More than two out of five American honeybee colonies died in the past year, and surprisingly the worst die-off was in the summer, according to a federal survey.

Since April 2014, beekeepers lost 42.1 percent of their colonies, the second highest loss rate in nine years, according to an annual survey conducted by a bee partnership that includes the U.S. Department of Agriculture.

"What we're seeing with this bee problem is just a loud signal that there's some bad things happening with our agro-ecosystems," said study co-author Keith Delaplane at the University of Georgia. "We just happen to notice it with the honeybee because they are so easy to count."

But it's not quite as dire as it sounds. That's because after a colony dies, beekeepers then split their surviving colonies, start new ones, and the numbers go back up again, said Delaplane and study co-author Dennis vanEngelsdorp of the University of Maryland.

Oklahoma, Illinois, Iowa, Delaware, Maryland, Pennsylvania, Maine and Wisconsin all saw more than 60 percent of their hives die since April 2014, according to the survey.