Wednesday, March 27, 2013

Desert Bees

We have a collection of early spring bloomers in our backyard, a mix of imported and native species. Right now, there are several penstemon species, aloes, creosote and brittle bush in full bloom.

Parry's Penstemon is a native species. It can be found in many sandy washes of the Tucson Mountains and beyond. In our garden it is blooming in direct vicinity of several showy Aloe species.

The imported Aloes attract the equally imported Honey Bees, and birds who are not very fussy when it comes to sweet juices.

 Hummingbirds, Gila Woodpeckers and Orioles are frequent visitors. But the native Parry's Penstemon is visited by local specialists.

Habropoda  and Anthophora Bees hover from flower to flower, land, and are gone again. Every flower seems to yield  only a very small amount of nectar. This makes life difficult for macro-photographers, but even more so for the bees.

This becomes obvious when the sun disappears shortly behind a cloud resulting in an immediate drop in temperature. Some bees keep going and going. But others soon drop out of the race for nectar. They clamp their mandibles on a leaf or a stem, tuck their legs and rest motionlessly. I can see that they do not carry any loads of pollen, and when one finally starts moving again I see a flash of white from the face: the bees that take brakes seem to be all males. They may stop flying when the temperature drops and they would have to spend extra energy on heat production to keep their flight muscles operative. For males this expenditure may not be worth it. The resting individuals also looked old and ragged. Maybe they have done their duty.

The pollen loaded females who are provisioning their nests seem to have reasons to invest more energy and keep flying, at least at our only slightly sub-optimal temperatures. 
 Habropoda  and Anthophora are Anthophorine Bees with very long togues (0.4 to 0.8 inches) that enable them to pollinate deep flowers (O’Toole & Raw 1999). Adapted to both temperate and tropical climates Anthophorines are wide-spread, but in the US most abundant in the West and Southwest. They are called mining bees because they are solitary ground nesters whose females dig tunnels in the soil to accommodate a series of brood cells. The cells are lined with an oily substance for protection against moisture and fungal infections.

While watching the bees for hours on several days I saw very few honey bees visit the Penstemon, but quickly return to the aloes. The native Habropoda  and Anthophora Bees completely ignored the aloes and concentrated on just one species of penstemon and the surrounding creosote bushes. Every evening, when it's too cool for most bees, a big female Carpenter Bee also harvests pollen from the creosotes. I will have to use a flash to get her photo.

See also:
The Great Sunflower Project, Anthophora – mining bees (family Apidae)
by Lisa Schonberg and Mace Vaughan (Xerces Society) and Gretchen LeBuhn (SFSU)


  1. Looks like you've got the Hooded Orioles -- they are just now invading San Diego County, too.

  2. I wonder... Do you think it's the temperature or the drop in light intensity that causes the bees to stop moving? I did a project with damselflies as an undergrad that showed that although temp did cause a bit of a drop in flight activity prior to storms, the light intensity was a much stronger factor in the behavior. I think that the damselflies use the light as a cue to roost, so they disappear from the ponds prior to storms and fly away to their roosts, then return once the light picks back up (thereby avoiding the storm entirely). Wonder if your bees might be doing the same thing!

  3. Great comment, helps me to point out an important difference between bees and dragonflies: Bees are not completely exotherm, dragons are. Bees can shiver and actively increase their body temps, but it costs them. Bernd Heinrich found that bumblebees in areas with flowers that yielded high caloric nectar would keep feeding and flying (fireweed) whereas those in areas with low yield goldenrod sat down, crawled on the flowers but didn't fly. He took temp measurements and the fireweed ones were high above ambient (they could afford it). My bees were all on the same plant and I couldn't measure temps, but I just speculate that the females were more motivated to keep going. By the way, they were all not hiding before a storm, they just took little breaks when it got temporarily colder. But you know the desert: one can feel every little cloud shadow imediately