues did score a win in the debate, as staffers will be allowed to plant a three-tree windblock of eucalyptus trees to reinforce the grove.

Dan Gluesenkamp, executive director of the California Native Plant Society, used to be a docent at Natural Bridges, and remembers the situation being complicated. Gluesenkamp, who later managed a monarch grove at Stinson Beach in Marin County, says that although their size may seem like an advantage, eucalyptus trees can actually grow too tall and block out the sun, which butterflies need in order to thermoregulate.

Brett Hall, vice president of the Sacramento-based nonprofit, adds in a follow-up email that it’s impossible to know all of the factors at play. “Monarchs have been crashing everywhere, from other reasons beyond the degradation of the euc grove,” he writes.

Also, even a healthy grove of eucalyptus trees would not protect monarchs from a more existential threat: a parasite called Ophryocystis elektroscirrha, or “OE,” as it is known among butterfly enthusiasts. OE weakens the insects, often leaving them deformed and unable to fly as far or as long as healthy butterflies.

Scientists estimate that OE has infected 30 percent of the western migratory population.

It’s the latest crisis to strike an already battered species, and the situation on the Central Coast is serious. Once butterflies are infected, they do not recover. The Xerces Society, a butterfly advocacy group, is monitoring its spread.

And local gardeners may be making the situation worse. Nitzberg says that many Santa Cruzans believe they are helping the monarchs by planting milkweed in their coastal gardens to feed monarchs, and the trend began with the noblest of intentions. After all, the milkweed plant provides all of the nourishment a monarch needs to transform from caterpillar into butterfly. Milkweed plants were even sold at the Natural Bridges Migration Festivals for years. Attendees were encouraged to buy $1 plants to “save the monarchs” and plant milkweed in their yards to create “butterfly corridors.”

But the overly abundant milkweed has turned into a host for OE. These days, park workers don’t sell plants, and they discourage anyone within five miles of the coast from planting milkweed, because plants closer to the ocean are particularly susceptible. The flowery plant also disrupts monarchs’ iconic annual migration, when there’s too much of it, leaving them stuck in Santa Cruz year round eating the OE-infested plant grub.

If milkweed proliferates in the monarch wintering grounds, many butterflies won’t migrate at all. The butterflies will lay their eggs year round in Santa Cruz, overstaying their welcome.

Nitzberg discovered a large number of caterpillars this past summer in Santa Cruz County, and she’s begun questioning the status of the entire monarch migration.

“We don’t want them to hang in Santa Cruz for the summer,” she says. “They need to leave for the summer.”


  1. The OE parasite is not “the latest crisis to strike an already battered species”. OE is found in all migratory monarch populations worldwide and has co-existed with the butterflies for thousands of years. While the parasite did infect 30 percent of the western migratory population in the 1980’s and 1990’s the infection rate dropped to between 6 – 16% in the 2000’s and 2010’s: http://imagizer.imageshack.us/a/img924/1535/G7qqvw.jpg With regard to the tree fall problem at Natural Bridges State Park it has been limited to some red gum eucalyptus trees and the vast majority (90%) of monarch overwintering groves are composed of much more durable and self-regenerating blue gum eucalyptus, hence grove senescence is not a significant issue or threat.

  2. According to this article in the Good Times, https://goodtimes.sc/santa-cruz-news/eucalyptus-grove-monarch-butterflies/ I just found out that I was harming Monarch Butterflies by growing an Organic Butterfly Garden that is also a Certified Monarch Waystation… Imagine my Shock!

    I have been growing an organic Butterfly Garden for over six years and in the past five years I have also been hand raising Monarch butterflies indoors in my sun room. I have released hundreds of Monarch butterflies and I have learned so much about the challenges of this most delicate of species. In nature only 3% of eggs laid make it to adulthood. 

    My Monarch raising this year started in mid March, in the past it has started as early as mid February. The first group was very small, just five or six. They emerged and then hung out in the garden. The next generation was much, much larger, I had well over sixty chrysalis and about 95% success for emerged butterflies. I was really concerned though, I thought I would have more eggs than I had milkweed for since that group of sixty plus completely devoured most of my milkweed, but instead of tons of eggs, I didn’t find more than ten, so I figured since it was so early in the year, they must have headed out of town to join the Western migration. For the rest of the summer I had constantly ten Monarchs eggs per generation on their journey from caterpillar to butterfly, until the later generation, then the numbers went up again, not quite to over sixty, closer to fifty, and I have still have half a dozen chrysalis, and a dozen of caterpillars in various stages. Monarchs are flying daily in the garden.

    I have five types of milkweed – swamp, narrow leaf, showy, balloon and tropical, I don’t grow common milkweed in consideration for my neighbors as that variety is highly invasive. As far as success this year it has been consistently 95% that make it from egg to adult, those odds are significantly better than in the wild. 

    And yet according to this article this is a bad thing. How? I mean specifically, exactly how? This quote “DWINDLING MONARCH POPULATIONS FACE ADDITIONAL THREATS FROM A NEW PARASITE AND EVEN SOME WELL-INTENTIONED GARDENERS” is wildly inaccurate, the OE parasite has been around for a very long time. More and more gardeners are becoming aware that Tropical Milkweed needs to be cut back in the winter, and in the microclimate where I live I have never had to to that, I get a couple weeks of frost every winter that will kill any lingeringTropical milkweeds. The perennial milkweeds that I grow, already have died back by the end of fall.

    Let me break this down further… First of all this article doesn’t include any recent reports or research, it is basically an interview with one person, Martha Nitzberg, a park “interpreter” I am not exactly sure what that is, but she is in the Natural Bridges Park, one of the Monarch sanctuaries here on the west coast and she most likely loves butterflies, no doubt. But, still this is one person’s perspective, I do not see any evidence of the claims in this article, such as the “Monarchs are being devastated” The claim is 30% have the OE parasite. Please show me a current report that has data to support this claim, is it this year, last year, in California, in Santa Cruz? One article I found showing this data of 30% infected was from 2004. And what about the Monarchs that have been devastated due to Round Up poisoning (fact… Round up is a variant of Agent Orange). How many… 10%, 50%, 70%? We don’t really know because we don’t focus on that aspect of the decline of not only butterflies, but bees as well. Okay, moving on. In my personal experience of raising Monarchs, this year I had zero, yes zero O.E. infected Monarchs. I know the symptoms well, I have previously lost a few Monarchs to that parasite, nor did I have any NPV (Nuclear Polyhedrosis Virus) incidences, nor Tachinid flies. I lost the 5% of Monarchs I raised to the extreme heat this year (dehydration), to predators (wasps) and to accidents. 

    Next point, the “loss of the Migration” I have studied this too, as I am also concerned. Yet as I said earlier my March Monarchs did not lay eggs in mass here in East Side Santa Cruz, I also asked gardeners close by and going up to Davenport, no, there were not mass eggs anywhere, so where did my sixty plus butterflies go? My theory is that they joined the Western Migration. It is interpreter, Martha Nitzberg’s theory that they are “trapped” in Santa Cruz. Even though I didn’t see hordes of butterflies but a modest ten or so throughout the summer, both are theories and until and unless we tag the butterflies to see where they go, we don’t know for sure. Again we need evidence, studies and real data not just theories and that is on both sides. Next year I plan to tag my early Spring butterflies just to see where they end up. 

    There are some areas like Florida that do have Monarchs year around, that is not a bad thing nor does it appear to stop them from migrating to Mexico, this year has seen a significant increase of migrating butterflies in Mexico – https://www.facebook.com/MonarchButterflyGarden/posts/1485560674814928  (Note: the eastern migration goes to Mexico, the western migration comes here to coastal California) The same issue applies to Florida as it does to south Texas and Southern California, if Tropical milkweed isn’t cut back to encourage new growth, or rinsed off the OE parasite can thrive. Even still the Monarch population in those areas is quite small compared to the larger migration that goes to Mexico. The Monarchs in those areas would still stay there with or without gardeners, milkweed has a vigorous habit of reseeding without the help of “well-intentioned” gardeners.

    Just the “Facts” Ma’am…

    This is one of the many articles addressing the use of the now vilified Tropical Milkweed (by the way, fact… Tropical Milkweed is  classified as a California Native by the USDA . Asclepias curassavica L.  bloodflower native to California, Texas, Tennessee and Florida. Reference – https://plants.usda.gov/core/profile?symbol=ASCU

    This  article (link- http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16499) is an interview in 2015 with Art Shapiro distinguished professor of evolution and ecology, after observing the mating habits of Monarchs in the Bay Area for many years, this is his response to the OE parasite:
    Quote: The reference to OE is correct, Shapiro said. “However, there is an easy ‘fix’ that nobody talks about for some reason: just cut the plants to the ground a few times a year. This will encourage new growth, which will be cleaner, prettier, more nutritious, and uncontaminated with OE. There is nothing inherently ‘bad’ about winter breeding if it’s clean. Infected winter breeding is a population sink. The animals are often too feeble to fly, and may be unable to expand their wings. But perfectly healthy ones are being produced right now in the East Bay on clean plants.” (my side note, I didn’t have to cut my plants back this year, the caterpillars did that for me by devoring them to the nub, nature always takes care of the details!)

    More references about Monarchs and milkweeds –  http://www.livemonarch.com/propaganda.htm 
    Info from a person (one of my mentors) raising Monarchs for the Eastern Migration for over 30 years – https://monarchbutterflygarden.net/is-tropical-milkweed-killing-monarch-butterflies/

    Why am I responding? Because unless you are part of the solution, like I aspire to be, growing an organic garden to support our pollinators and going so far as to have extensive raising environments in my home, tediously rinsing off the milkweeds to give to the caterpillars (which will cleanse the milkweed of the OE parasite), cleaning up the caterpillar frass (poo) to avoid disease, checking in daily to the health and well being of the caterpillars, providing a safe place to pupate, and the after all is done, gingerly collecting the now emerged butterfly to release it back into an organic garden filled with nectar flowers and with countless other butterfly species, you only have these articles that spring every now and then to go by. These articles claim that we gardeners in Santa Cruz (some that I have met actually test the butterflies they rear constantly for OE) are doing great disservice to the very creatures we devote endless time and resources to protect and support and when a friend shows up at my door upset that by growing milkweed that I gave her she is some how at fault… I MUST SPEAK UP.

    And in the future, please back up your articles with some factual resources, I have provided just a fraction of the multitude of resources I have and at any point I can provide many more. We all have opinions on the things we care about, but experience and data can also support (or not) the opinions we have. 

    Bottomline, I feel that I have helped a species towards recovery from the brink of extinction and at the same time I have gained a personal interconnection with the most marvelous of creatures, the Monarch butterfly. When I hold each one on my hand as I release them to their freedom, I feel their trust, their connection that we made in their caterpillar state (there is scientific evidence to this as well), then they fly away, some have come back to my garden and others went on to another adventure. In my five years of experience, this HAS ALWAYS BEEN A GOOD THING! This experience has touched me to my very deepest depths and has healed my deepest emotional wounds like nothing else has. Every newly emerged butterfly is a miracle yet again. These days we need all the miracles we can get (or raise!)

      • Thank you Paul, that is great news, I think the statistics I found were also outdated.

        I am still raising Monarchs, which is about the norm for Santa Cruz this time of year. I have eight large caterpillars, eight smaller ones, two chrysalis, and we released a male Monarch today. None of them had O.E. all are healthy and big! Most of my milkweed is gone, I think I have enough for the caterpillars I have now. I noticed a very large male in our garden before releasing the new one so we took him away from the garden to release. The males are territorial and aggressive so my new males are always released away from my “territory”

      • Hi Paul,

        This story was first inspired by a comment you left on previous story we wrote about the monarchs.

        We tried repeatedly to reach you for this story. While I value this critique you provide in hindsight, I very much wish you had instead responded to our messages. It could have made for a better article.

    • Do you have any thoughts about Monarchs overwintering in other parts of Santa Cruz besides Natural Bridges? I am concerned about all the eucalyptus trees along the rail corridor being cut down.

    • To know if your milkweed is infected you need to look at it under a microscope (and of course know what you are looking for). Or you can rinse the milkweeds off with a mild solution of bleach (10% max) and many say just regular tap water (that also has chlorine in it) is enough. I have rinsed all of my milkweed with tap water this year, I have had zero incidences of O.E. In previous years I wasn’t so diligent with rinsing the milkweed and I did loose a few of the Monarchs I hand raised to O.E. It is very obvious when a Monarch is infected and euthanizing it right away, even though it is sad is best for the overall population. I put the affected Monarchs in my freezer, it is a quick solution and since they are cold blooded, hopefully painless.

  3. Are you available to answer a few questions about Monarchs? It sounds like you have done a lot of reading. I need access to more and better resources. I am raising a few monarchs from my garden for release.

    • Are you are referring to me, not sure… But however, if you want to connect with me, I have been raising Monarchs for over six years, I am a certified Monarch Waystation and this year was the best ever. I lost one to disease, a few to accidents, (they were in the wrong place or the environment was a bit too wet and I was unaware) I have had a 98% success rate from egg to adult, in nature it is 5% or less. You can contact me at my website – http://grantstgarden.dreamdancerdesign.net/contact-2/

      I am happy to answer any questions and I can provide milkweed seeds, and /or butterfly nectar seeds for free.


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