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In these
last days of summer, monarch butterflies (Danaus plexippus) are finishing their
summer breeding in the temperate areas of the northern United States
and southern Canada.1 In just a few weeks, when fall’s cooler
temperatures begin to arrive and signal the coming of winter, the monarchs will
commence their annual trip south, flying 50 to 100 miles a day to their winter
habitat in the oyamel fir forests of Central Mexico’s Transvolcanic Mountains. (Monarchs
whose spring and summer home is in the western United States will spend the
winter in California).1 During their migration and summer breeding period, monarchs will feed on nectar-producing plants and flowers, but will depend most heavily on a single genus of plants — the milkweeds (Asclepias spp.) — for the continuance of future monarch generations. Just as they have evolved to travel the same route
every year using an internal compass, monarchs also have acquired the instinct
to lay their eggs on milkweed plants.2 But it is not just the
wondrous monarchs that derive such benefits from the milkweed, as humans have
used various Asclepias species for
centuries to improve myriad health conditions.
Traditional Medicinal Uses
among Humans
The name milkweed comes
from the thick, white sap the plants secrete when punctured. Butterfly weed (A. tuberosa), which is referred to as
pleurisy root when just the root is being discussed,3 is the only
milkweed species with clear sap. While the genus Asclepias contains about 130 species,4 monarchs are
thought to feed on just 27 milkweeds native to North America.6 Most species
of milkweed have varying levels of toxicity and have been known to harm some livestock,
including cattle, goats, horses, fowl, and sheep.4
In
humans, milkweed toxicity is usually mild, and, as is common with many
medicinal plants, active chemicals in milkweed are responsible for the plant’s toxic
properties as well as its therapeutic benefits. According to Volume 2 of The Useful
Wild Plants of Texas, the Southeastern and Southwestern United States, the
Southern Plains, and Northern Mexico — a text that dedicates 75 pages to
the milkweeds — “The genus Asclepias,
many species of which occur in Texas, have so many, such varied, and such
significant uses that the genus is one of the most highly valued in this work….
The number of medicinal uses of Asclepias,
including cures and treatments for almost every system of the body, is nothing
short of phenomenal.”
Within
the milkweed sap are steroids called cardenolides, which exhibit cardiotonic
properties that produce many of milkweed’s medicinal properties. Some milkweed
species, such as horsetail milkweed (A. subverticillata), have
high levels of cardenolides, while others, such as showy milkweed (A. speciosa), have lower levels.4
Even within one species, different populations produce varying levels of
cardenolides due to ecological factors. Additionally, the plant part (sap,
leaf, etc.) containing the strongest cardenolide concentration often varies
from species to species.
Although
no clinical research has been conducted on any of the milkweeds mentioned in
this article,6 a few human trials in the 1960s and ’70s studied the
potential asthma-reducing benefits of Indian
ipecac (Tylophora indica),7 which is in the same family as the
milkweeds, the dogbane family (Apocynaceae), and has the synonym of A. asthmatica.8
Milkweeds
have been used externally in numerous traditional medicine practices to treat a
multitude of conditions, including skin ulcers, eczema, tumors, sores and
wounds, leprosy, ringworm, burns, warts (due to its caustic properties), throat
and ear inflammation, rheumatism, and headache.4 Native Americans,
Latin Americans, Indians, and early American settlers used various milkweed
preparations internally and externally. Native Americans particularly relied on
whorled milkweed (A. verticillata) root for snakebites. Additional
internal traditional uses include toothache; heart conditions; fever; headache;
digestive conditions including gas, indigestion, diarrhea, and vomiting; and as
a contraceptive and abortifacient (although the late renowned Southwest
herbalist Michael Moore contested the latter usage, claiming milkweed is strong
enough to cause intense nausea and nothing more).
The
Eclectic physicians of the late 19th and early 20th
centuries used butterfly weed to treat respiratory conditions, particularly
pneumonia. In the pandemic influenzas of the early 1900s, according to a 2006
article in the journal Alternative Complementary Therapy, A. tuberosa was used for “chest pain, lung inflammation, coughing,
and to reduce bronchial symptoms.”6 The Eclectics also used pleurisy
root in a tincture or tea formulation to treat fever in children.9
Daniel
Gagnon, RH (AHG), a medical herbalist and owner of the herbal medicine company Herbs,
Etc., said that he “truly, deeply” knows and uses just two milkweed species: inmortal
(A. asperula) and pleurisy root. Gagnon noted that many American herbalists are familiar with inmortal, an Asclepias species native to the Southwest
United States, from studying the Eclectic texts, including the
1854 King's American Dispensatory (Fleter/Lloyd), the 1922 The
Eclectic Materia Medica, Pharmacology and Therapeutics
(Felter), and the 1915 American Materia Medica, Therapeutics and
Pharmacognosy (Ellingwood). Additionally, herbalists who have
studied with Michael Moore or other teachers who were taught by Moore know and
use inmortal. While he sees these two species largely as medicines
for the inflammation of serous membranes surrounding the lungs, heart, and
intestines, he notes that they have many medicinal uses.
“I know there are many other places where these two roots
have been used, but lungs clearly come to mind when I think of inmortal and pleurisy
root,” said Gagnon (email, July 28, 2013). “I personally have been using inmortal
and pleurisy root in my clinical practice for over 30 years and have never had
a client experience negative effects from these two herbal medicines.”
Gagnon noted that pleurisy root is used in the Herbs, Etc.
formulation called Respiratonic®, which has been on the market for
more than 40 years and consistently ranks in the company’s top-10 products.
“We have old-time wildcrafters that sell us inmortal
root every fall. One of my wildcrafters has been picking inmortal for over 60
years. At this time I don't see that the adoption of these two herbs
by the [conventional] medical profession will occur because of [the] way
they use medicines. This plant/drug/therapy is good for this
problem/disease/condition. One pill/one condition medical doctors are not
trained to think of tissue conditions and working from an energetics point of
view. I believe that herbalists are the ones that are going to keep using
this medicine. So, in effect, I am saying that the use of this plant will
remain relatively insignificant.”
Fellow
herbalist David Winston, RH (AHG) — director of the Herbal Therapeutics
Research Library and President of Herbalist and Alchemist, Inc. — reiterated
American herbalists’ usage of pleurisy root as a tea or tincture, and added
that the sap of common milkweed (A.
syriaca) is occasionally used as a topical treatment for warts. If overdose
of pleurisy root does occur, Winston noted that it can cause nausea, vomiting,
and diarrhea. Overdose of inmortal — which should not be used with cardiac
medications or by people with overt heart disease — may cause nausea and
vomiting as well.
“These
are strong medicines, not tonics, and are, in my opinion, best left to people
who are knowledgeable about their use,” said Winston. “Small amounts of pleurisy
root are relatively safe, especially when used in a larger formula. None of
these should be used internally during pregnancy.”
Milkweed
also has been used extensively for non-medicinal applications. As Useful Wild Plants documents, Native
American and Canadian First Nation tribes — including the Hopi, Kiowa, Zuni,
Blackfoot, Cheyenne, Menominee, and more — used many parts of the milkweed
plant for food and to repel insects.4 They also used milkweed fiber,
found in the plant’s stems and seed pods, to construct bowstrings, fish nets,
baskets, twine, and other products. During World War II, the US government took
a tip from these earlier traditional usages and began subsidizing milkweed
crops for the seed floss’s use as insulation in sleeping bags, helmets,
pillows, and more. Hummingbirds use the seed fiber to build nests, and some
have proposed these tiny birds were the first to discover the insulation properties
of the seeds.4 Despite its rich history as a traditional medicine
and fiber product, milkweed is currently viewed by most farmers and ranchers as
an obnoxious weed.
Importance for Monarchs and
Impact of Milkweed Decline
Importance. Female monarchs lay their eggs on no other plants but milkweeds, and monarch larvae — those
pudgy caterpillars with thin stripes of yellow, black, and white — feed on
almost the entire plant, particularly the leaves and flowers.4 It is
thought that they might choose milkweed partly because the larvae ingest
its cardenolides, store the chemicals in their tissue through metamorphosis and
into their adult life, and thus exhibit toxicity to other animals and birds. When
a bird catches an adult monarch that has fed on milkweed with enough
cardenolides, the butterfly will taste bitter and cause some predator bird species to vomit.4,5
Thereafter, that bird will associate the monarch’s unique colors and patterns
as a warning sign.
Recently,
in 2010, scientists writing in the journal Ecology
Letters proposed that monarchs additionally choose to lay their eggs on
milkweed due to a possible medicinal benefit for their offspring — behavior
they refer to as “trans-generational
medication.”10 A protozoan parasite is known to infect developing
monarch caterpillars by “penetrat[ing] the gut wall” and developing into
harmful parasitic spores that cover the adult butterfly’s body. Previous
studies have found that when monarchs lay their eggs on certain milkweed
species that contain more cardenolides, such as A. curassavica, parasite infection in their young is greatly
reduced. Their study echoed these previous results: “All tested parasite
genotypes produced lower spore loads on monarchs reared on A. curassavica than those reared on A. incarnate. Consequently, infected monarchs reared on A. curassavica had longer life spans
than those reared on A. incarnate.”
Decline. Populations of monarch butterflies are
declining, according to a recent survey conducted by World Wildlife Fund (WWF),
which measured the amount of land typically inhabited by the monarchs each winter.9
WWF found a 59% decrease in colony size from last 2012. While it is generally
accepted that there are many contributing factors to monarchs’ decline, most
experts cite milkweed decline and warming temperatures as the predominant
threats.11,12
“Extreme
climate fluctuations in the US and Canada affect the survival and reproduction
of butterflies,” said Omar Vidal, director general of WWF-Mexico, in an
organization press release.11 “The monarch’s lifecycle depends on
the climatic conditions in the places where they develop. Eggs, larvae and
pupae develop more quickly in milder conditions. Temperatures above 95°F can be
lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic
decrease in hatch rate.”
Milkweed
populations are decreasing largely due to increased usage of herbicides/pesticides
across American farm and cropland, as well as expanding urban development,
according to MonarchLab.org. Planned and controlled removal of milkweed is also
an issue. “It’s unfortunate that the monarch host plant has the
word ‘weed’ in its name, as there are some cities and counties that consider it
a noxious weed, and actively remove the plant.” Additionally, because bees are the major
pollinator of milkweed (butterflies are also pollinators, although to a lesser
degree),4 the decline in bee populations could theoretically be having
an effect on milkweed.
Considering the remarkable existence of the monarch —
the only insects that are known to make an annual migration — a continued
decline in their populations would be a major environmental loss. And the
evident waning of milkweed populations also may impact more than just these
butterflies.
“I would venture to say that we need to protect this plant from
herbicides and its eradication,” said herbalist Gagnon. “Losing this herb would
mean that we would lose two of the best plants for inflammation of the lungs,
heart, and intestines where the serous membranes are seriously compromised. I
do not know of other herbal medicines that work as effectively for that
purpose.”
For more information on monarchs and milkweed, and on how to create your own milkweed habitat to attract monarchs, please see the Monarch Joint Venture website.
—Lindsay
Stafford Mader
References
1. Monarch migration. The Monarch Joint
Venture website. Available here.
Accessed August 2, 2013. 2. Avery L. Losing our monarchs: iconic
monarch butterfly down to the lowest numbers in 20 years. Mongabay.com. July
15, 2013. Available here.
Accessed August 2, 2013. 3. Asclepias
tuberosa L. Herbs of
Commerce, 2nd ed. Silver Spring, MD: American Herbal Products Association; 2000. P. 21. 4. Cheatham
S, Johnston M, Marshall L. The Useful Wild Plants of Texas, the
Southeastern and Southwestern United States, the Southern Plains, and Northern
Mexico. Volume 2. Austin, TX: Useful Wild Plants, Inc; 2000. 5. Interactions with milkweed. Monarch lab
website. University of Minnesota. Available here. Accessed August 2, 2013. 6. Garner-Wizard
M. Re: Herbal Approaches for Treatment of Pandemic Influenza. Abascal K, Yarnell E. Herbal treatments
for pandemic influenza Altern Complement Ther. 2006:214-221. HerbClip. http://cms.herbalgram.org/herbclip/330/review44870.html. 7. PubMed search: Tylophora indica.
Article type “clinical trial” selected. Search performed on August 5, 2013. 8. Asclepias asthmatica.
The Plant List website. Available here.
Accessed August 5, 2013. 9. Oliff H. Re:
Historical Perspective of Botanicals Used by Eclectic Physicians in Pediatrics.
Winston D. The use of botanicals in
eclectic pediatrics J Am Herbalists Guild. 2004;Spring/Summer:59-64. http://cms.herbalgram.org/herbclip/284/review44198.html. 10. Lefevre T, Oliver L, Hunter MD,
de Roode JC. Evidence for trans-generational medication in nature. Ecology
Letters. 2010. doi:
10.1111/j.1461-0248.2010.01537.x 11. Monarch butterfly survey indicates
lowest numbers in 20 years [press release]. Mexico: World Wildlife Fund; March
14, 2013. Available here. Accessed August 2, 2013. 12. Monarch conservation. MonarchLab.org.
Available here. Accessed August 2, 2013. |
