Bees

Desert Bees Let sleeping Idiomelissodes duplocincta lie

Text and photographs by John Alcock At 7 P.M. it was time to check on the bees. I left my air-conditioned desert home and headed out to my superheated front yard. Sure enough, the bees swirled about a brittlebush, just as they had for several weeks during the summer. A great many bees had already settled down, using their jaws to grasp the long, dried flower stems sticking straight up from the crown of the brittlebush. As the sun sank below the roofline of the house next door, the last bees bumped and pushed their way onto a bit of stem. By the time all was still, 300 or so insects crowded onto about a dozen stems where they would sleep quietly through the night.

Mention bees, and most people think of the honeybee, several races of which (one being the notorious Africanized "killer" bee) have been imported by bee geneticists or beekeepers into the Americas. But those sleeping in my front yard did not make honey; they belonged instead to the large coterie of genuinely native bees, some of which pollinate the brittlebushes, fairy dusters and paloverde trees in my yard and throughout the desert.

Most bees native to the United States differ in many ways from the foreign honeybee. Take my sleeping bee, Idiomelissodes duplocincta, for example. Although it has a long Latin name, this bee averages just a third of an inch long, less than half the size of the honeybee, and each female nests by herself rather than in a hive with thousands of others under the control of a queen. Each little female digs a tunnel into the hard desert soil, then fashions a series of side chambers into which she deposits pollen and nectar taken from flowering cacti. The egg that is laid in each fully provisioned chamber hatches into a grub that will consume the food provided by its mother. Eventually, the grub will become an adult, which then gnaws its way to the surface and escapes into the desert air. Newly emerged females soon meet and mate with males, which spend their days searching for partners. When, however, no receptive females can be found, and nesting females have already crawled inside their burrows to sleep safely underground, males seek out the company of their own sex and then kick and push their way into rows, like the ones on my brittlebush.

Why do males go to the trouble of getting together in the evening? Having had the good luck to attract an Idiomelissodes male sleeping club, I was eager to answer this question, so I spent many summer evenings marking males (which do not sting) with tiny dots of paint. I determined that some individual bees return to the cluster night after night. As I scanned the aggregation for marked males, I also discovered the sleeping clusters are occasionally visited by one orScientists speculate that the male Idiomelissodes duplocincta common in Arizona may prefer flowers as communal roosting sites when a female begins to gather pollen.

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Bee alert: As evening approaches, males of the species know it's time for a sleep-over with the guys.

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Clutching their perch in their jaws, the small desert bees cluster together on a few dried flower stems for nocturnal protection.

Two assassin bugs. This aptly named predator uses its strong, grasping forelegs and long, curved beak to grab and stab its unlucky prey. The bug injects toxins and enzymes to kill the victim and digest its internal organs, which are then slowly taken up by the assassin bug through its lethal proboscis.

The assassin bugs that came to the sleeping cluster in my yard were not attacked by the male bees. Indeed, the bees generally ignored the bugs grappling with a soon-to-be-deceased companion just behind or in front of them. So the bees do not form groups to better repel or detect and evade incoming predators. Instead, the bees apparently sleep together merely to dilute the risk of becoming an assassin bug's meal. Because the bugs can kill and consume only one or two prey per evening, bees that gather in a group of 300 have only one or two chances in 300 of having fatally bad luck. In groups of 30, the risk per individual jumps tenfold. Thus, the males' modest social behavior has the effect of increasing the odds that an individual will survive the night to have one more day of searching for mates.

Each year I look forward to the formation of the sleeping clusters of Idiomelissodes and so do several city friends who also have installed Sonoran Desert plants in their yards. At my place, new generations of males always select the same large brittlebush for the communal boudoir, which provides me with the company of true Arizona natives year after year. I am grateful to both the plant and the bees for making discovery possible right out the front door. AH John Alcock is Regents' Professor of Biology at Arizona State University in Tempe and a longtime observer of desert insects.