You've probably seen a blue moon, which happens every two to three years. That's when a second full moon occurs in a single calendar month.

You've also probably seen blueprints, blue books and blue-plate specials. You've sung the blues and you've been blue.

But, have you ever seen a blue honey bee? As blue as...well...a blueberry?

We recently visited the half-acre Häagen-Dazs Honey Bee Haven on Bee Biology Road, University of California, Davis, when we saw a...drum roll...blue bee! It was foraging on a purple coneflower.

I captured the image with a Nikon D700 camera, equipped with a 105mm macro lens. Settings: shutter speed, 1/160 of a second; 6.3 f-stop; and 800 ISO. No flash. No tripod.

Honey bee guru/Extension apiculturist Eric Mussen of the UC Davis Department of Entomology and Nematology looked at the photo and agreed it was a blue bee. 

Now Mussen, who has been with the department since 1976 and is a favorite of the national news media, knows bees. He's also captured many images of bees, none blue (although many beekeepers have turned blue, especially during massive colony losses).

So, a blue bee?

"The exoskeletons of insects are waxy and oily," Mussen said. "Given just the right angle to the sun, you can see structural colors that are not the true pigments of the exoskeleton. In fact, there are some very shiny, metallic-looking insects that lose their sheen when they die, never to be seen again."

Just the right angle to the sun.

Once in a blue moon...