Wild Ginger Reproduction
The flowers of Wild Ginger (Asarum canadense) often escape detection from humans, as they are borne at ground level, beneath the plant’s paired leaves. For years it was assumed that the dark maroon (flesh-like) color of the flower and its accessibility to insects promoted pollination by carrion-seeking flies. It turns out, however, that most fly-pollinated flowers have a rather putrid aroma, which Wild Ginger lacks, so it may not be the lure of decomposing flesh that attracts flies. They have been observed visiting the flowers, collecting pollen and escaping the cold winds of April and early May inside the flowers, but they have not been confirmed as actually pollinating the flowers.
Wild Ginger has two back-up strategies if cross-pollination by insects doesn’t occur. One is self-pollination, when the flower’s pollen-bearing stamens mature and move into a position adjacent to the stigma of the flower (see white anthers pressing against central pistil in photo). The other, and most common, reproductive strategy is through vegetative reproduction – spreading rhizomes just beneath the leaf litter.
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Bloodroot Fruit and Seed Formation
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The process of a Bloodroot (Sanguinaria canadensis) flower becoming a capsule containing seeds is primarily dependent upon insects (usually small, solitary, native bees) pollinating the flower. Two to three hours after the flower has opened, some of the stamens begin to release their pollen. Bees (often dark and hairy so that they may absorb warmth from the sun and fly in cool temperatures) transport pollen to a female stigma, thereby pollinating the flower. Within 12 hours of pollination the flower’s stamens wither and the petals fall soon thereafter (see photo). If by the third day after opening the flower has not been cross-pollinated by insects, some of the stamens bend inward toward the stigma, enabling the plant to self-pollinate. (Spring Wildflowers of the Northeast by Carol Gracie)
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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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Hummingbird Clearwing Moths Pollinating Flowers
The Hummingbird Clearwing Moth (Hemaris thysbe) is a familiar sight to anyone with a garden full of beebalm, phlox, verbena or butterfly bush. Clearly named after its similar appearance and hovering behavior to hummingbirds (as well as its partially transparent wings where scales have fallen off) this day-flying moth is an excellent pollinator.
Because its tongue, or proboscis, is so long, the Hummingbird Clearwing Moth can reach nectar located at the base of tubular-shaped flowers. If you look closely at this photograph, you’ll see a tiny clump of pollen near the base of the moth’s proboscis. The structure of the Beebalm (Monarda sp.) it’s visiting is such that the stigmas (tips of the pollen-bearing male structures, or stamens) projecting from the upper lip of the flower are located where the moth will come in contact with them as it inserts its proboscis down into the flower’s nectaries. Hummingbird Clearwings carry their proboscis rolled up under their head and unfurl it when approaching a flower. (Thanks to Sally Fellows and Terry Marron for photo opportunity.)
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Witch Hazel Pollinators
October through mid-November is the typical flowering time for Witch Hazel. The last of the blossoms of this fall-blooming shrub can still be seen in parts of the Northeast. Its long, bright-yellow petals and the presence of a sweet-smelling nectar tell you that Witch Hazel flowers are pollinated by insects. However, there are very few insects present this late in the year and its pollinators have been elusive to the human eye. With the exception of syrphid, or hover, flies, I have never seen any insects visiting these flowers.
It turns out that I was observing them at the wrong time of day. Naturalist Bernd Heinrich discovered that a group of owlet moths called winter moths are active on cold nights and regularly visit Witch Hazel. These moths have the ability to heat themselves by using energy to shiver, raising their body temperatures by as much as 50 degrees in order to fly in search of food. Solved is the mystery of what pollinating insects are still active this late in the year!
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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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Crab Spiders Active
Trailing Arbutus (Epigaea repens) is one of our earliest spring wildflowers. Sometime in April or May the creeping, leathery, evergreen leaves of this plant suddenly come alive with white or pink tubular flowers. While they are delightful to look at, their fragrance is what truly sets them apart from many other plants that flower this time of year.
Because there aren’t that many insects about this early, nor flowering plants, insect predators can have a challenging time finding prey. The pictured crab spider chose its perch wisely: bumble bees are the main pollinators of Trailing Arbutus, and queens are out scouting for food as they begin to establish their colonies.
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Bottle Gentian Pollination
Getting inside the flower of Bottle Gentian or Closed Gentian (Gentiana clausa), one of our latest flowering plants, in order to collect nectar and pollen is a monumental task that few insects, other than fairly large species of bumble bees, attempt. The petals are closed so tightly it takes even bumblebees several seconds of pushing, shoving and cramming to push the petals aside and get through the miniscule opening at the top of the blossom.
Pollen is the primary bumblebee attractant, as the sugar concentration of Bottle Gentian’s nectar is fairly low. Some bumble bees take a short cut – they chew a hole to gain access to the reproductive parts of the flower. The hole is often two-thirds of the way up the blossom, directly opposite the pollen-laden anthers within the flower. Look closely at the hole in the lefthand blossom in the photograph and the adjacent, dissected blossom, and you will see that the bee’s aim was dead on. You can even detect a portion of the anther through the hole.
Flight of the Bumblebee
If you examine plants that are still flowering this late in the season (such as asters, goldenrod and late-blooming turtlehead) early in the morning when it’s still quite cool or late in the day, many of the pollinators you see will be bumblebees, not honey bees. One reason for this is that they have different temperature tolerances for flight. You rarely see a honey bee when the temperature is below 57°F as they cannot fly when it is this cool. Bumblebees, however, are capable of flight when the air temperature is as low as 50°F.
Even so, bumblebees cannot take off unless their flight muscles are above 86°F; they maintain the temperature of their thorax (where wings and wing muscles are located) between 86°F and 104°F regardless of the ambient temperature. The way in which they raise the temperature of their thorax involves uncoupling their wing muscles so that the wings themselves do not move. They then use their wing muscles to shiver and raise the temperature of their thorax until it’s sufficiently warm enough for them to fly.
At rest a bumblebee’s body temperature will fall to that of its surroundings. If it is cool out, and the bumblebee wants to take flight, you can actually see its abdomen pumping to ventilate the flight muscles. An entomologist studying this phenomenon discovered that the rate of pumping can give an indication of the temperature of the bee. It ranges from around 1 pump per second when the bee is 86°F, to 6 pumps per second when it reaches 95°F.
Boneset & Honey Bees
Pollinators of the plant known as Boneset (Eupatorium perfoliatum) are too many to list. The nectar and pollen of its fragrant flowers which bloom in late summer and fall attract many kinds of insects, including bees, flies, wasps, butterflies, and beetles. Being a member of the Composite family, Boneset’s flower structure is such that the nectar is very accessible and therefore a popular feeding site, especially for Honey Bees (see photo) which are reliant this time of year upon the flat-topped clusters of small, white flowers for nectar which they convert to honey and store for their winter supply of food.
Pruinose Squash Bees
The Pruinose Squash Bee (Peponapis pruinosa) is most often noticed when it’s gathering nectar or pollen from squash, pumpkin, watermelon or gourd blossoms. (Squash bees have been shown to be excellent pollinators of zucchini and butternut squashes, among others. If numerous, they thoroughly pollinate all available flowers, rendering later visits of honeybees superfluous. Before Europeans brought honeybees to the New World, squash bees were busy aiding the adoption, domestication, spread, and production of squashes and gourds by indigenous peoples throughout the Americas.) The bee’s black and white striped abdomen is easy to recognize.
While female squash bees are busy foraging for pollen in the flowers of plants in the Cucurbitae family, male squash bees can be seen darting between flowers, searching for mates. By noon, they are fast asleep in the withered flowers.
Pruinose Squash Bees are solitary bees, with every female digging her own nest in the ground. These consist of vertical tunnels that end with a number of individual chambers that are a foot or two deep in the soil. Each chamber is provided with an egg and a lump of pollen so that when the egg hatches, food is readily available. (Photo: five Pruinose Squash Bees packed into a single Bindweed flower)
Carpenter Bees Hibernating
If your home, shed or barn has weathered, unpainted wood and is riddled with ½”-diameter, perfectly round holes, there is a chance that carpenter bees are hibernating in them. Carpenter bees resemble bumblebees in both size and appearance (a carpenter bee has very few hairs on the top of its abdomen, which appears black and shiny, whereas bumble bee abdomens are often yellow and hairy), but they are not social insects. Instead of having a common nest in which they live and raise their young, carpenter bees drill holes in wooden structures or trees inside of which they chew tunnels that contain six to eight brood chambers for their young. After creating the chambers, the female carpenter bee places a portion of “bee bread” (a mixture of pollen and regurgitated nectar) in each one. On top of each pile of food she lays an egg and then seals off the chamber. The larvae eat and grow, pupate and emerge as adult bees in late summer. At this point they feed on nectar, pollinating a wide variety of flowers before they return to their tunnels to over-winter.
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Broad-leaved Helleborine Dispersing Pollen
Having known since childhood that most insects have only one pair of antennae, imagine my surprise when I came upon a hornet on Queen Anne’s Lace that appeared to have two: a pair of slender, black antennae, and between them, a shorter pair of white ones. A bit of research revealed to me that in fact, these white “antennae” were actually the pollen sacs (pollinia) of an introduced and somewhat invasive orchid, Broad-leaved Helleborine (Epipactis helleborine).
Broad-leaved Helleborine is entirely dependent on insects to spread its pollen, especially wasps. It attracts them with nectar, which is said to have an alcoholic and narcotic effect which may help with the spreading of pollen, as an inebriated wasp is less likely to clean pollen off its body before leaving. Helleborine also produces a chemical which other plants produce and use to signal that they are being attacked by insects. It is used purely as a ruse by Helleborine, in order to attract wasps, Helleborine’s primary pollinators, who arrive to fend off other insects, and end up inadvertently collecting Helleborine’s pollinia.
Unlike the pollen of most plants, Helleborine’s pollen grains are so sticky that they cannot separate – thus, the entire package of pollen remains intact and is removed at one time. Wasps are capable of reaching the plant’s nectar without disturbing the pollinia, but cannot crawl out of the flower without striking against and detaching them and in so doing, getting them stuck to their heads. Can you find the pollinia in the insert photograph of a Broad-leaved Helleborine flower (which has not been visited by a wasp yet)?
Due to computer issues, Naturally Curious will resume posts next Tuesday, August 16.
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Butterflies As Pollinators
Butterflies pollinate during the day while most flowers are open and they have better color perception than bees or even humans, but they are less efficient than bees at moving pollen between plants. Their legs and proboscis are longer and farther away from the flower’s pollen so they do not pick up as much pollen on their bodies. They also lack specialized structures for collecting pollen. Nevertheless, it is hard to imagine that some of the Daylily pollen that has collected on this Eastern Tiger Swallowtail’s wings might not fall onto or be brushed against the stigma of the next Daylily it visits.
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Miterwort Flowering
Miterwort (Mitella diphylla), also called Bishop’s Cap, is named for the resemblance of its two-peaked fruits to the hats (known as miters) worn by bishops of the Roman Catholic Church. This spring wildflower produces miniature five-pointed snowflake flowers that beg to be examined with a hand lens.
Gnats, small bees and syrphid flies all seek out Miterwort for its nectar. Because its nectaries are located just below the stamens, the flower is pollinated by the mouthparts of the pollinators which brush against the stamens when collecting nectar and the inadvertently-gathered pollen is transported to other Miterworts. Predators such as the Goldenrod Crab Spider (pictured) know that potential meals are plentiful near these delicate flowers.
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Bumblebees Foraging Fall Flowers
With frost just a whisper away, and in some areas not even that, there are still hardy plants, many in the Composite family (goldenrods, asters, thistles, Queen Anne’s Lace, Yarrow), which defy the odds and optimistically send forth blossoms on the off chance that there are still pollinators on the wing. Fortunately for them, bumblebees can and do fly at much cooler temperatures than honeybees and other pollinators. When food is plentiful and outside temperatures fall below 50°F., bumblebees generally stay inside their nest and live off their stores. At times when food is scarce or stores are low, they will forage when the outside temperature is as low as 43°F. (In severe conditions they have even been known to vary their flying height to and from the nest to take advantage of any temperature differences.) Locally, Tri-colored Bumblebees (Bombus ternarius) have a near monopoly on the last vestiges of nectar and pollen (see photo).
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Turtlehead Flowering & Being Pollinated By Bumblebees
Turtlehead, Chelone glabra, a member of the Plantain family (Plantaginaceae), can be found growing along stream banks and wetlands throughout eastern North America. Its long arching upper lip, or hood, overlaps the lower lip like a turtle’s beak, giving Turtlehead its common name. The male parts of the flower mature before the female parts, and when pollen is being produced these lips are very hard to pry open. Pollinators are primarily bumblebees, which are some of the only insects that have the strength to open the flower. When the female pistil matures, the lips relax a bit, so entry is easier, but access to the nectar at the base of the flower is restricted (by a sterile stamen) to long-tongued insects. Thus, it is specifically long-tongued bumblebees that are able to both enter the flower and to reach the nectar. If you look on the sides of the flowers, occasionally you will find where impatient bumblebees have chewed through to the nectar, avoiding the struggles involved in entering the flower in the traditional manner.
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Goldenrod Crucial To Honeybee Survival
Goldenrod is one of the most important flowering plants for honeybees because it is a prolific producer of nectar and pollen late in the year. Blooming in the late summer and fall, this bright yellow-flowered composite provides nectar for the bees to build up stores of honey for winter. (Goldenrod honey is dark amber and strong tasting.) Goldenrod also provides pollen to help stimulate the colony to produce brood late into the fall. The pollen adds considerable amounts of protein, fats, and minerals to the diet of the late-season bees, helping ensure that they will have food throughout the winter.
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Ragged Robin Flowering
Ragged Robin, Lychnis flos-cuculi, is native to Europe and has become so abundant in northern United States that it borders on being considered an invasive plant. Found usually in wet areas such as marshes, fens and wet meadows, this perennial can cover an area as large as an acre. When flowering, Ragged Robin is very noticeable — not only to humans, but also to the many insects that pollinate it. Bees and butterflies, especially, flock to stands of this plant in order to obtain its nectar and white pollen. (If you suck the base of the flower, you will soon detect the sweetness that attracts pollinators.)
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