Pollination is the lifeblood for any flowering plant, also known as an angiosperm. The plant must come up with a way to be pollinated to reproduce and may seek to attract those in the animal kingdom to help. Birds and insects are the primary target of this symbiotic relationship. To attract pollinators, the plant must offer something attractive, which may differ, depending on how many or what type of animals need to be attracted.
The main thing plants offer bees and some sorts of birds is a free meal, in the form of pollen or nectar. The meal is not exactly free, as the animal, wittingly or not, moves pollen from one flower to the other. This creates an opportunity for cross-pollination. Although some plants are also capable of self-pollination, those who can do this are often capable of cross-pollination as well. Animals in the wild learn very quickly which plants provide them with the sustenance they need and naturally go to those plants.
Often, before even being aware of the plant visually, the sense of smell may provide a key as to which plants need a pollinator. Many flowers produce a sweet scent. Although humans enjoy that scent for the aesthetics, birds and bees prefer the scent because it shows them where the nutrition is. Therefore, the scent of a flower is actually essential to many flowering plants.
If nutrition, scent or colors are not used, the very shape of the flower may serve as an attractant. Some plants, such as certain varieties of orchids, have evolved over the eons to take on certain shapes of other insects. For example, a flower petal may be shaped in such a way as to imitate a female insect. Male insects will attempt to mate with the flower petal, inadvertently picking up pollen and spreading it on. This is known as commensalism, where the relationship is beneficial to only one of the species but not harmful to the other one.
Further, some flowers are shaped in such a way to make them attractive and more accessible to certain species for feeding. Some flowers, such as azaleas, are shaped particularly for hummingbird beaks.
Color is perhaps one of the most overlooked strategies flowers can have. The colors are used in a number of different ways to attract pollinators. Some have lines, indicating the path to the nectar. Some are certain colors, such as blue, which helps those animals that have better seeing light at the ultraviolet end of the spectrum.
In the end, the way flower petals attract insects is the result of years of trial and error by the plants. Those who have the proper genetics continue to reproduce, and, over a long and slow process, improve those strategies. Those plants that cannot adapt quickly enough to attract suitable pollinators eventually die out. Through this process of natural selection, a concept made popular by the English biologist Charles Darwin, the survival of the species continues.