A bee in the bonnet

For the past couple of weeks, most of the open areas around my apartment have been carpeted (somewhat treacherously) with the Texas state flower -- the bluebonnet.

A field of Texas bluebonnets (Lupinus texensis) and a few other flowers too.

Although the bluebonnets themselves are innocuous, they have been attracting swarms of both honey bees and photo-op seekers.  While watching the former and trying to ignore the latter, I noticed that the bluebonnets are remarkable for more than just their vibrant color.

A honey bee (Apis mellifera) approaches a bluebonnet.

Each flower is blue with either a white or a purplish inner spot; however, the color of the spot is not random.  Only the youngest flowers, those at the top of the spike, have a white center.  As the flowers age, their spots turn purple, similar to how the markings on horse chestnut flowers change from yellow to pink (and likely for the same reason). 

A honey bee collecting nectar.

The structure of the bluebonnets is also impressive.  The actual reproductive parts are all hidden away inside the flowers, so how does pollen get picked up and deposited?  Unlike the bees that I have seen squeezing inside some other lupine flowers, a honey bee visiting a bluebonnet just lands on top of the flower.

When the honey bee lands, the flower opens, exposing the stigma and anthers.

The weight of the bee then pushes the flower open.  In the process, pollen from the flower's anthers is rubbed onto the bee and pollen from the bee may get stuck to the flower's stigma.  The flower stays open for a moment after the bee leaves, then snaps back into place until the next visitor arrives.