Three Myths About the Monarch Butterfly

The beautiful Monarch butterfly – possibly America’s best-known butterfly – is being considered for “endangered”status under the Endangered Species Act. Meanwhile, we’re cutting down the trees these creatures depend on. Nativist myths are partly responsible.

There are two migrations of these butterflies: East of the Rockies, these butterflies migrate between Mexico and the northern part of America. On the Western side, they migrate between the interior and the coast. These are the butterflies we see in California.

The Eastern migration is threatened mainly by a lack of milkweed, their nursery plant, as farmers efficiently exterminate the “weed.” But the Western migration is threatened by something different – a steady reduction in wintering sites as the war on eucalyptus trees continues. On Treasure Island, where Monarchs have been known to over-winter in some years, hundreds if not thousands of trees are being cut down.

We think the article  below is an important one. It’s  republished with permission from “Death of a Million Trees.” Recognizing the truth will help us save these beautiful creatures.

MONARCH MYTHS REVISITED by Million Trees

Debunking the myths of nativism—especially those that justify the eradication of non-native trees—is the task we have assigned ourselves, which requires us to revisit a few of the misconceptions about monarch butterflies in California.

Monarch Butterfly. Creative Commons

Monarch Butterfly. Creative Commons

When application for endangered status for monarchs was filed in August 2014, a few new monarch myths emerged and have since been faithfully repeated by native plant advocates who are demanding the eradication of our urban forests.  The monarch migration in California is using predominantly non-native trees, which should afford those trees some protection.  Unfortunately, it has only produced more convoluted theories that deny the value of non-native plants and trees to monarchs.

Myth #1:  The California migration of monarch butterflies prefers native trees for their winter roost. 

Monarch butterflies roosting in eucalyptus tree.

Monarch butterflies roosting in eucalyptus tree.

A study of the trees used by monarch butterflies for their winter roost in over 300 different sites in California reported that the vast majority of monarchs are using eucalyptus:

“Three types of trees were used most frequently by roosting monarchs:  eucalyptus (75% of the habitats primarily Eucalyptus globulus), pine (20% of the habitats; primarily Pinus radiata), and cypress (16% of the Cupressus macrocarpa).  Twelve other tree species were identified…with a combined prevalence of only 10%.” (1)

Unfortunately, this fact has been obscured by a small study of a few selected sites used by monarchs during their migration.  Griffiths and Villanova (2) observed the monarch migration in a few sites in Monterey and San Luis Obispo counties.  They report that the monarchs moved around among three tree species including eucalyptus, suggesting to them that Monterey pine and cypress are equally important to the monarchs.  While we don’t doubt that this may be true, we don’t think we can generalize from this study because it was conducted in the small native range of Monterey pine and cypress.

The California migration of monarchs spends the winter months roosting in tall trees in 17 counties along the coast of California, from Mendocino County in the north to San Diego County in the south. (1) Most of that expanse is outside the native range of Monterey pine and cypress.  Griffiths and Villanova do not acknowledge that both Monterey pine and cypress are being eradicated outside their native range for the same reason that eucalyptus is being eradicated, i.e., they are considered “alien invaders” where they have been planted outside their native range.  Here in the San Francisco Bay area, for example, 500 Monterey pines were destroyed on the Marin headlands a few years ago and an untold number of Monterey pines will be destroyed by the FEMA projects in addition to those that have already been destroyed here.

If, in fact, monarchs do have a preference for Monterey pines and cypress for their winter roost, they do not have that option outside of the small native range of those trees in Monterey County. 

For the record, we should tell you that we are just as opposed to the pointless destruction of Monterey pine and cypress outside their small native range as we are opposed to the destruction of eucalyptus.

There is paleontological evidence (fossil cones) that Monterey pines lived in the San Francisco Bay Area several times in the distant past.  That finding was reported (4) in Fremontia, the journal of the California Native Plant Society.  The author asked that Monterey pines be allowed to remain where they lived in the past because the species is threatened in its small native range.  Unfortunately, her advice has been ignored by native plant advocates, who continue to demand that all Monterey pines be destroyed where they have been planted outside their present native range.  This extreme viewpoint is one of the reasons why native plant advocates have earned their reputation as fanatics.

Myth #2:  The California migration of monarch butterflies used exclusively native trees before eucalyptus was planted in California.

Those who wish to discount the value of eucalyptus to overwintering monarchs often assume the California monarch migration predates the planting of eucalyptus in California in mid-19th century.  That assumption supports their claim that all of our eucalyptus can be destroyed without having a negative impact on monarch butterflies.   In fact, there is no historical record of the monarch migration until the mid-19th century.  The historical record of the monarch migration was reported by Vane-Wright (3), who tells us the California monarch migration is probably a 19th century expansion of the range of the eastern monarch migration, from east of the Rocky Mountains to Mexico.  Recent molecular analysis of the monarch migration confirms that the eastern and western migration of monarchs in North America are genetically identical, suggesting that the populations might be dispersing east and west from their Mexican winter roost. (5)

Monarch caterpillar on milkweed. Tilden Botanical Garden

Monarch caterpillar on milkweed. Tilden Botanical Garden

Monarch butterflies are not usually eaten by birds because their host plant contains a toxin that makes birds sick and the monarch’s warning colors broadcast that fact.  The warning colors of butterflies that are toxic to birds are often mimicked by other species of butterflies to confer that protection.  There is a monarch mimic, the Viceroy, in the eastern US, which occurs in California only in a tiny bit of riparian habitat in southeast California.  “The lack of mimics suggests the [monarch] may not have been here long enough for any to evolve.” (6)

Myth #3: Non-native species of milkweed is harmful to monarch butterflies.

Monarch butterflies lay their eggs on milkweed and their larvae, the caterpillar, feeds exclusively on milkweed.  Many native plant advocates believe that the monarch requires a native species of milkweed.  They are mistaken in that assumption.  Wikipedia lists over 35 species of milkweed (genus Asclepias) all over the world and many are known to be used by the widely dispersed populations of monarchs.

The dispersal of monarchs from their original range in North America is approximately 200 years old, according to molecular analysis of populations across the Pacific Ocean (Hawaii, Samoa, Fiji, New Caledonia, New Zealand, Australia) and across the Atlantic (Spain, Portugal, Morocco).  These dispersals are assumed to have been aided by human transportation of both milkweeds and monarchs and extreme weather events.  “For example, monarchs were recorded in Australia in 1870 and were most probably carried there on cyclonic winds from a source population in New Caledonia.” (7)  These populations do not migrate and are therefore genetically distinct from the ancestral population of North American monarchs as a result of genetic drift.

In many of the homes of new populations of monarch butterflies there was no native species of milkweed before being introduced simultaneously with the monarch populations.  Although there are numerous members of the milkweed family native to Australia, monarchs do not appear to utilize the native species, preferring the introduced species of milkweed.

Tropical milkweed (Asclepias curassavica) Creative Commons

Tropical milkweed (Asclepias curassavica) Creative Commons

In California, a tropical species of milkweed is popular with gardeners (Asclepias curassavica).  Unlike the native species of milkweed, tropical milkweed does not die back in winter.  Gardeners therefore tend to prefer the tropical milkweed because it makes a colorful contribution to their gardens year around.

Of course, native plant advocates prefer native species of milkweed and they justify their preference by claiming that tropical milkweed is harmful to monarchs.  They claim that the monarch parasite (Ophryocystis elektroscirrha) can accumulate on tropical milkweed because it doesn’t die back during the winter.  Tropical milkweed is the only milkweed available in winter.  The parasite disrupts some winter breeding of monarchs, but that breeding would not occur in the absence of tropical milkweed.  If more monarchs are the goal, tropical milkweed is making a contribution to the monarch population.

New scientific research bebunks the myth that tropical milkweed is harmful to monarchs.  Leiling Tao et.al. (8) studied monarch lifespans when they fed on a variety of milkweed species.  They looked at both resistance to monarch parasite (O. elktroscirrha) infection and tolerance once infected.  They found a complex interaction between species of milkweed the monarchs fed on and the amount of mycorrhizal fungi on the roots of the milkweed.  But one result was clear:  monarchs raised on tropical milkweed (A. curassavica) lived as long, or longer than, monarchs raised on other species of milkweed.  They were less likely to be infected, and once infected, tolerated the infection well.  In short, there is nothing about tropical milkweed as a host that is detrimental to monarch survival in the presence of parasites.

Native plant advocates also speculate that tropical milkweed can disrupt the migratory patterns of monarchs because it is available when native milkweed is not available.  Given that monarchs have persisted for 200 years all over the world, using exclusively non-native milkweed and without migrating, this seems an unnecessarily pessimistic concern.  Neither native milkweed species, nor migration are essential to the survival of monarchs as a species.

Peek under the cover story

As we often do on Million Trees, we have taken a peek under the cover story being used by native plant advocates to justify the eradication of non-native plants and trees.  Once again, we find a lot of pessimistic speculation, but little evidence that eradicating non-native plants will benefit wildlife, or conversely that wildlife can only survive in native habitat.  Yes, it was a tedious journey to that conclusion and we thank you for your patience if you have persevered to our optimistic conclusion that wildlife is far more resourceful and resilient than nativism wishes to believe.

Monarch butterfly in San Francisco. Copyright Janet Kessler

Monarch butterfly in San Francisco. Copyright Janet Kessler


(1) Dennis Frey and Andrew Schaffner, “Spatial and Temporal Pattern of Monarch Overwintering Abundance in Western North America,” in The Monarch Butterfly Biology and Conservation, Cornell University Press, 2004.

(2) Jessica Griffiths and Francis Villablanca, “Managing monarch butterfly overwintering groves:  Making room among the eucalyptus,” California Fish and Game 101(1): 40-50; 2015

(3) Richard Vane-Wright, “The Columbus Hypothesis:  An Explanation for the Dramatic 19th Century Range Expansion of the Monarch Butterfly,” in Biology and Conservation of the Monarch Butterfly,Natural History Museum of Los Angeles County, 1993.

(4) Constance Millar, “Reconsidering the Conservation of Monterey Pine,” Fremontia, Vol. 26, No. 3, July 1998

(5) Justine I. Lyons, et. al., “Lack of genetic differentiation between monarch butterflies with divergent migration destinations,” Molecular Ecology, (2012) 21, 3433-3444

(6) Art Shapiro, Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, California Natural History Guides, UC Press, 2007.

(7) Amanda Pierce, et. al., “Serial founder effects and genetic differentiation during worldwide range expansion of monarch butterflies,” Proceedings of the Royal Society of Britain, 281: 2014.2230.

(8) LeilingTao, et. al., “Disease ecology across soil boundaries:  effects of below-ground fungi on above-ground host—parasite interactions,” Proceedings of Royal Society of Britain, 282: 2015.1993.

Franciscan manzanita is now an endangered species

Last week US Fish & Wildlife announced that Franciscan manzanita is now an endangered species. In 2009 the single plant known to exist in the wild was discovered during the reconstruction of Doyle Drive. It was transplanted to an undisclosed location in the Presidio in San Francisco at a cost of $175,000, (or, according to some accounts, $205,000) including an additional annual cost for maintenance. Is this a preview of potential cost of reintroducing this plant throughout San Francisco?

Franciscan manzanita

Although that plant is thought to be the only one of its species existing in the wild—if the Presidio can be said to be wild—it has always been for sale in nurseries.  Yes, the plant given endangered status is considered the same species as those for sale in nurseries, but it is presumed to be genetically unique.  Because genetic diversity is considered important to the survival of a species, the recently discovered plant has been given endangered status.  This makes for an interesting and puzzling lesson on the Endangered Species Act.

CRITICAL HABITATS FOR ENDANGERED SPECIES

In addition to the conferral of endangered status, US Fish & Wildlife has designated 318 acres of public land in San Francisco as critical habitat for the Franciscan manzanita.    Critical habitats are places where the endangered plant is either known to have existed in the past or they are places that provide what the plant needs to survive.

Five of the eleven places in San Francisco designated as critical habitat are on federal land in the Presidio.  (Details about all the critical habitats are available here.)  Forty of the 318 acres are on private land.  Six of the critical habitats are in 196 acres of San Francisco’s city parks:

  • Corona Heights
  • Twin Peaks
  • Mount Davidson
  • Glen Canyon Park (erroneously called Diamond Heights by US Fish & Wildlife)
  • Bernal Hill Park (erroneously called Bernal Heights by US Fish & Wildlife)
  • Bayview Hill Park

POTENTIAL IMPACTS ON SAN FRANCISCO’S PUBLIC LANDS

The San Francisco Forest Alliance is studying the impact that planting this endangered species might have.  If the proposed critical habitat in these parks is in forested areas, we will undoubtedly object in our public comment because Franciscan manzanita requires full sun which implies that the trees would be destroyed to accommodate the plant.

Sharp Park, Pacifica, CA. Photo by Erica Reder, SF Public Press

We are also concerned about the potential for restrictions on recreational access such as more trail closures and fences needed to protect a fragile, legally protected plant.  The public has had a preview of such loss of recreational assets to protect endangered species at Sharp Park where native plant advocates and their allies have sued to close the golf course, using the Endangered Species Act.

If you are a visitor to or a neighbor of any of these parks, you might want to inform yourself of the potential impact of planting an endangered species with specific horticultural needs.  For example, this is a plant that requires full sun.  Since all of Bayview Hill has been designated as critical habitat and Bayview Hill is heavily forested, you might wonder if this particular park is a good fit for this plant.  Furthermore, this seems to be the only one of the proposed critical habitats in which this plant is not known to have existed historically.

US Fish & Wildlife tells us that the designation of critical habitat for plants does not commit non-federal land owners to reintroduce this endangered plant unless they receive federal funding.  Federal land owners and recipients of federal funding are obligated to consult with US Fish & Wildlife before making any commitments to changes in land use which would not be consistent with the successful reintroduction of the endangered plant.  We assume that the city of San Francisco receives federal funds, so it seems likely that these restrictions would apply to the critical habitats in city parks.  Legal requirements for critical habitat of endangered animals are more rigorous.

MORE INFORMATION AND PUBLIC COMMENT OPPORTUNITY

More information is available from the Sacramento Office of US Fish & Wildlife:

Robert Moler, robert_moler@fws.gov, (916) 414-6606
Sarah Swenty, sarah_swenty@fws.gov, (916) 414-6571

Comments on the proposed critical habitats will be accepted until November 5, 2012. Comments may be submitted online at the Federal eRulemaking Portal at http://www.regulations.gov (Docket Number FWS–R8–ES–2012–0067) or by U.S. mail to:

Public Comments Processing
Attn:  FWS–R8–ES–2012–0067
Division of Policy and Directives Management
U.S. Fish and Wildlife Service
4401 N. Fairfax Drive, MS 2042-PDM
Arlington, VA 22203.