Emily Erickson: Researching Monarch Migration Mysteries

by Sarah Van Roo

Wandering the trails and sidewalks of Oakland with a butterfly net over her shoulder, Emily Erickson is clocking about 60 miles a month in search of elusive monarch butterflies. After completing her Entomology doctorate at Penn State, Emily returned to her native California as a post-doctoral researcher on a UC Davis project that has brought her home to Oakland to study the population dynamics of the urban butterfly. She is working on a study of non-migratory local monarch butterflies and their behavior and also seeks to determine whether there is evidence that our urban gardens over space and time influence (positively or negatively) the better-known migratory western monarchs who migrate every year between coastal California and inland breeding sites west of the Rockies.

The iconic monarch butterfly is studied by most schoolchildren as it moves through its four fascinating transformations: from a tiny pinprick of an egg, to a caution-striped caterpillar, to a jewel-like jade green chrysalis, and finally the glorious orange and black butterfly we see darting around our gardens, roads, and farmlands. Less generally understood are this species’ migratory patterns and the evolving understanding of how those are changing. Many of us have a vague understanding of the mythical lore of the monarch migrations, but recently, researchers have noticed emerging non-migratory monarchs in urban gardens around the East Bay. There are other such “resident” populations throughout the world; however, the Bay Area population is relatively new and is rising at the same time that the migratory population has declined dramatically. Erickson hopes to learn more about this resident population and the interactions between the two populations.

In California, handling monarch butterflies is prohibited, including covering, netting, or capturing them, so Emily’s work requires a special permit from the state to tag and sample. She always wears gloves and follows precise sanitary techniques in a focused effort to minimize Ophryocystis elektroscirrha(OE) infections and reduce harm to the butterflies. Many of her repeat sightings have been found within a half-mile range, indicating that they are, indeed, resident monarchs.

Part of her research tests various hypotheses about the effect of OE on resident monarchs, those who have decided to nestle into Oakland as their permanent home and give up life on the road, kind of like the Canada Geese became Oakland Geese. (What is not to love about The Town’s climate?) Questions abound—more bountiful than answers, as it turns out.

• How prevalent is OE in urban gardens?
• Does OE in the population fluctuate over time as the population goes through natural cycles?
• Does OE infection in resident butterflies factor into the sustainability of both migratory and non-migratory populations?
• What is the story on tropical milkweed and its effect on OE infection and migration patterns?

Testing the local monarchs she captures, Erickson has found up to 70% are infected with OE, and 30–50% have a heavy load of the infection, though her data is not finalized. The disease affects flight behavior and reproductive viability, so the question—or one of them—concerns what effect these locals will have on the overall western monarch population, especially those who migrate. As has been reported in the news for the past few years, the monarch population has taken an enormous dive.

This year, however, at least prior to the recent dramatic storms and winds, the monarchs seem to be staging a comeback. Some nearby overwintering sites—Alameda, Oakland’s Ardenwood Farms, Santa Cruz’s Natural Bridges and Lighthouse State Parks, Monterey’s Pacific Grove, Pismo Beach, and others—have all shown monarch resilience this year, with dramatically increased numbers, though still far lower than counts decades ago.

The causes of these annual fluctuations are not totally clear. Weather patterns may have an impact, but the increased use of pesticides and herbicides has certainly been a factor. Much of our native flora habitat has been destroyed by these petrochemicals. Unlike bucolic European highways and byways where wildflowers nod in abundance, our roadway edges are scalped back and sprayed for various reasons, including fire and insect control. These chemicals negatively impact the fragile butterflies, as well as bees and other beneficial insects and fauna.

As more people become aware of this very real monarch crisis—the potential for losing the beloved species entirely—they have sought out ways to help. For a few years, it was thought that plucking the caterpillars from plants and raising them in mesh cages to protect them from predators was a good idea, but this was later discredited as interfering with flight ability and actually increasing OE in the population. Many gardeners and others sought horticultural solutions—what could they plant to help replace all the missing habitat plants and improve the situation?

Planting milkweed is the best overall answer for pollinator health, as it is the primary monarch habitat. Social media horticulture wars rage over the best milkweed variety, and particularly whether the non-native tropical milkweed, is an evil player in this drama. Erickson likes the idea of making gardening and participating in monarch preservation accessible to everyone, not just expert gardeners and entomologists. So, if you already have a little tropical milkweed in your garden, no need to rip it all out, but it is recommended that you cut it back to the ground in winter to help to break the OE cycle. Don’t worry—it is a perennial and will re-emerge! But this cutting can also destroy unseen eggs on the plant, so be sure to check thoroughly for the tiny white dots before cutting it back! Also be aware of seed spread to yards where neighbors may not know to cut back in the winter. Some believe the tropical milkweed interferes with migration patterns. It may be that the plant lures the butterflies into thinking life is pretty good here, and they give up migrating—or perhaps they have already given up travel and just need to nectar here. So, if we have a clear resident population that seems to be becoming permanent, is it undesirable to provide what they like so they have a year-round source of nectar? The answer is complicated.

A primary goal of Emily’s study is to better determine the conservation implications of urban gardens and non-native milkweeds for monarchs in the West, which will help us better understand how best to proceed with Tropical Milkweed. Current consensus, especially while we are still learning about these new resident butterflies, is that a native species—such as Asclepias fascicularis, narrowleaf milkweed—is far and away best choice for monarch habitat, but these are not always easy to find. There is no real standard for labeling native pollinator plants, adding to the confusion for those of us who are guided only by cute garden center cartoons of butterflies or bees. There are specialized nurseries in the Bay Area that focus carefully on natives, so seek out those. Erickson acknowledges that tropical  milkweed is especially popular with home gardeners and is often the easiest variety to find. It is also likely the reason we have resident monarchs in cities, as gardeners enjoy seeing colorful butterflies in their yards throughout the year. However, tropical milkweed—which is evergreen and therefore offers a food source in winter when other native species are dormant—has been associated with increased OE infection and a shift in migratory behavior in the eastern U.S. This is less studied in the west, where monarchs have different migratory behavior.

While Erickson spends much of her time working with non-migratory monarchs in the city, she is also curious about the migratory population. She is currently working on an intriguing citizen-science project led by Dr. Cheryl Schultz at Washington State University-Vancouver to assess monarch distribution and breeding habitat in the spring, when the population is small and stressed from overwintering. The project, known as the Western Monarch Mystery Challenge, asks members of the community to photograph and report any monarchs spied on trails or roads, in gardens or farms, and report the results on its public database. You can participate in the project by sending photos via email to the Western Monarch Milkweed Mapper or the iNaturalist app.

This community-science project is supported by Monarch Joint Venture, the Xerces Society, and the Western Association of Fish and Wildlife Agencies (WAFWA). Data are collected between Valentine’s Day and Earth Day each year. From the photographs, the age of the butterfly can be estimated—the older ones a bit tattered, the younger ones bright and bouncy. This project hopes to also solve a mystery: where do the 60% of monarchs who typically survive winter go during their essential spring breeding period?

As Erickson says—there are way more questions now than answers, but we all yearn for the vibrant health of this beautiful and symbolic creature that evokes transformation and a world without borders.

Lake Merritt resident Sarah Van Roo is a photographer, journalist, and retired attorney who now tends the Bee Hotel Garden at the Gardens at Lake Merritt. She also manages social media for the gardens, including for the hugely successful annual Autumn Lights Festival. For the Splash Pad News, she previously authored articles about the Autumn Lights Festival and a profile of Mary Jo Sutton, head of the volunteer team in the California Native Garden at Splash Pad Park. She reported on the total facelift that transformed the entrance to the Gardens at Lake Merritt.