Are California’s Butterflies in Trouble?

“ Butterflies of California ” display at the Bohart Museum of Entomology in Davis, California

Butterflies of California” display at the Bohart Museum of Entomology in Davis, California



On a warm April morning, Arthur Shapiro and I pulled up to the entrance to Gates Canyon. After an unusually rainy spring, the sun was finally shining in the Sacramento Valley.

The Vaca hills, part of the California Coast Range, rose up around us. They were a brilliant shade of green, reminiscent of Ireland, from the fifty inches of winter rains that had fallen so far this wet season. We were there to count butterflies just as Shapiro has done for the past 35 years.

Arthur Shapiro, a biologist and professor at the University of California, spends nearly two-thirds of his days counting California butterflies. Whenever he is not teaching or in the lab, he is out in the field collecting data. Before we were even out of the car, Shapiro called out “There’s my first butterfly of the day- Battus philenor!” Then he translated: he had spotted a Pipevine Swallowtail.

His butterfly dataset is tied with the UK Butterfly Monitoring Scheme, as the longest running butterfly dataset in the world. But lately, his field visits have been different. He has been watching his butterfly count take a nosedive.

Arthur Shapiro scans for butterflies on his Gates Canyon transect in Vacaville

Arthur Shapiro scans for butterflies on his Gates Canyon transect in Vacaville

 Shapiro is not the only one who observed a terrible butterfly season last year. Western Monarch butterflies made national headlines after the Xerces Society released the results of their annual Western Monarch Thanksgiving Count, which documented catastrophic collapse in their population. The numbers in California were at an “all-time low of 28,429 at 213 sites, a decline of 86% since last year’s count, and 99.4% since the 1980s. Experts warned they could completely disappear.

Peter Oboyski, collections manager at the Essig Museum of Entomology, says that because the monarch butterfly is so charismatic and conspicuous, it serves as a good indicator of what’s happening in the environment and to other species. “To think that such an abundant conspicuous species could be so imperiled is really a warning call. What about all the species that are not so conspicuous and not so abundant. What’s happening to them? So it’s kind of a canary in the coal mine,” says Oboyski.

“We’re going to go three miles up and three miles down. So be prepared,” Shapiro told me, eyeing the unwieldy amount of camera gear I was unloading from my car. To Shapiro “prepared” meant bringing only himself, a notebook and pencil. After the tripod and camera were set up, we headed up the canyon following Alamo Creek, scanning the landscape for butterflies.

Shapiro has been walking the Gates Canyon transect for decades and knows it like the back of his hand. It is one of ten butterfly monitoring sites he carefully selected along the I-80 corridor. His sites represent a broad diversity of California ecosystems; ranging from the Suisun Marsh in the central valley floor to 9,000 feet high in the Sierra Nevada at Castle Peak. The Gate’s Canyon site tops out at around 600 feet.

Green-veined White ( Pieris napi).  This egg laying female was visiting Saxifrage.

Green-veined White (Pieris napi). This egg laying female was visiting Saxifrage.

“I picked this site because the vegetation is so rich and that’s reflected in the butterfly fauna,” says Shapiro.  The entrance to the canyon is primarily agricultural land but changes throughout the canyon. Shapiro demonstrated his intimate knowledge of the plants, describing them as we walked. In the lower canyon, naturalized Mediterranean annuals overwhelmingly dominate the grasslands, he says. Shapiro pointed out annual vetch, an important nectar source and several varieties of wild mustard and wild radishes.

“I subscribe to the notion that novel ecosystems are coming into being right under our noses as a result of the interaction of native and introduced species and I find the process exceedingly interesting from an evolutionary and ecological standpoint,” says Shapiro.

Last year was the worst year on record for butterflies at Shapiro’s sites. Monarch butterflies, caterpillars and chrysalis’ completely vanished. Other butterfly species numbers were down as well. “It was like going to a family reunion, and then everyone you’re expecting to see doesn’t show up,” says Shapiro. So far, he says, this spring has been even worse at his low elevation sites.

 The hiking pace for the day turned out to be “butterfly speed.” Shapiro sauntered along, stopping every few feet to observe, call out butterfly sightings and record the findings in his notebook.

As we made our way up the canyon, we arrived at a patch of wildflowers blooming on a south-facing slope. “Boy, there’s very little out. This should be hopping this time of year. It’s a beautiful day, but there’s very little flying,” says Shapiro. The hillside was a nectar jackpot for butterflies: purple and white Lupins, lavender Blue Dicks’ and Ithurial’s Spears and orange Bush Monkeyflower.

“So far has been the worst spring at low elevation,” says Shapiro. His higher elevation sites remain covered in snow so it will be a while before he has a clear picture of how the butterflies are doing at those locations. Shapiro says we do not know why because the data just is not available. “Everything is scarce. Numbers of individuals of everything are way below average. So make of it what you will” he says.

“The challenge is finding the supporting data. These anecdotes are very tantalizing, they give us a sense that there is something very large looming out there. But until we can back it up with quantifiable evidence that’s collected in a systematic way it makes it very difficult to really understand what’s happening.

Amid the tales of decline in populations, this year saw a significant jump in Painted Lady populations. The unusually wet winter allowed their populations to make a significant recovery this year. But Shapiro is not impressed. He is more interested in the overall trend of his observations and says we should see a diversity of species. As we walked, he spotted one crossing our path and called out “Painted Lady. Boooring!”

Many theories have been suggested to explain the decline in butterfly populations. Some theories include changes in agricultural practices, disease, predators, habitat loss, changes in host plants and climate change. Oboyski says “there’s a lot of possibilities to sort through and we haven’t quite pinpointed it yet.”

Shapiro is not convinced that we are getting any closer to solving the puzzle. “As is usually the case the explanations are probably wrong. And the question is what is really going on here?”



Sara Orange-Tip   Anthocharis sara

Sara Orange-Tip

Anthocharis sara

Silvery Blue   Glaucopsyche lygdamus

Silvery Blue

Glaucopsyche lygdamus

Pipevine Swallowtail   Battus philenor

Pipevine Swallowtail

Battus philenor

Common Checkered Skipper   Pyrgus communis

Common Checkered Skipper

Pyrgus communis

Cabbage Butterfly   Pieris rapae

Cabbage Butterfly

Pieris rapae

Propertius Dusky-Wing   Erynnis propertius

Propertius Dusky-Wing

Erynnis propertius

Tiger Swallowtail   Papilio rutulus

Tiger Swallowtail

Papilio rutulus



Explore Arthur Shapiro's butterfly transect sites below