A Bloom for Every Bee
by Carolyn Aita
One day over 140 million years ago, somewhere a tiny carnivorous Apoid wasp went hunting for spiders. Perhaps she was frustrated by the lack of prey on that particular day, or discovered that an alternative source of protein could be obtained from the pollen grains of flowering plants that were emerging on the prehistoric landscape. We will never know what caused her to assert, “I’m done eating animals, I’m going vegan.” And so we have our very first bee.
Bees and the flowering plants that nurture them coevolved. Fast-forward to the present. During the 2022 flight season, I participated in WiBee, a citizen scientist activity that studies bees foraging specific plants. Monitoring the bees in my garden, I was amazed to find that these beautiful creatures come in many sizes and shapes. And the plants from which they seek nectar, pollen, and floral oil accommodate their diversity.
The flat flower heads of the plants in the aster family give all manner of foragers a landing pad, easy access to the nectaries where nectar is kept, and a place to rest between snacking (see The Sunflower Tribe, BDLIA Newsletter January 2023). Look at these green sweat bees covered with pollen while foraging on woodland sunflowers (A) and mistflowers (B). Factoid: There are nine species of sweat bees in Wisconsin, so named because they are attracted to the salt in human sweat. The species in (A) is Agapostemon virescens and it’s a gal. How do I know? She’s got black and white stripes on her back, which would be black and yellow for a guy.
Other plant families sport tubular blooms that do not flash their nectaries and therefore may present more of a challenge to a forager intent on getting the sweet stuff. It takes a big gal to pry open the tough flower of wild white indigo to get to its nectaries, but a two-spotted queen bumble bee is up to the task (C). Worker bumble bees have easier jobs crawling into the more pliant tubular flowers of smooth penstomen (D) and obedient plant (E). But what’s that other little guy on the obedient plant up to? A possible nectar thief! These robbers never enter a bloom. From the outside of a flower’s base, they bite holes to access the nectaries and lap up the nectar. Nectar thieves don’t aid pollination. Here’s why. Pollen is stored on anthers. In many tubular flowers, such as those shown in (D) and (E), the anthers are inside the tube structure. Since nectar thieves don’t enter the flower, they don’t brush against the anthers to release pollen, and hence they don’t carry pollen away to pollinate the next flower they visit.
In short, nectar thieves cheat plants with enclosed anthers out of pollination events. Not nice.
But some plants get around this problem. Consider Culver’s root in which the anthers are held on long filaments that extend outside of the lips of the tubular blooms (F). Visitors, such as the bumble bee in (F), can’t avoid contact with the pollen-laden anthers. In effect, this plant is informing all foragers, “There is no such thing as a free lunch here. You land on me, you carry away pollen.” But it’s win-win. Pollen is needed by bees for protein, fat, and other nutrients. Culver’s root’s unique anatomy makes pollen accessible to bees of all sizes and shapes. And there’s no need to rob nectar from this plant. The flowers, although tubular, are small and shallow enough so that even short-tongued bees can access the nectaries at their base.
This discourse gives a taste what can be found in a flower garden that has been planted for pollinators. Spring will soon be here and so will our native bees. I encourage you, gentle Reader, to see for yourself (once weather permits) that there is indeed a bloom for every bee.
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Photos by Mike Aita
WoodlandSunflower.JPG)
Mistflower.JPG)
WildWhiteIndigo.jpg)
SmoothPenstomen.jpeg)
ObedientPlant.JPG)
Culver'sRoot.JPG)
