Bumblebees Nectar Robbing
Flowering plants have a mutually beneficial arrangement with pollinators. Insects and other pollinators that visit flowers inadvertently pollinate them when they retrieve nectar and pollen – a win-win situation for both flower and pollinator. Occasionally, however, creatures opt for a short cut to a flower’s nectaries and instead of entering the flower through its natural opening, they bite “robbing holes” that lead directly to the nectaries, bypassing the flower’s reproductive structures; consequently they do not pollinate the flower.
Charles Darwin refers to bumble bees “stealing” nectar from flowers in this manner in his 1859 book, The Origin of Species. Nectar robbers include species of carpenter bees, bumble bees, solitary bees, wasps, ants, hummingbirds, and some songbirds. In this photograph a bumble bee is chewing a hole at the base of a Cardinal Flower in order to access the flower’s nectaries more directly.
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Ruby-throated Hummingbirds Pollinating Cardinal Flower
Cardinal Flowers are to Ruby-throated Hummingbirds what Goldenrod is to Honey Bees in the fall — an important source of nutrients just when it’s needed most. Just as hummingbirds are preparing for their migration south and nearly doubling their weight (from about 3.25 grams to 6 grams) before crossing the Gulf of Mexico, Cardinal Flower blossoms. A single migration can mean a nonstop flight of up to 500 miles over a period of 18 to 22 hours and nectar such as they obtain from Cardinal Flower helps sustain them. This relationship is not one-sided however – it is mutually beneficial for both the bird and the plant. In acquiring nectar from the blossoms of Cardinal Flower, hummingbirds inadvertently perform a crucial task, that of pollinating many of the flowers they visit.
The blossoms of Cardinal Flower have two phases. In one the male reproductive part of the flower (the white “moustache” you see above the petals) matures and produces pollen. After the male structure matures and disappears, the female reproductive part develops and extends out from the same place where the male flower was. The flower parts mature at different times in different flowers on a given stalk, so both male and female flowers are present on the same plant at the same time. In order to reach the nectar from Cardinal Flower, a hummingbird must get into a position where the top of its head brushes against the flower’s reproductive parts. If the flower is in the male phase the hummingbird’s head gets dusted with pollen (see inset). If the flower it visits is in the female phase, the pollen on its head (from previous visits to male flowers) is deposited on the stigma of a female flower, pollinating the flower.
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Cardinal Flower Blossoming
You can’t get much redder than the red of Cardinal Flowers. Their petals act as brilliant red flags beckoning Ruby-throated Hummingbirds, who favor red, to come drink their nectar (and at the same time, pollinate them). Because their chief pollinator has wings and the ability to hover as it drinks, Cardinal Flower has no need for a landing platform, which most insect-pollinated flowers have.
Cardinal Flower has both male and female flowers. Above the red petals is a red tube, at the tip of which the reproductive parts of the flower emerge. First to appear are the male flowers, displaying pollen-bearing stamens. After they die, sticky, Y-shaped pistils extend from the flower, ready to receive pollen. The female flowers thus follow the male flowers (protandry). These flowers mature from the bottom to the top of the spike and you often see both male and female flowers on the same plant (just barely discernible in pictured flower spike).
Male flowers produce more nectar than female flowers, and hummingbirds seem to know this, as they spend most of their time at the youngest, and therefore male, flowers on the top half of the flower spike.
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