Bob's Brain on Botany --mid August 2009

Hooray for August, when we see Ptilothrix bombiformis, the ground-nesting solitary bee associated with rose-mallow (Hibiscus moscheutos) plants at Stage's Pond State Nature Preserve in Pickaway County, Ohio. Pertinent aspects of Ptilothrix natural history were described in August 2008. As mentioned then, the bees construct pencil-wide vertical burrows in the dry soil of a path through a meadow near a rose-mallow marsh along prepositional phrases. Although dozens of individual female bees construct their burrows side by side, these are still considered "solitary" bees because they are not social insects like ants, honeybees and bumblebees, whose queen is the only reproductive female and there are sterile "workers" who all live together. Instead, each Ptilothrix female builds her own little nest, and every individual has the capacity to reproduce. They simply nest in groups as do, say, cliff swallows.

Here's a snapshot of the nest area, with a person included for scale. He's watching the bees come and go, while conjuring up scientific hypotheses about them, that could be tested without harming the bees.

Ptilothrix nest site: a path through a meadow near a pond in Ohio. August 23, 2009.

In March I acquired a nifty new camera: the Canon EOS 5D Mark 2. This is a digital single lens reflex (DSLR) camera with a new feature that is likely to become standard on DSLR's: the capacity to shoot video. This is good because it eliminates the need to lug around a whole other camera just in case a subject turns up that's well suited for video. Also, DSLR lenses come in many sizes, enabling macro or telephoto videos that would be impossible using a consumer-grade camcorder, or even the current generation i-phone. (Just wait though. And expect a Ptilothrix "app.") Shooting video is great fun.

Canon 5D Mark 2 --good for stills and video!

The hibiscus bee moves around a lot and isn't very camera-shy --she was made for movies!
Here's a video of the "bee city."

As swamp cicadas sing, Ptilothrix females come and go to and from their nests.
Stage's Pond State Nature Preserve. Pickaway County, Ohio. August 14, 2009.

Here's an aerial view of a "neighborhood" of "bee city." Note how the bees quickly and inconspicuously enter and leave their burrows. At 3 minutes and 10 seconds into the clip, a notably plump, yellow one can be seen bringing pollen home. (Discussed further below.)

Ptilothrix nesting area at Stage's Pond. August 7, 2009.

Here, a bee initiates nest construction by digging into the soil of a grassy path.

Ptilothrix starts a new burrow at Stage's Pond. August 14, 2009.

Athough I've never observed it --Stage's pond is quite large and ca. 100 meters from the nest site --hibiscus bee is famous for standing water-strider-like on the water's surface and drinking water from it, then flying home and using the just-sipped water to moisten, and thereby soften, the soil she is burrowing into to place her nest. In the video below, observe how the soil becomes wet (dark) as she works it with her mouth.

As a rufous-sided towhee and common yellowthroat serenade, Ptilothrix
constructs a nest-burrow, moistening the soil with pond water sipped earlier on August 14, 2009.

The most dramatic thing the hibiscus bee does during nest construction is to toss little balls of excavated soil away from the burrow using her hind legs. The following gallery shows pictures taken about 1/8 second apart. A dirt-ball is image-captured in mid-air.

Slideshow of Ptilothrix kicking soil out of her burrow.

Here's a short video of the same thing.

While a song sparrow sings, Ptilothrix kicks soil out of her burrow. August 7, 2009.

...and here's a somewhat longer one. In the beginning, she seems to be having trouble with a pesky pellet!

Ptilothrix pushes pesky pellet. August 7, 2009.

At another stage of construction, the bee moulds a chimney-like turret about the entrance hole by pushing moist soil upwards with her abdomen.

Ptilothrix moulds a chimney-like turret above her nest burrow. August 7, 2009.

Here's a closeup view.

Ptilothrix shapes the soil around the entrance to her nest burrow.
Musical accompaniment by song sparrow and field sparrow. August 7, 2009.

When burrow construction is complete, the hibiscus bee gathers pollen from rose-mallow flowers. In typical Malvaceae fashion, hibiscus flowers have a bottlebrush-like arrangement of numerous stamens attached along a tube that surrounds the style. The five stigmas are prominently placed in the flight path of an approaching bee.

Here's a video montage of the pollen-gathering process. Note that, in one of the instances, Ms. bee, on her departure from the flower, clambers all over the stigmas, no doubt effecting self-pollination.

Hibiscus bees gather pollen from Hibiscus moscheutos.
Stage's Pond State Nature Preserve, Pickaway County, Ohio. August 7, 2009.

After she's gathered enough pollen, and looking so cute --like a little yellow flying pop-pom --she makes a bee-line back home to sequester it away in the burrow. (Later she'll lay an egg on the surface of the ball.)

Here's a video of a bee dropping down into her hole. At the end of the segment, she leaves to get more. Not much happens in the interim. You might just scroll ahead to the amazing climax.

Ptilothrix delivers pollen, then goes off for more. August 14, 2009.

Often, as shown above, they drop straight into the burrow. But here's an instance of slight imprecision, where the bee lands some distance from her burrow, then crawls over to it and enters on foot as a song sparrow calls loudly.

Ptilothrix somewhat clumbsily enters her burrow. August 14, 2009.

Somehow the bees know which hole is theirs and avoid trespassing. Occassionaly a mistake is made. Here a bee at home is merrily digging and tossing dirt-balls. A second bee accidentally interlopes, then instantly retreats. Apparently non-plussed, the rightful resident proceeds with her construction project.

A Ptilothrix bee briefly enters a neighbor's borrow, apparently by mistake.
Stage's Pond State Nature Preserve. August 7, 2009.

Apparently, misunderstandings about residency are not always quickly resolved. Below, two Ptilothrix females engage in direct conflict over who belongs there. They alternately enter and then get dragged out by their adversary. Yikes!