The bright colors and sweet smell of flowers attract animals that help the plant to

Natalia Dudareva, an associate professor in the department of horticulture and landscape architecture at Purdue University, explains.

Flowers of many plant species produce a scent. This scent is typically a complex mixture of low molecular weight compounds emitted by flowers into the atmosphere and its structure, color and odor are critical factors in attracting pollinators. Although flowers can be identical in their color or shape, there are no two floral scents that are exactly the same because of the large diversity of volatile compounds and their relative abundances and interactions. Thus, scent is a signal that directs pollinators to a particular flower whose nectar and/or pollen is the reward. Volatiles emitted from flowers function as both long- and short-distance attractants and play a prominent role in the localization and selection of flowers by insects, especially moth-pollinated flowers, which are detected and visited at night. Species pollinated by bees and flies have sweet scents, whereas those pollinated by beetles have strong musty, spicy, or fruity odors.

To date, little is known about how insects respond to individual components found within floral scents, but it is clear that they are capable of distinguishing among complex scent mixtures. In addition to attracting insects to flowers and guiding them to food resources within the flower, floral volatiles are essential in allowing insects to discriminate among plant species and even among individual flowers of a single species. For example, closely related plant species that rely on different types of insects for pollination produce different odors, reflecting the olfactory sensitivities or preferences of the pollinators. By providing species-specific signals, flower fragrances facilitate an insect's ability to learn particular food sources, thereby increasing its foraging efficiency. At the same time, successful pollen transfer (and thus, sexual reproduction) is ensured, which is beneficial to plants.

Plants tend to have their scent output at maximal levels only when the flowers are ready for pollination and when its potential pollinators are active as well. Plants that maximize their output during the day are primarily pollinated by bees or butterflies, whereas those that release their fragrance mostly at night are pollinated by moth and bats. During flower development, newly opened and young flowers, which are not ready to function as pollen donors, produce fewer odors and are less attractive to pollinators than are older flowers. Once a flower has been sufficiently pollinated, quantitative and/or qualitative changes to the floral bouquets lead to a lower attractiveness of these flowers and help to direct pollinators to unpollinated flowers instead, thereby maximizing the reproductive success of the plant.

Flowers are a beautiful addition to gardens, creating spots of color and producing scents that float on the breeze. Some gardeners choose flowers based on their colors and fragrances, inadvertently attracting other garden visitors when planted en masse. The bright colors and pleasant aromas of these plants are easy for potential pollinators to detect from far afield.

Colors and Scents

1. Flowers are the beacons for animal-pollinated plants. They advertise the availability of nectar and pollen, using both color and smells. Over their evolution, plants have managed to tailor their messages to their ideal pollinators, choosing colors and scents most likely to bring them in for a closer inspection. Most flowers house a big food payoff.

Luring in Specific Pollinators

1. Although scent and color can catch the attention of many pollinator species, specific combinations work to reel in specific pollinators. These animals have learned to associate specific combinations with favored plants. Once they get closer, many insects are able to detect ultraviolet markings indicating the location of hidden food sources. Each common pollinator has a set of specific cues based on their visual and olfactory sensitivity.

Cues for Honeybees

1. Bees appear to be unable to detect many wavelengths in the red color spectrum, so most flowers that are pollinated by bees tend to be yellow or blue. These flowers also carry ultraviolet nectar guide coloration that lures bees inside where their sexual organs are located. Bee-pollinated flowers generally produce a mild, fresh odor.

Cues for Butterflies

1. Butterfly-pollinated flowers are on the opposite end of the spectrum from bee-pollinated flowers. Since these insects see better in the red end of the spectrum, their favorite flowers are often red or orange, but can be nearly any color, with very light fragrance. The nectar of these flowers is often hidden in many small tubes.

Cues for Hummingbirds

1. Hummingbirds are the primary non-insect pollinators of flowering plants, with their own special flower-based cues. Since birds don't respond to olfactory signals, flowers that rely on hummingbird pollination have developed bright red or orange flowers with lots of nectar inside. Sometimes, these flowers hang upside down from the plant, but even those that are more erect are designed to allow the bird to feed in flight, with long, tubular flowers.