What looks like an hourglass-shaped paint splotch on the thorax of some bees is actually pollen. In the past I often saw these stripes—usually in yellow—and wondered what they were. The bees look like they squeezed through someone’s freshly painted woodenware.
But according to Roxanna Mattingly in her fascinating book, Honey-Maker, the design occurs when pollen-covered bees groom. The honey bee uses her two midlegs to clean pollen from her forelegs and the back of her thorax. However, there’s a place she can’t quite reach, right down the middle of her back.
She swipes each side of her thorax and the pollen in removed in an arc, much like the sweep of a wiper blade on a car. The hourglass design remains after she’s reached as far as she can on each side.