Many yellow flowers contain nectar guides, which are patterns of pigments with ultraviolet absorption. The pigments belong to a group of organic compounds called flavanols. Honeybees and other insects with ultraviolet visual sensitivity are attracted to the center of these flowers, as shown in the following images. Interestingly, red flowers don’t contain these nectar guides as they tend to be pollinated by birds.
Some butterflies have UV markings that can be detected by the UVCorder™. Butterflies can see in the UV, and can distinguish males from females by their UV wing patterns.