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Caterpillars of California pipevine swallowtail can safely consume the poisonous plant, which in turn makes the butterflies toxic to predators.
A pipevine swallowtail butterfly is is not listed as a rare butterfly, but pipevines have become less common and in many locations the butterfly is no longer sighted.
Dutchman's pipevine (Arictolochia california) is the larval food of the California pipevine swallowtail butterfly.
Napa Valley has a unique plant growing along its waterways, especially along the Napa River. It is Dutchman’s pipevine (Aristolochia californica) and it is native to California. This plant, one of more than 500 species in the genus, grows only in Northern California and is the larval food of the pipevine swallowtail butterfly.
Pipevine flowers are different from the blooms of other plants. The Dutchman’s pipevine got its name because the flowers look like the pipes smoked in the Netherlands. The flowers appear before the leaves, usually in late February, and have a strange way of being pollinated.
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Some people think the flowers are meat-eaters as they are pollinated by fungus gnats. After a gnat enters the flower, the flower closes. As the gnat moves around inside, it picks up pollen. After three or four days, the flower opens and the gnat moves on to another flower. I discovered this phenomenon when I opened a flower and found a gnat moving around inside.
Once pollinated, the flower produces green fruit with seeds inside. I have collected these seeds and tried to propagate them, but it was difficult. The pipevine grows from rhizomes and is equally hard to reproduce from cuttings.
A few years ago I took 20-plus cuttings and carefully tried to grow roots to share with my fellow Master Gardeners. Out of the 20, only a few developed roots. I tried again, keeping the cuttings very moist as if they were growing along a river. Of the three flats I handled that way, I think I got five cuttings to take.
This winter I will try digging up some of the roots. My motto is “try and try again.”
The plant is a vine with branches that can grow 20 feet long under the right conditions. I saw pipevine once growing along a small waterfall and it covered the entire bank beautifully. And the butterflies were flying around leaving eggs.
The male pipevine swallowtails have a blue lower wing and the females are dark gray. Both are about the same size as a monarch butterfly.
The swallowtail larvae (Battus philenor) eat the pipevine plant because it makes them taste bad to predators. The female lays small orange eggs in a group of eight to 10 so they are easy to find.
For a few weeks of their lives, the larvae graze together and shed their skin as they grow. They take much longer than most butterfly larvae to become pupae. If I move them into the house to mature, I know it is a five-week commitment. I have to clean their droppings out of the container daily and provide fresh food. They are big eaters so I must not forget a day. As they grow from tiny larvae to two inches long, the droppings grow, too, from the size of red pepper flakes to the size of BBs.
Once they are ready to pupate, they take a big dump and go walking. If confined, they go around in circles, but outside they can travel quite a distance. When they find the perfect place, they spin a web to hold them in place and shed their outside skin for the last time. Under that skin is the perfect pupa.
In my experience, monarch pupae take a little over 16 days to become butterflies. Anise swallowtails and pipevine swallowtails have a different timeline. Some of the pupae emerge in a few weeks and start a new generation. Others overwinter as pupae, and in March, when the leaves of pipevine are appearing, the pipevine swallowtails start to come out. The anise swallowtails did not emerge last summer, but they usually appear in late May or June when wild fennel is growing well.
Pipevine takes a few years to establish itself to the point that it can support the butterfly larvae, so be patient. Once established, the butterflies will find it and start depositing their eggs.
Pipevine is toxic to humans and, if ingested, can lead to cancer or kidney failure. In some countries it is still used as a medicine; however, it is illegal for medicinal use in the U.S. The beautiful pipevine swallowtail relies on the toxin to protect itself from predators.
Become a Master Gardener volunteer: UC Master Gardeners of Napa County is now accepting applications for the Class of 2023. Click on the ”Join Us” button at napamg.ucanr.edu to read the informational brochure and register to attend a mandatory information session for applicants. Applications are due before 5 p.m. on Sept. 30.
Free library talk: UC Master Gardeners of Napa County and Napa Library will host a talk on “Controlling Vertebrate Pests in Your Garden” on Thursday, Aug. 4, from 7 to 8 p.m., via Zoom. Learn to identify them and use integrated pest management to protect your bounty.
To receive the Zoom link, register at http://ucanr.edu/VertebratePestsLibraryTalk.
Free guided tree walk: Join UC Master Gardeners of Napa County for a tree walk at Fuller Park in Napa on Tuesday, Aug. 9, from 10 a.m. to noon. Space is limited to 12 people and each person attending must pre-register.
The International Union for Conservation of Nature (IUCN) officially classified monarch butterflies as endangered. The group's red list, which includes over 147,000 species, is used by NGOs, private companies, and global policymakers to inform conservation efforts for threatened and endangered species.
The U.S. Fish and Wildlife Service considered the monarch's status in 2020 and determined that classifying the butterflies as endangered was warranted but that there were higher priorities. The species will be assessed again in 2024 to determine whether it will receive protections under the Endangered Species Act. These protections include the designation of critical habitat—land on which habitat-damaging activity and development by government agencies and private citizens would be prohibited, and the banning of "taking," trapping, or killing the monarchs.
"If nothing else, the process of reviewing monarchs and getting people to talk about their decline and conservation has generated a lot of momentum," said Wendy Caldwell, executive director of the nonprofit Monarch Joint Venture. "We're making a lot of progress there and can continue to do so with or without that [classification]."
Both Eastern and Western monarch populations showed a slight increase during the most recent counts. Western monarchs stay west of the Rocky Mountains and spend winters in Southern California and the Southwest, while Eastern monarchs, whose migration is better-documented, spend winters from Central Mexico to lower Canada.
Although the population uptick sparked hopes of recovery among conservationists, the insect still faces a long road to reaching the population level it held three decades ago when an estimated 700 million made the annual migratory journey. "This is an improvement, but larger numbers are needed to significantly improve the population," Karen Klinger, a GIS specialist examining monarch habitats at the Field Museum in Chicago, told Stacker.
Both populations make a multigenerational journey to breed throughout the summer and return home for the winter. Though intensive, monarch migration is also incredibly delicate, relying on favorable climate conditions and an abundance of the only plant monarch caterpillars eat—milkweed. Shifting landscapes and climate change have contributed to the monarch's long-term decline.
Stacker looked at the decline of Eastern and Western monarch butterfly populations and contextualized the challenges facing the species, citing data from the World Wildlife Fund and the Xerces Society.
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When the Xerces Society first began winter counts of Western monarchs in 1997, it surveyed just over 100 sites along the California coast. Today, its Thanksgiving counts cover over 283 sites in the Southwest and California. Even with the expanded survey range, a Stacker analysis showed that monarch counts declined by 80%. When normalized by the average count seen at every site, the population is nearly half of what it was. Historic droughts, wildfires, and encroaching developments have shrunk overwintering habitats, and pesticide use has impacted breeding areas.
Last winter, monarchs occupied 2.84 hectares of forest habitat in Mexico—a 35% increase from the previous year, but still a significant dip from the counts realized in the 1990s. Insect populations naturally fluctuate with climate conditions. Favorable temperatures and precipitation can be a boon to monarch populations, meaning year-to-year counts can offer a limited scope compared to long-term trends. When looking at population averages, the past five years represented a 68% decline from the 1993-97 time period.
In 2016, the U.S., Canada, and Mexico set a goal to reestablish Eastern monarchs in six hectares of forest in Mexico by 2020, a range that would protect the species from extinction thresholds even with the natural dips in its population. Though the deadline has passed, conservationists are still working toward that goal. A 2017 U.S. Geological Survey report estimated that over 1.3 billion stems of milkweed were needed throughout the Eastern monarch's migration corridor. All but one of the 16 scenarios the USGS developed to reach that goal rely on land from the agriculture, residential, conservation, energy, and transportation sectors. Agriculture is the only sector that has the coverage area to restore the needed milkweed by itself.
Unlike other plants that spread through seeds or runners, milkweed spreads via underground stems called rhizomes. "We probably, through agriculture, expanded the quantity of milkweed just by disturbing the landscape through cultivation," Caldwell said. But changes in agricultural practices, including wider use of pesticides, consolidation of smaller farms, and the introduction of herbicide-resistant, genetically modified crops have reduced the spread of milkweed.
"Those agricultural fields used to be really productive for monarchs. They're not anymore, but we want to bring that back again," Mark Johnston, a GIS analyst with the Field Museum, told Stacker. "There is a big push, at least in our region, to try to get back to sustainable agriculture," he said. This means scaling back heavy conventional production in favor of more diverse crops and avoiding herbicides like glyphosate, which decimate milkweed.
The U.S. Geological Survey has also recommended converting margins of monoculture farms to environmentally diverse habitats under the Conservation Reserve Program. In the application-based system, farmers are paid annual rent to halt agricultural production over a 10-15 year period, instead planting species that can support habitat and improve environmental quality. Such alternatives have different goals, with some focused on mitigating soil erosion or improving water quality and others targeting pollinators and endangered species.
Beyond agriculture, "right-of-way" corridors have also offered an opportunity to support pollinators in non-residential zones. Under an agreement with the U.S. Fish and Wildlife Service, the University of Illinois at Chicago has, since 2017, been partnering with transportation and energy companies to provide monarch habitats on those companies' land in exchange for regulatory easement on other portions of land. Companies participating in the agreement are subject to additional conservation regulations under the Endangered Species Act, and could continue activities that are estimated to have a minimal or temporary impact on monarch habitats.
Eastern monarchs, living anywhere from two to six weeks, make their 3,000-mile journey through a migratory relay race. Traveling 25-30 miles daily, they stop at breeding grounds to lay eggs for the next generation that will continue the trip north. Decreasing day length, temperature fluctuations, and milkweed quality are environmental cues that signal monarchs to delay reproduction and begin their return south. But climate change has made that process more fragile.
"What monarchs need most is well-timed resources," Caldwell said, and what scientists call "phenological mismatch" has become more prevalent. This could be a late freeze killing swaths of milkweed in the South where the first generation of monarchs will stop to breed, or it could be later blooming times that make it harder for monarchs to find nectar—in essence, it is a demonstrable circumstance that alters the timing of a species' life cycle patterns.
The nature of monarchs' multigenerational journey can also amplify climate's impact. In a year where temperature and precipitation are favorable, more caterpillars will survive to complete the next leg, exponentially increasing the number of eggs they'll lay further north and the number of butterflies that will eventually return south.
Even though the agriculture sector has the biggest opportunity to restore milkweed, the USGS emphasized an "all hands on deck" approach that involves planting across rights-of-way, agricultural, and residential sectors.
Klinger, whose work with the Field Museum specializes in examining monarch habitats in metropolitan areas and along rights-of-way, said that the most successful gardens have many blooming flowers and diverse types of milkweed. Some species, like swamp milkweed, are preferred for egg-laying, while others may offer advantages based on seasonal circumstances. It's also important that gardeners plant native milkweed because non-native varieties, such as tropical milkweed, can become invasive.
Regardless of space, Klinger emphasized that many habitats can support monarchs. "We have people monitoring patches of all shapes and sizes, from one or two plants to hundreds of plants in their garden," she said. Through the Field Museum's citizen science monitoring project in the greater Chicago area, they've seen a single potted milkweed support a butterfly's full life cycle. Monarchs have been seen flying as high as 11,000 feet, so even skyscraper gardens can be beneficial. The above photograph, submitted to the project by a participant, shows a milkweed plant covered in caterpillars—evidence that even the most modest footprints can have a significant effect.
Penny Pawl is a UC Master Gardener of Napa County.
Got Garden Questions? Contact the Master Gardener Help Desk. Submit your questions through their diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email. For more information visitnapamg.ucanr.edu.
For the holidays: Get inspiring home and gift ideas – sign up now!
Caterpillars of California pipevine swallowtail can safely consume the poisonous plant, which in turn makes the butterflies toxic to predators.
A pipevine swallowtail butterfly is is not listed as a rare butterfly, but pipevines have become less common and in many locations the butterfly is no longer sighted.
Dutchman's pipevine (Arictolochia california) is the larval food of the California pipevine swallowtail butterfly.
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