Guest Essay by Kip Hansen — 11 February 2024 — 1800 words/8 minutes

In this essay I continue with a deeper dive into the recent shakeup in the understandings of what is happening with the Monarch Butterfly migrations.  Part 1 covered the topic of the raw numbers of overwintering monarchs at the two roosting sites – the California coastal range and the mountains of Mexico.  Part 2 dealt with overall free living population of monarchs and their relationship to species population of milkweeds.  Both had surprising and counter-consensus findings.

This is the final part of the series, and will cover two remaining points of past common understandings regarding monarchs:

3)  There are a great many advocacy groups oriented to “saving the monarchs” – some are science-oriented and do monarch tracking, counting and tagging.  Some encourage rearing monarchs or gathering and protecting monarch chrysalises until the butterfly emerges. Some encourage planting milkweeds and “butterfly gardens” and supply milkweed plants or seeds.

4)  Commercial enterprises have arisen that mass breed monarchs (and other butterflies) either for scientific purposes (biology or nature classes) or for sale to be released at celebrations such as weddings. [examples, not recommendations:  here and here ]

Up until the last couple of years, everyone agreed that we had to “save the monarchs”.  You could count the Monarch Deniers on one finger, if you could find one.

But then:  Science.  New studies were done, new findings emerged.  See Parts 1 and  2.   Monarch counts at overwintering sites were called into doubt by the California Monarch Rebound of 2021-2022 – there had to be thousands and thousands of monarchs overwintering somewhere where they weren’t getting counted; and if in California, then perhaps in Mexico.  New findings showed no decline in the effective population size of monarchs over the last 75 years. If overwintering counts have fallen by 80%,  how has the effective population size remained constant?   The same for the milkweeds monarchs need to reproduce, despite Roundup.

Naturally, someone notices these counter-consensus findings.

Early this year, along  came “Rethinking Monarchs: Does the Beloved Butterfly Need Our Help?” by Janet Marinelli on  January 15, 2024 in YaleEnvironment360. 

The lede to the article is:

“The Eastern monarch butterfly has long been thought to be in peril, but new studies indicate that its U.S. populations are not in decline. Scientists say the biggest threat the species faces is from well-meaning people who rear the butterflies at home and release them.”

Let me try to sort this out so we can understand what is happening here.  We start out with the information shared in Parts 1 and 2 (links above):  It is quite possible, taking the latest studies into account, that the monarch butterfly and their unlikely but magnificent long-distance migrations are not disappearing and not in any danger of disappearing after all.  Despite all the well-meaning efforts to increase the numbers of milkweed plants, it is quite possible, from the new studies, that the milkweed effective population has not declined either.  Milkweeds may be a local situation, but not a continental one.

So, why does Marinelli claim the helpers, the Friends of the Monarchs,  are the biggest threat?  These advocacy groups urge the planting of milkweed plants, even sticking to native milkweed species to be safe.  That can’t be bad, can it?  

And they are encouraging people to raise and release more monarchs during the summers to help make ”more monarchs”.  That can’t be bad, can it?

And they encourage collecting chrysalises and protecting them from parasitic wasps and then releasing the emerging butterflies.  That can’t be bad, can it?

And the butterfly breeders?  They raise thousands of monarchs, mostly (or many) to be released into the wild to increase the free-breeding monarch population. And to help kids in schools learn the magic of the transformation from caterpillar-to-monarch butterfly and see the new monarch fly off into the wild.     That can’t be bad, can it?

Well, I am not 100% convinced by Marinelli, but there is something to what she says.

The basic underlying reason for her concern is OE.  Yes, yet another acronym. 

“Ophryocystis elektroscirrha (sometimes abbreviated OE or O.e.) is an obligate, neogregarine protozoan parasite that infects monarch (Danaus plexippus) and queen (Danaus gilippus) butterflies. There are no other known hosts. The species was first discovered in Florida, around the late 1960s. Since then, it has been found in every monarch population examined to date, including monarchs sampled in North America, Hawaii, Australia, Cuba, and Central and South America.

Dormant spores occur on the cuticles of butterflies, in between the butterfly‘s scales. They are small, brown or black objects about 1/100th the width of a butterfly scale.

The only currently known way of treating the Ophryocystis parasite is by soaking the host’s eggs in a light bleach solution, which kills the spores that are present on the eggs’ surface.“ [ wiki ]

Monarch Watch has this to say:

“Many of us are distributing Monarch butterflies as a means to excite the public, especially schoolchildren, about the wonders of butterflies, metamorphosis and migration. Unfortunately, there is a good chance that our efforts may be actually harming Monarchs by increasing the frequency of an insidious parasite. We have experienced this parasite in our rearing operations at the Universities of Minnesota and Kansas, and know that we have inadvertently distributed larvae that may have been infected. Since most people that receive Monarchs release them, this is likely to result in a higher frequency of infected butterflies. We have been working for the past year on controlling this parasite, and would like to share our results with you in the hope of preventing further negative effects on an organism that we all view with a sense of awe and wonder. ….  The parasite begins its life cycle as an inactive spore which needs to be eaten by a larva. It multiplies within the larva, and during the last few days of the pupal stage produces new spores that are on butterfly’s scales when it emerges. It is then transferred to the surface of the egg or milkweed during oviposition, and begins a new cycle when it is eaten by the emerging larva.”  

In practice, these means that when breeding multiple generations of monarchs in cages, which are reused over and over,  breeding monarchs by commercial breeders, or in large butterfly world attractions, the parasite will become ubiquitous infecting literally  all the monarchs produced, and when they are released into the wild, they will spread OE to wild populations.    It is generally believed that infection with OE lessens migration success and severe infection causes deformed butterflies that do not survive.    Does this really matter?

Don’t be confused – OE is endemic to all monarch populations worldwide.  It is found everywhere in monarch (or Queen butterfly) populations.  The concern and interest relate to the rate and severity of infection.  The literature is varied on the rates of infection:  The Wiki cites the same paper for both these statements:

“Parasite levels vary between geographical populations ranging from 70% to 3%. This is not the case in laboratory rearing, where after a few generations, all individuals can be infected.”

“The prevalence (proportion of butterflies infected) with O. elektroscirrha [OE] is highly variable and it varies inversely with host migration distances. Non-migratory populations can have an infection rate of up to 70%. 30% of the western migratory population are also infected. Less than 8% of monarchs from the eastern migratory population are heavily infected.”

What can we take away from that? 

1.  Monarchs are prone to infection by OE at varying rates across their range, both in the Northern Hemisphere of America and worldwide. 

2.  OE infection is harmful and can impede migration success of monarchs.

3.  In non-migratory populations, southern California, southern Florida and other parts of the world, OE infections are more common – it may be that if milkweeds which are not killed each winter and replaced in the spring then the parasites spores shed unto the milkweeds remain, build up, and are more likely to infect the next generation.

4.  When professionals or amateurs breed, raise, or “save chrysalises” their equipment and cages can harbor OE spores in large numbers and thus infect literally all monarchs raised in the facility.  Releasing infected monarchs can only add to the problem in the wild.

5.  It is possible for both professionals and amateurs to raise OE-free monarchs and prevent the further spread of infection.   Procedures recommended vary slightly.  Monarch Watch focuses on breeding only butterflies inspected to ensure they are not already infected and thoroughly cleaning all equipment between uses.  An archived page from the Shady Oak Butterfly Farm offers advice on disinfecting monarch eggs before hatching.

There is an interesting paper (Majewska et al. 2022) which found, as we would have expected, that the geologically-denser the population of monarchs,  the greater the rate of OE infection –  a basic crowding function.  Thus, crowded commercial breeding facilities, crowded amateur breeding set-ups, and crowded butterfly gardens (which we have all been repeated encouraged to plant at home and in our municipal parks) may be making OE infection rates higher.

Bottom Lines:

1.  Overall, while monarch populations are subject to boom-and-bust dynamics, monarch butterflies are not under any threat of extinction and listing them as Endangered will not  help or save them in any practical way.

2.  There is some evidence that increasing local availability of milkweeds, particularly native milkweeds will increase local summertime monarch populations – however, this is unlikely to increase the continental-scale population in any significant way nor would it significantly increase numbers of monarchs at overwintering sites.

3.  It appears that there is something wrong with the current practices of Monarch Overwintering Counts, in California and probably also in Mexico.  In order to have accurate counts, it will be necessary to search far wider areas for overwintering roosts and not to continue the current practice of only looking at past locations of roosts.

4.  Professional monarch breeding operations, “butterfly world”-type attractions, and amateurs breeding monarchs should take every reasonable precaution against breeding and releasing OE infected monarchs.  The procedures require extra steps but no expensive equipment or materials.

5.  None of the above are reasons for Monarch advocacy groups to quit doing what they are doing.  Spotting, counting and tagging monarchs are good citizen science.  Collecting eggs and chrysalises for education is a good thing (as long as OE prophylaxis procedures are followed).

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Author’s Comment:

I was glad to find new studies that bring new understandings to this topic.  Long-time readers here know that I am fond of monarchs and have followed their ups and downs for years. 

This series give us a good example of how science is supposed to work.  Researchers feel free to ask new questions – questions that may have answers that run contrary to a field’s the current paradigm.  The research is done and the findings promptly published.  These new findings bring new viewpoints into focus and the field is better off.  Policy recommendations based on the old accepted views can now be modified to better align with the new data.

Imagine if this was the case with Climate Science, PM2.5 science, Dietary Salt Science, Dietary Sugar Science and dozens of other fields and topics with set-in-concrete fixed consensus views. 

Thanks for reading.

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