They usually have a delicate, sweet scent, and a small, narrow floral tube to fit the tongue-length of that species of bee. For example, snapdragons will only open for a bee of the right weight. They are perching feeders. Butterflies walk around on flower clusters probing the blossoms with their tongues. Each flower has a tube of suitable length for the butterfly s tongue.
Moths are nocturnal, have a good sense of smell, and are hover-feeders.
These flowers are white or pale colors so they are visible at night, and may only be open at night. Birds , especially hummingbirds have good eyes which expecially can see red but poor senses of smell. These flowers are brightly-colored, especially red, but have no smell, and have recurved petals so they are out of the way. Those bats which are pollinating species also have good vision and a long, bristly tongue. These flowers are open at night, and are white or light-colored with a musty odor like the bats in order to attract them.