Where Have All the Monarch Butterflies Gone?

(March 20) -- For the beloved monarch butterfly, these are dire times.

In the 1980s, as many as 170,000 monarchs would descend each fall and spring upon Natural Bridges State Beach in Santa Cruz, Calif., to spend the winter in a seaside eucalyptus grove.

This year, however, just 3,800 monarchs showed up, a new low in what has been a steady and precipitous drop-off in population. And the problem is not localized to California.

"Across the country, we're looking at the lowest returning monarch population we've ever seen," said Chip Taylor, professor of entomology at the University of Kansas and the director of Monarch Watch, a group that tracks the butterflies. "It's a bit curious as to the reason we're seeing such precipitous declines, but we do have theories."

Though virtually indistinguishable, America's monarch butterflies are divided into two groups, those located to the east of the Rocky Mountains and those to the west. The eastern butterflies undertake one of the longest annual migrations in the insect world, with some flying upward of 3,000 miles between Canada and Mexico. Western butterflies winter along the coast of California but have a range that extends to several states and southern Canada.

Taylor told AOL News that a combination of factors is likely responsible for the swift decline in the number of monarchs gracing American skies.

First, Taylor said, is the degradation of the eastern monarch's wintering grounds around Michoacan, Mexico, because of continued deforestation of areas where the butterflies typically congregate.

Second is the loss of habitat in the United States. Monarch caterpillars exclusively feed on milkweed, which grows wild in much of the country but is often removed or killed off with pesticides when wild lands are adapted for other uses.

Third is climate change. "California and much of the West has gotten warmer in recent years," Taylor said, "drying up sources of water that the butterflies rely upon. In the East, we've had a few colder-than-usual summers. I tell people we have a Goldilocks situation with the butterflies. They don't like it too warm and they don't like it too cold."

Another card in the deck that seems to be stacked against the monarch is that the percentage of females of the species has dropped over the past few decades. Andy Davis, a researcher at the University of Georgia, conducted a study in which he discovered that while 54 percent of all monarchs were female in the middle 1970s, only 43 percent are today.

While a single female butterfly can lay as many as 400 eggs, Davis agrees that the swift decline in the monarch's numbers is a result of trends that will make it difficult for the insects to make a comeback anytime soon.

"My finding was just one more nail in the coffin," Davis told AOL News. "In tandem with the overall population crash, the fact that there are fewer females means that it's that much harder for the monarchs to rebound."

Disappearing Milkweed

The plant vital for the survival of the monarch is milkweed. Adult females lay their eggs upon its stems and leaves, and when the caterpillars hatch, they feast on milkweed leaves alone.

A flowering weed that grows naturally from coast to coast, milkweed has fast been disappearing from the American landscape.

"Every year teachers go out and collect milkweed with monarch eggs and keep it in the classroom to track the life cycle of this magnificent creature, " said Martha Nitzberg, an interpretive naturalist at Natural Bridges State Beach. "But lately we've heard from teachers who say they can't find any milkweed. It's just not there."

Nitzberg said a big reason is that California began using herbicide to control weeds along roadways and on railroad tracks.

The milkweed problem is just as true east of the Rockies, with land where the plant has typically grown being gobbled up by development. "We've lost 147 million acres of habitat," said Taylor. "To put it into perspective, that's three times the size of the state of Illinois."

In hopes of re-establishing the crucial food source for the caterpillar, Monarch Watch has launched a campaign to encourage individuals, businesses and parks to plant indigenous milkweed.

"We hope that people will start to take an interest in these pollinators," Taylor said. "If they don't, we may get to the point where the migration of the monarchs will be in such small numbers that people won't even notice them."

While the ultimate prognosis for the monarch remains uncertain, Taylor, Nitzberg and Davis all concur that the loss of one of the continent's most iconic insects would be a tragedy.

"A couple of years ago I would have said it was unlikely that we'd lose it [the monarch]," Davis said. "But this year paints a dire picture."