Monarch butterflies on upward trajectory
Project finds signs of rebound for vanishing species
Three biologists crouched among the milkweed plants, combing through the thin green leaves as if braiding hair. They were looking for tiny white eggs or chubby, yellow-striped caterpillars: signs of the Western monarch butterfly.
Their work was part of a $1.2 million state-funded project to rescue the Western monarch, which until recently seemed to have almost disappeared from California. A year ago, the conservation organization River Partners planted 30,000 milkweeds and other flowering native species in eight locations to restore habitat, mostly in Central California. The biologists’ goal that day at Dos Rios Ranch Preserve, a restored floodplain on a former dairy ranch in Modesto, was to see if the project is working.
“It’s definitely making a difference,” said Angela Laws, conservation biologist at the Xerces Society for Invertebrate Conservation, a partner in the project. “Monarchs are spotty where they show up. So just because we don’t find any today doesn’t mean
they’re not going to use this habitat.”
Monarchs leave the California coast in late winter, heading to inland areas to breed. When they get to the Central Valley this time of year, they need milkweed to lay their eggs; the plant’s pointy green leaves are also food for the caterpillars. The successive generations of butterflies also need other blooming plants like yarrow that provide nectar to refuel for the next stage of their journey, as they travel farther east in California and to other Western states.
The butterflies’ beautiful orange-and-black markings and epic migrations have endeared them to generations of Californians. They also play an important role as pollinators, and scientists say that protecting them helps other butterflies and bees too. Loss of habitat along with pesticide use have caused the monarch population to decline sharply: While 1.3 million were found in California in 1997, their numbers dropped to fewer than 2,000 in winter 2020-21.
But the latest California count, announced in January, shot up to 250,000, which gave conservationists hope for a rebound, though insect populations can swing wildly from year to year. Laws saw evidence of the larger population earlier this April, when she found 12 caterpillars at another restoration site in Bakersfield.
“We were hoping we might see more monarchs this year, and so to see so many right off the bat was really exciting,” she said.
At Dos Rios, the team was inspecting each stem of milkweed in a specific area that Laws checked last year and will revisit several times this summer. Monarchs, caterpillars and eggs could be around anytime from April to October, but the larval stage is only two weeks, so they can be easy to miss, Laws said.
The project’s goal is also to create habitat for other types of pollinators, so the scientists kept track of those too: a fly, which looks like a bee except it hovers rather than sweeps from flower to flower, and a cabbage white butterfly — one of which swooped past the group with linen-white wings.
Haley Mirts, ecologist and monarchs program lead at River Partners, leaned down to inspect the fading purple petals of a phacelia, a native plant that starts blooming in late January and early February. Nearby, she pointed to gum plants that were just about to blossom and then should keep flowering into September to feed the monarchs.
“One thing that we tried to do when we planted these plots was to include flowers that would bloom year round,” she said. “The monarchs are out and they’re they’re laying their eggs during the summertime, but they’re really moving across the state year round.”
In the end, the team didn’t find any evidence of monarch butterfly activity that April day. But a week later, caterpillars were found at another restoration site in Oroville.
Hillary Sardiñas, monarch conservation manager at the California Department of Fish and Wildlife, said the project is part of a multistate restoration plan for Western monarchs to create tens of thousands of acres of habitat in the Central Valley and adjacent foothills.
“One of the things that’s understudied is just really understanding how well the restoration translates into producing more monarchs,” she said. “Hopefully they can take what they’re learning from our sites and then apply it in other areas.”