The Crafty Carpenter Bee

CARPENTER BEES: BUILDING FOR THE NEXT

A good many Arizonans first become acquainted with carpenter bees when the jet-black insect almost as big as a Ping-Pong ball buzzes in, eyeball to eyeball, causing us to hop out of our patio chairs with remarkable agility. Although this response is understandable, given the intim-idating size of carpenter bees, actually the insects will not sting unless they are mistreated. The ones that zoom up to us prob-ably are females harmlessly looking for a nest site, not killer bees intent on attack. Aptly named, carpenter bees (and there are several hundred species worldwide) usually exercise their carpentry skills on woody items. Female carpenter bees use their powerful cutting mandibles to tunnel into wood. One Arizona species favors dead stubs of ironwood or mesquite (or a chunk of firewood). Another Arizona carpenter bee typically burrows into tough, dry agave or sotol stalks that have been dead for a while. The nest-building female gnaws out a tunnel as wide as it is and up to a foot or more in length. At the end of its nest tun-nel, the female places provisions for the first of several “bee breads” it will make of pollen and nectar. When it returns to the nest, the female bee removes pollen from its hind legs and regurgitates nectar from its honey crop, molding these substances into a moist yellow ball, which grows with each trip until it is nearly as big as the end of your thumb.The food mass will feed one larva when it hatches from the huge egg the female lays on the com-pleted bee bread. The grub survives on the bee bread while nes-tled within its cubicle, the outer end of which is sealed off with small bits of wood scrapings the female glues together with a salivary secretion. The mother bee then repeats the entire process several times until it has constructed a line of cells in its nest tunnel. Eventually the larvae will feast to repletion and then begin the process of metamorphosis that ends when they become adult bees. Newly adult carpenter bees use their jaws for the first time to chew through the partitions separating their cell from anoth-er while they make their way toward the nest exit. The bees somehow know, probably by the shape of the partitions between cells, which way to go when emerging. Furthermore, the whole process is nicely timed so that the bees in the inte-rior of the nest do not try to exit the tunnel until their siblings have safely left. Depending on the species, the newly emerged adults may return to and remain in their natal nest for some time. Eventually, however, some virgin females fly off to mate and build their own nests. Females of one Arizona species usually find a mate waiting for them outside the nest entrance. In this species, males fight for the right to hang around these established nests where they wait for hours each day for the rare chance to mate in the air with a receptive virgin female. Males of another Arizona carpenter bee species do not leave their natal nests to search for other nests with emerging virgins. Instead, for most of each day they stay with their sisters and mothers, which feed them regurgitated nectar. The males depart temporarily in late afternoon, heading to hill-tops or major washes where they establish hovering territories around prominent shrubs or trees. There they produce and release fragrant chemical compounds from a gland in the tho-rax. Unmated females appear to use the scent to locate males. They fly rapidly upwind along desert ridges or in washes before zigzagging in toward a hovering male. The male then turns to a small sprig of vegetation in its

Text and Photographs by John Alcock GENERATION

Creosote bush or ironwood tree and lands on the leaves repeatedly, stroking them jerkily with its legs. Often the females seem unimpressed and continue their journey, perhaps inspecting other males.

Sometimes, however, the female approaches the displaying male more closely and then lands on the very spot the male has been touching so agitatedly. Then mating occurs, after which the female drops from the perch, and the pair separate. The female flies off carrying all the sperm it will need during its lifetime. The male continues to hover by its station until dusk, when it returns to the care of its female relatives in the natal nest.

Thus it is not just their large size and fearless response to people that make Arizona carpenter bees worth getting out of our patio chairs for, but also their complex nesting and mating behavior, which add variety and drama to the natural history of the desert.

Editor's Note: To learn more about carpenter bees and other desert arthropods, contact Sonoran Arthropod Studies in Tucson. This nonprofit environmental-education organization offers public lectures, field trips, and hands-on workshops in addition to publishing a magazine, Backyard BUGwatching. For information, call or write: Sonoran Arthropod Studies, P.O. Box 5624, Tucson, AZ 85703; (602) 883-3945. John Alcock is a professor of zoology at Arizona State University in Tempe. He wrote Sonoran Desert Summer, published by the University of Arizona Press.