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Working stiff

The lifespan of a honeybee is about five to seven weeks. In a healthy colony of around 50,000 bees, an average of 1,000 bees die daily. The bees at the beach are middle aged or elderly. We know this because an age-related division of labor occurs among most social insects. Worker bees nurse the brood and tend to the hive until they are two or three weeks old, and then they begin foraging.

Bees literally work themselves to death. If they do not fall victim to one of the many hazards of being a bee, such as predation or disease, they die after wearing out their wings logging hundreds of miles searching for flowers and lugging nectar and pollen back to the hive.

Compounding the normal bee mortality is an enigmatic disappearance of bees. In October 2006, U.S. beekeepers began reporting large losses of bee colonies. Symptoms exhibited by the affected hives did not match those produced by known bee parasites and diseases. The name Colony Collapse Disorder (CCD) was coined to describe the sudden losses, which have since been documented in many other countries.

Four main symptoms are associated with hives that have been lost to CCD. First, adult bees are absent. Second, few dead worker bees are found within or surrounding the hive. Third, the brood is still present. Fourth, food stores remain and are not scavenged by bees from other colonies or common colony pests.

Of the long list of possible CCD causes, most attention is on three: infectious agents, pesticides, and stresses related to bee-management practices. The strongest evidence to date, from a recent study of 91 colonies in 13 different apiaries in Florida and California, implicates infectious agents but does not rule out other causes.

The study found that CCD colonies had higher levels of viruses and were infected with a greater diversity of viruses than non-CCD colonies. Also, the distribution of CCD colonies was not random. Dead colonies tended to neighbor other dead colonies, suggesting that the condition is contagious. Because bees live in crowded conditions with genetically similar individuals, new diseases and parasites spread quickly.

No single disease distinguished CCD and non-CCD colonies in the study. Other studies have found specific diseases—including Nosema ceranae, a fungus that attacks cells in the gut, and Israeli acute paralysis virus—that are more common in collapsing colonies. It is not clear whether the diseases caused the collapse, but one way that bees control spread of disease is to have infected individuals leave the hive.

Many factors can reduce bees' disease resistance. For example, parasitic mites, which feed on bee blood, weaken their hosts and transmit disease. Recently, the mites have been evolving resistance to the most effective chemicals used to control them.

In addition, foraging bees are exposed to myriad pesticides intended for other insects. France banned one insecticide thought to be particularly harmful to bees, but colony losses have continued. Beehives are also being trucked greater distances than in the past, typically to less diverse food sources. Bees are often fed pollen substitutes and corn syrup in the winter, which may harm their health. The general consensus is that CCD is the result of this perfect storm of factors working in combination.

Although most of the workers you observe dying away from the hive are likely the result of normal population turnover, because of the sheer number of bees that involves, some may be from collapsing hives. For example, one of the symptoms of infection with Israeli acute paralysis virus is disorientation. Likewise, certain pesticides have been found to cause learning and memory problems in bees. Disorientation and memory problems could leave bees stranded on the beach.

Sea spray is another hazard for bees, especially on cold days. Evaporative cooling chills the bees, and bees need to keep their flight muscles warm to fly. Bees quickly rescued from our swimming pool usually fly off after drying in the sun and shivering to warm their flight muscles. But the rescue attempt fails if the bee is disoriented or injured, or stings its potential rescuer.

Beekeepers have long had to contend with "disappearing diseases," especially after harsh winters. Nonetheless, CCD has created quite a buzz because bee pollination is so important in agriculture, adding an estimated $15 billion in improved quality and yield of U.S. crops annually. The recent declines exacerbate a beekeeping trend that has more than halved the number of U.S. hives to 2.4 million during the past half-century.

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