Monarchs close-up 2016

A pair of Western monarch butterflies warm their wings in the sunshine at Pismo Beach Butterfly Grove in this photo from 2016. The number of migrating butterflies returning to the grove each winter has plummeted over the past 10 years.

The Pismo Beach Butterfly Grove could be left with no butterflies for people to marvel at if, as scientists fear, the use of poisons, the loss of habitat and climate change lead to the extinction of the migrating Western monarchs.

For uncounted centuries, the orange-and-black monarch butterflies have made an aerial voyage down the coast from the Pacific Northwest to California to spend the winter, then journeyed back as spring approached.

Their numbers turned the hanging eucalyptus tree branches from green to orange in the Pismo Beach grove, where they drew thousands of tourists and were celebrated by the State Parks Department’s Western Monarch Butterfly Day.

Volunteer docents who educate the public at the grove on Highway 1 between Grover Beach and Pismo Beach say they’ve never seen the butterflies’ numbers as low as they have this year.

“It’s too depressing to even think about,” said Jan Ojerholm, a resident of Grover Beach and a Central Coast State Parks Association member who has volunteered at the grove for about 10 years.

“In 1990, we had a high count of 230,000 butterflies in the grove,” Ojerholm said. “This year in the Thanksgiving Day count, we had 188, although one person came up with 300, but that wasn’t the official number.

Clustering monarchs 2016

Western monarch butterflies cluster on branches of a tree in the Pismo Beach Butterfly Grove in this photo from 2016 when the wintering insects still numbered in the thousands. The number shown on these two branches could be more than the entire number counted in the grove last November.

“So I’ll let you do the math — from 230,000 to approximately 250,” she said. “It’s sad, it’s really sad.”

The Xerces Society for Invertebrate Conservation, which has conducted the Thanksgiving Day monarch butterfly counts for decades, this year found the state’s Western monarch population at its lowest level ever.

Ojerholm said in the previous two seasons, the number of monarch butterflies overwintering in the entire state of California was about 30,000, which some scientists said is a “quasi-extinction level.”

On Tuesday, the Xerces Society announced the total count for the entire state this winter was 1,914 butterflies.

Driving the drop

The plummeting butterfly population is blamed on three primary causes, according to Ojerholm and the Xerces Society. Those are the use of herbicides and insecticides; habitat lost to urban expansion; and climate change upsetting their life cycle.

It’s easy to figure out how insecticides can kill butterflies and how herbicides and urban growth destroy the milkweed the monarchs lay their eggs on and that provides the only food their larvae eat.

The effects of climate change are not as obvious.

One of the three things monarchs seek out for an overwintering site is a cool climate, Ojerholm explained. The other two are humidity and a grove with a canopy to protect them from the elements.

The butterflies repeatedly mate and reproduce on their summer migration to the Central Coast. In fact, the insects that arrive here are four or five generations removed from the ones that began the journey. But once they get here, the cool winter weather keeps them from reproducing.

“In wintertime, we used to be about 65 degrees here,” Ojerholm said. “It would stay pretty cool. Now each month of the year, we have days in the 70s and even into the 80s.”

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Colorful monarchs 2015

Western monarch butterflies spread their distinctive orange and black wings, highlighted with spots of white, on a eucalyptus branch in the Pismo Beach Butterfly Grove in this 2015 photo.

Those warmer temperatures cause the butterflies to reproduce and begin the journey northward earlier than they should.

“They feel that it’s springtime, time to get a date,” Ojerholm said. “They might be successful [finding milkweed and nectar] locally, but up north it’s cold, things aren’t blooming.”

But exactly what befalls the butterflies after they leave the wintering grounds in Pismo Beach isn’t clearly understood.

“We just don’t know for sure what’s happening to them when they leave the grove,” Ojerholm said.

Local residents have tried to help by planting milkweed and blooming plants, but in some cases that has hindered the butterflies’ survival because milkweed has been planted as close as just across Highway 1.

“You don’t want milkweed within 5 miles of overwintering sites,” Ojerholm said. “You don’t want them to smell it — which they can do with their antenna — from an overwintering site. If they can smell it, they want to find a date and reproduce.”

Too late to recover?

Comparing Western monarch butterfly population 1980s to 2021

A chart used by Xerces Society for Invertebrate Conservation, which has monitored the Western monarch butterfly population, graphically illustrates their decline. For every 250 of the butterflies that wintered in California in the 1980s, at left, only one exists today.

Ironically, back around 2014 when a lot of people were planting butterfly gardens and butterfly way stations, some groups were asking the federal government to remove the monarch from the list of threatened species.

“Every year, we kept thinking this would be the year the numbers would come back up,” Ojerholm said.

Instead of recovering, however, the population continued to not just fall but to plunge.

So there is no endangered species protection for the monarchs’ habitat because they are not yet on that list, and more than half a dozen species seeking protection are in line ahead of them.

“For the Western monarch, it may be too late,” Ojerholm said.

But she noted people can still help, not just by planting gardens with flowering plants that produce nectar but also by monitoring monarchs — reporting when and where they see them flitting about.

“There are a number of websites where they can report their observations,” she said.