A small team of industrious volunteers counted 8,270 Viola adunca in the Point Reyes National Seashore last week—and they’re just getting started.
The plant, commonly known as the western dog violet, is a small, delicate wildflower and the sole home plant of the Myrtle’s silverspot, an endangered butterfly whose last surviving territory lies in patches of coastal Marin and southern Sonoma Counties.
In all stages of its brief life—from larva to caterpillar to chrysalis to adulthood—the silverspot is hard to find. Its larvae are tucked beneath the leaves of the violet, its caterpillars are nocturnal, and its butterflies thrive in foggy, windswept areas, often obscured from sight.
Which is why the citizen scientists seeking out the creature are mapping its pretty purple home plant, which grows best in open coastal prairies and grasslands mixed with coastal scrub. The butterflies are now in their caterpillar stage and won’t emerge until early summer.
The project is being coordinated by the Point Reyes National Seashore Association and Tanya Baxter, a Marin County botanist who has worked on other mapping projects with the National Park Service.
The effort is well timed, she said, coming as the Nature Conservancy embarks on a program of targeted conservation grazing ushered in by the landmark settlement that will convert ranchlands on the peninsula into more natural habitats.
The Myrtle’s silverspot is one of several threatened or endangered species monitored annually in the park, but data on it is scarce.
“This is the first real census of Viola adunca out here, and it will give range managers the information they need to time and place grazing in ways that actually expand habitat for the Myrtle’s silverspot,” said Ms. Baxter, who is leading surveys through the end of May.
On their first two days in the field, the volunteers covered about 25 percent of the area that Ms. Baxter intends to map. That range lies on the former F and G ranches, a zone that stretches from Bull Point over to North Beach and down toward the R.C.A. receiving station. It is also where the Nature Conservancy is coordinating its first short-term grazing program with the help of fourth-generation Point Reyes rancher David Evans.
“We decided that to protect the general habitat of the butterfly, from egg to juvenile to adult, the most important thing is to look at where it spends most of its life, which is in and around these violas,” Ms. Baxter said.
Western dog violets grow across a wide range, from Alaska through Canada to California. In some areas, they flourish in forests, and along the coast they thrive in prairies and on bluffs. They reach as tall as 4 to 6 inches, have heart-shaped leaves, and their single flowers emerge from the end of a long stem. In the seashore, they grow conveniently close to the coastal wildflowers whose nectar the Myrtle’s silverspot feeds upon.
“The silverspot tends to like it near the dunes because, as an adult butterfly, it’s looking for nectar plants like Grindelia—gum plant—and Monardella, or coyote mint,” she said.
On Ms. Baxter’s first group foray, Inverness resident Ann Elliott counted about 500 violets in her two-and-a-half-hour shift. “It was just gorgeous out there,” said Ms. Elliott, a member of the Marin chapter of the California Native Plant Society, where Ms. Baxter gave a talk about the project last February. “It was a glorious day, just perfect.”
Ms. Elliott has participated in previous PRNSA events focused on removing invasive dune grass from around Abbotts Lagoon. The butterfly adventure wasn’t nearly as physically taxing, she said. The plant thrives in open areas and is easy to spot from as far as 15 feet away. No need to bend down and strain your back.
The average wingspan of the Myrtle’s silverspot, or Speyeria zerene myrtleae, is just 2.2 inches. The upper surfaces of its wings are golden brown with black spots and lines, while the undersides are brown, orange and tan, with black lines and silver and black spots. Its larvae are dark in color, and the caterpillars have many sharp branching spines on their backs.
The butterfly was listed as endangered in 1992. Though it was formerly found in dunes and bluffs from San Mateo County north to the mouth of the Russian River, populations south of the Golden Gate have been wiped out by urban development.
The citizen surveyors use the Gaia GPS app to map the area they cover. During their searches this month, they came upon a surprise: a cluster of western sheep moth caterpillars, said Cristobal Castañeda Salazar, PRNSA’s volunteer manager.
“We probably saw over 40 of them on just one small plant,” he said. “It was a really exciting find.”
The area they explored is enclosed by ranch fences, so the mapping event gave them a chance to explore part of the park that they hadn’t seen before.
“Looking at it from a distance, it doesn’t seem like there’s a lot going on,” Mr. Castañeda said. “But once you’re in this grassland habitat, you look down, and then there’s just all these incredible species of wildflowers, caterpillars and moths. It’s a unique new opportunity for people who are familiar with the park to see it in a new way.”
There are many gaps in existing research about the size and territory of the Myrtle’s silverspot, and Ms. Baxter’s census will help fill them, Mr. Castañeda said.
“Moving forward, this will be another piece of information that the National Park Service and the Nature Conservancy can refer to as they develop new strategies for conserving and managing this landscape,” he said.
Grazing is necessary to provide the open areas where the western dog violet grows best, keeping away the tall grasses that can crowd it out. And land managers say that cattle are necessary for that grazing, since although the park’s tule elk herds are now free to roam, they haven’t yet expanded into the area where the violets grow.
At the same time, too many cattle tromping around at the wrong time can trample the caterpillars or the vegetative cover that they and the larvae need to protect themselves from predators. Sasha Gennet, who is coordinating the Nature Conservancy’s grazing program, has been conferring with Ms. Baxter about the project to make sure cattle and conservationists don’t bump into one another.
“It’s going to be really helpful for the targeted grazing program to have this updated information about where the butterfly’s host plant is distributed,” Ms. Gennet said. “The timing and density of grazing can work to benefit rather than negatively impact those species.”
The next dog violet mapping survey takes place Saturday, Apr. 25 at 10 a.m. For more information or to volunteer, go to https://ptreyes.org/programs-events/