The Western monarch butterfly population in California declined 86 percent in 2018 compared to the previous year, according to the Xerces Society for Invertebrate Conservation, a nonprofit group that conducts an annual survey of the species in the Western United States. Even more stark for the species is that it has dropped a shocking 97 percent since the 1980s, the agency reports.

The butterflies spend winter in California. Many other North American varieties travel to Mexico for the same season. In California, they spend the season in eucalyptus trees.

The Xerces Society said that less than 30,000 butterflies will find their way to the state this year compared to more than 192,000 in 2017. Two decades ago, that number was markedly higher, with more than 1 million doing so in 1997, and “at least 4.5 million in the 1980s.”

The decline is “potentially catastrophic” told biologist Emma Pelton, who oversees the Xerces Society survey, to The New York Times. “We think this is a huge wake-up call.”

According to scientists, the Western monarch populations are in trouble primarily because of habitat loss and pesticides. Environmental conditions, including heavy rain in the states, were another impactful factor.

“There were late rainy season storms that swept across California in March,” the Xerces Society wrote in a blog post. “There was a severe and extended wildfire season in California and, to a lesser extent, in other areas of the butterfly’s breeding and migratory range. Smoke and bad air quality was widespread in parts of the west at times. California is still recovering from a historic drought.”

Why are the butterflies important, or their lowered numbers significant? There are couple of reasons beyond the mere beauty of the creatures.

First, and most important, they are pollinators. If they don't have enough habitat then “many of our other pollinators and wildlife that share their habitat are in trouble as well,” the Monarch Joint Venture states. “Because they are so well known and their decline is easy to see, monarchs are like the proverbial 'canary in the coal mine' for pollinators.”

Their decline can impact human food systems. Additionally, monarchs and other pollinators are part of a “natural food web and ecosystem,” so providing enough habitat, like milkweed for monarchs, is essential in maintaining a balanced food web within the ecosystems that are critical in sustaining us, the advocate agency said on its website.

Second, monarchs are good for the science and education communities.

According to the Xerces Society, congregations of wintering monarchs have been found at more than 400 sites along the California coast, from Mendocino County in the north to San Diego in the south. Monarchs are generally present from October through February and wintering populations may peak at different times.

For its report, the Xerces Society analyzed results from 97 of its survey sites, accounting for 77 percent of the state’s total wintering population. In 2017, these 97 sites hosted about 148,000 monarchs. In 2018, scientists and volunteers counted just 20,456. The society conducts annual Thanksgiving and New Year’s counts. It said there is no substantial evidence of a delayed migration and butterflies are not being reported in other parts of the country.

A separate 2017 study by Washington State University researchers found the species likely will go extinct in the next few decades if nothing is done to save it.

A four-decade-old University of Florida study found that the number of caterpillars and butterflies in North Florida has been declining since 1985. Since 2005, the numbers have dropped by 80 percent. These specific insects winter in Mexico, but the results suggest that butterfly populations across the continent are sharply dropping.

Monarchs have one of the most complicated migration patterns of any insect known, returning to the same trees each year, a specific behavior unique to the monarch butterfly.

Another finding of the Florida study: Monarchs time their departure from Mexico in the spring so it coincides with the optimal growth of milkweed in Florida and other Southern states. The plants contain toxins that they store up to ward off predators.