Japanese Knotweed (Fallopia japonica) was introduced from Japan in the 1800’s as an ornamental; it was widely cultivated, escaped and is now well established throughout the Northeast. The World Conservation Union lists Japanese Knotweed among the top 100 worst invasive plants. Its dense canopy and rapid spread through underground rhizomes make it a formidable threat to native plants and the animals that depend on them.
There are some redeeming qualities to this invasive plant, however. In addition to goldenrod and asters, Japanese Knotweed is a crucial source of late-season nectar and pollen. At this time of year, when Japanese Knotweed flowers, you can almost locate a stand using just your ears, the buzzing of honey bees gathering the last of their winter food supply from the thousands of tiny flowers is so loud. A wide variety of insects can be found on this member of the Buckwheat family eating leaves, foraging for nectar and pollen, and preying on the former. A recent survey revealed honey bees, bumble bees, ladybug beetles, flies, hornets, yellow jackets, stink bugs and tussock caterpillars, to name just a few.
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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)
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.
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.
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).
Grass of Parnassus, Parnassia glauca, (also known as Bog- Star) was named after Mount Parnassus in central Greece. It is not a type of grass, but rather, belongs to the family Celastraceae and can be found growing in fens, bogs and swamps. The striking green lines on its petals guide flies, bees and other pollinating insects to the flower’s supply of nectar.
The structure of Grass of Parnassus’s flower is not typical. In between its five functioning stamens and five petals there is a whorl of five sterile stamens, each of which is three-pronged. The spherical tip of each prong mimics a glistening droplet of nectar. These stamens do not actually produce any nectar – they are there purely to attract pollinators. The actual nectar is located near the base of these false, or sterile, stamens. Only one of the five true stamens in the flower is active at any one time, with each producing pollen on average once every 24 hours.
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.