They call it "colony collapse disorder." Thousands of bees vanish, and nobody knows why.

It's happening all over North America. Honeybees are disappearing. They're not dying, and they're not failing to reproduce. They're just . . . leaving; often half the bees in a colony just fly away and don't come back. Scientists don't know where they're going or why. but half the populations have left apiraries in 24 states. Here's a typical case in San Antonio, Texas.

To see a video version of the disappearing bee story, check NBC's Nightly News, which featured the mystery on Wednesday (scroll down and click the headline "Where have all the bees gone?").

While scientists studying this baffling phenomenon don't know where the bees are going or why, they are more certain about some of the negative impacts their departures will mean. About a third of the food we eat depends on the pollination bees provide. Honey comes to mind immediately, but fruit and vegetables depend on bees for pollination. So does alfalfa, and it's food for cattle, so that means getting stung at the market as scarcity drives prices higher.

Then there are the troubling implications for the ecosystem and for plants in the natural world. There's no replacement for bees; nothing can pollinate nearly as well as they can. One of the foremost authorities on bees and pollination in this country is Dr. Peter Kevan at the University of Guelph. And you can get more information about bees and other pollinators online, too.