BOULDER (AP) – It’s the time of year that honeybee swarms typically start to take wing, setting beekeepers’ phone lines ablaze as word spreads about their availability to collect and place in awaiting hives.

But anxiety is running high in the local beekeeping community as April draws to a close, with word-of-mouth reporting of a high number of lost colonies over the winter. Firm explanations are proving elusive.

Hygiene-area beekeeper Tony Lewis lost eight out of his 10 colonies over the winter – and can’t figure out why.

“It’s the highest loss I’ve ever had. I’ve come close to that (before), but not quite,” Lewis said.

As for possible reasons, he said, “This is totally anecdotal ... but it seems like people in Boulder Valley lost more than in Denver, but who ... knows why? It is so speculative. Is there more pesticide use and herbicide use (in Boulder County) because it is more ag than Denver? Maybe.”

Lafayette resident Bill Pomeroy had two active hives going into the winter, and now has just one. He has heard about high losses suffered locally, including another Lafayette beekeeper who lost a dozen colonies.

“It’s crazy,” Pomeroy said.

One theory he’d heard is the suggestion that nanoparticles of aluminum in so-called “chemtrails” left by airplanes are working their way into the environment at a level that is having a negative effect on pollinators.

This idea has been branded by many to be little more than a conspiracy theory. A group of scientists from the University of California-Irvine surveyed 77 atmospheric chemists and geoscientists and 76 said they had found no evidence of such spraying, according to an article on seeker.com.

The Front Range experienced an unusually mild autumn and a relatively mild winter, but Pomeroy doesn’t see that as a factor.

“If anything, they would have been able to survive better, because they wouldn’t be eating so much” of the honey that they store and depend on to survive the winter season, he said.

But Lewis floated a possible explanation related to climate change.

That theory, he said, is that, “Because we have these really warm days in the winter that we never used to have ... they come out of their balls that they bunch up in, in the hive, to keep warm.

“Then, when it gets cold again quickly, they don’t get back into their ball. But who the hell knows?”

Beth Conrey, a Berthoud resident and past president of the Colorado State Beekeepers Association, as well as current vice president of Boulder County Beekeepers Association, said in an email, “I have heard rumors of large losses but can neither confirm nor deny them as I have no locally collected data from which to draw.

“Personally,” she added, “I sustained 20 percent losses. This is much better than previous years but still unsustainable. Imagine if it were cattle or corn ... I had a neighbor who lost all eight of his hives. His daughter lost all three of hers. I am certain there are folks around the state with similar tales to tell.”

The losses are far more than rumor, according to man whose livelihood is bees – Tim Brod, owner and operator of Highland Honey, based in unincorporated Boulder County, who currently presides over 165 to 180 hives in multiple locations. He believes that he might have seen 35 to 40 percent of his hives go dark over the winter. But he has heard figures tossed around by others of losses as high as 60 percent.

“It’s just, like, so depressing,” Brod said.

He is convinced there is no simple explanation for the current situation.

“When you’re looking at a biological system, there’s not one single factor,” he said. “There’s a constellation of events going on, and those events get more intensified when you live in a highly populated area.”

Brod sees three factors at work. One is the increased use of pesticides and herbicides. Another is the decrease in available forage for apian life as development continues across the Front Range. The third leg of the stool is backyard beekeepers doing an inadequate job of learning about – and treating their bees for – Varroa destructor, a parasitic mite that attacks honeybees in their hives.

“There’s not enough people who thoroughly understand Varroa and are treating for it,” Brod said. “The last thing I want to do – we don’t want to blame backyard beekeepers, because backyard beekeepers are responsible for kicking the wheel of awareness for helping us change laws and regulations” regulating the use of harmful chemicals. But, he said, “There is more backyard beekeepers need to do.”

Tom Theobald of Niwot is also a past president of the state beekeepers’ association and a founder of the Boulder County Beekeepers Association. He has heard of hive losses locally this winter of up to 80 percent.

On the list of culprits, Theobald rates high the use of neonicotinoids, a class of neuroactive insecticides. The estimated 4 million pounds that are used each year nationally on crops, he said, represent only about 10 percent of the total neonicotinoid use, with the other 90 percent going to seed treatment. With an estimated 5,000 to 10,000 times more toxicity than DDT, Theobald said, neonicotinoids are having a devastating effect on pollinators.

Once the keeper of about 200 hives, Theobald said last year he was down to 12 – and that none of those survived this winter.

“Every year is unprecedented,” Theobald said. “This is my 42nd year of beekeeping. Before these problems began, my losses would have been on the order of 2 to 5 percent. In a really severe winter or unusual circumstances, that might have gone to 10 percent. But what we’re seeing now is unprecedented. And it’s getting worse every year.”

Brod urged support for HJR 17-1029, the Colorado Highway Pollinator bill, a resolution to designate U.S. 76 from Denver to the Nebraska state line as a bee-friendly highway. It would encourage the Colorado Department of Transportation to manage the right-of-way to promote pollinator habitat. Rep. KC Becker, D-Boulder, is a primary sponsor.

With significant winter hive loss and beekeepers typically dependent on swarm hotlines to replenish or stock their backyard hives, there’s a possibility there simply won’t be enough swarms to go around this spring, Conrey said.

“Insufficient swarms have happened before,” she said. “We have had several years when swarm seasons were poor. And when that happens, people simply have to do without. Can’t create them.”