Look closely at an aster and you may notice that what appears to be a single flower is actually a core of "disk flowers" (the yellow center) surrounded by a ring of "ray flowers" (the "petals"). This flower form is common to all members of the Asteraceae, including sunflowers, coneflowers, dandelions, and goldenrods. Some species have only disk flowers, while others have only ray flowers. If you're lucky, you might catch a bee-mimic syrphid fly feeding on the flowers. Most birds will not eat stinging bees and wasps, and a number of harmless species have also evolved the yellow-and-black coloration to minimize predation risk.