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.
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.
Large-flowered Trillium (Trillium grandiflorum), also known as White Wake-Robin, is our largest and showiest species of trillium. It can be found throughout New England’s rich woods, sometimes carpeting large expanses of the forest floor in May and June. All species of trillium, as their name implies, have parts arranged in threes, or in multiples of three (petals, bracts, leaves, stamens, carpels).
Nectar, not fragrance, attracts long-tongued bumblebees to Large-flowered Trillium’s funnel-shaped blossoms. Self-pollination occasionally occurs, aided by the fact that as the flowers age, their stigmas reflex downward and come in contact with the anthers. The flowers are exceptionally long-lived, remaining open and fertile for two to three weeks.
When they first open, Large-flowered Trillium’s petals are white. As the flowers age, they become pale to deep pink (see insert). (There is also a pink form of Large-flowered Trillium which is pink from the time of opening.) The seeds that form are dispersed primarily by ants, but yellow jackets, harvestmen and white-tailed deer also contribute to their dispersal. It takes two years for the seeds to germinate and once established, Large-flowered Trillium plants typically require seven to ten years in optimal conditions to reach flowering size.
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.
Flowers that have limited opportunity to attract pollinating insects, such as those that mature very early in the spring, often are self-fertile – they can produce seeds without the benefit of pollinators. Wild Ginger (Asarum canadense) is a perfect example of this.
Wild Ginger has six inner stamens and six outer stamens, all of which produce pollen. In a newly-opened flower, all of these stamens lie flat against the “floor” of the flower. When the stamens are in this position, pollination is achieved by insects (often flies or beetles attracted to its rotten meat coloring and scent) as the pollen cannot reach the receptive stigma on its own. Wild Ginger hedges its bets, however. Whether or not pollination occurs early in its development, later in the life of the flower both inner and outer stamens move into an upright position, thereby moving closer to the stigma. Because the flower is oriented downward, this change in the position of the stamens allows for the pollen to fall onto the stigma, thereby accomplishing self-pollination. With or without pollinators, Wild Ginger succeeds in producing seeds.
Paper birch (Betula papyrifera) produces separate male and female flowers on the same tree, both in the form of catkins (cylindrical clusters of flowers). The catkins form in the fall and overwinter in a dormant state. In the spring they mature as the leaves develop, becoming pendulous. Male catkins are 2-4 inches long, whereas female catkins are usually 1 – 2 inches long. Both lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.
The female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts (yesterday’s blog post) and are usually dispersed by the wind during the fall and early winter. Birch bracts are species-specific — different species of birch have different-shaped bracts, allowing one to identify the species of birch that a bract comes from.