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U.S. Forest Service

Visual Cues

Many flowers use visual cues to attract pollinators: showy petals and sepals, nectar guides, shape, size, and color.

  • trout lily
    Members of the lily family such as the trout lily have very showy sepals and petals that are indistinguishable and are technically called tepals. Photo by Charles Peirce.
  • Iris missouriensis
    Nectar Guides
    The nectar guides on the Iris missouriensis readily direct a bumblebee down between the sepal and the style arm. Photo by Al Schneider.
  • azalea
    The flower of the native azalea is uniquely shaped for a ruby-throated hummingbird to sample the nectar and contact the exserted stamens and stigma. Photo by Larry Stritch.
  • American lotus
    The large (to 13-inches diameter) flowers of American lotus are easily seen from afar and provide a broad landing area for beetles. Photo by Larry Stritch.
  • bird's-foot violet
    The blue petals of the bird's-foot violet attracts bees who view these flowers in the ultraviolet range. Photo by Larry Stritch.

Plants that use visual cues have showy sepals or petals with obvious coloration and color patterns. Plants with red or yellow flowers tend to attract butterflies and hummingbirds. Some flowers feature nectar guides that are specific to particular pollinators.

Escape Act

Some flowers have evolved shapes that would seem to defy being pollinated; such is the case with the bottle gentian (Gentiana andrewsii). In this species of wildflower, a bumblebee comes to the top of the flower and forcibly spreads the corolla open and enters the flower completely. The bumblebee then turns around and exits the flower in the same way.

Bumblebee entering the bottle gentian flower. The bee enters the flower.

Bumblebee exiting the bottle gentian flower. The bee leaves the bottle gentian flower. Photos by Charles Peirce.

Nectar guides are patterns seen in some flowers that guide pollinators to the nectar and pollen. In many bee-pollinated flowers, there is a region of low ultraviolet reflectance near the center of each petal. The ultraviolet patterns are invisible to humans, as our vision does not detect ultraviolet light, but bees can detect ultraviolet light. This contrasting ultraviolet pattern helps the bee locate the flower's center.

An olive butterfly on olive early goldenrod. Olive early goldenrod. An olive butterfly on goldenrod in late summer. Photo by Tom Barnes.

A white moth on a white mayflower. This pollinating moth blends in with its background during the day. Moths easily see white flowers after sunset. Photo by Charles Peirce.

A black-chinned hummingbird pollinating yellow columbine. A black-chinned hummingbird pollinating yellow columbine. Photo by Beth K. Hawkins.

Flower shape and size provides visual clues and a structure that allows a specific, co-evolved pollinator to contact the flower's anthers and stigmas. Beetle pollinated flowers tend to have larger and more open flowers that provide an easy landing pad since beetles are not as agile in flight as other flying insects. Non-hovering pollinators require landing pads on the flower so they can rest or feed and contact the flower's pollen. The long nectar spurs of plants in the mint family protects the nectar from being stolen by robber insects and allows the nectar to be accessed by the specific pollinators such as hawkmoths, butterflies and hummingbirds that access the nectar with a long proboscis or a long narrow bill.

Beetle on a primrose. Beetles can land on the large petals of flowers and pollinate the flower while eating pollen and other floral parts. Photo by Larry Stritch.

Bee on a purple coneflower. This purple coneflower provides an easy landing pad for a bumblebee to land on and collect pollen. Photo by Teresa Prendusi.

A ruby-throated hummingbird samples a scarlet beebalm flower. This scarlet beebalm's long nectar spur is easily sampled by a ruby-throated hummingbird. Photo by Joseph Schneid.

A clear wing hawkmoth hovers and samples nectar from this Liatris spicata. A clear wing hawkmoth hovers and samples nectar from this Liatris and in the process rubs its body up against the flower's anthers and pistil. Photo by Tom Barnes.

A butterfly on a Turk's cap lily. Turk's cap lily with its pendant flowers is uniquely shaped to be accessed and pollinated by butterflies. Photo by Tom Barnes.

Bats and moths that are active at night may locate flowers that are white or a very pale color visually. These nocturnal flowers heavy with fragrance and copious, dilute nectar, attract these pollinators.

Irises produce numerous very large flowers in a colorful spike inflorescence. The flowers are large and numerous to compete with the surrounding flowering plants that are competing for the pollination services of bumblebees. Irises have the energy to invest in these floral displays because of the large rhizomes that can store energy and their leaves can absorb sun light from both surfaces instead of the usual upper surface characteristic of most flowering plants and are aligned in such a manner as to capture direct sunlight throughout the day.

For a comparison of different flowering types and the pollinators that are attracted to them visit our Pollinator Syndromes web page.

Field of copper irises. Bumblebees easily spot a beautiful wetland of colorful copper iris in full bloom from very long distances.