On sunny days, you rarely see evening primrose flowers blossoming. As evening sets in, the petals open up within a minute, blossoming only one night long. The flowers emit a strong peculier odor to attract night insects. If the following day is cloudy they will blossom longer. The petals reflect ultra violet light, except at the foot. Because insects can detect ultra violet light, they see a dark heart surrounded by a light halo and are directed to the nectar. There are three species of evening primrose, which closely resemble one another.