On a late May morning a pair of young hikers were walking along a popular desert trail near Mesa, Ariz., when they heard the buzzing of honeybees. The hikers, Alex and Sonya, were unaware that they had happened upon an extraordinarily large hive, which experts later estimated contained about 50,000 Africanized honeybees. The bees gather nectar from the carpet of wildflowers that covers the desert floor, peaking in May and June, supporting colonies that quickly grow from a few thousand individuals to 10,000 bees or more.

The bees would not have begun stinging immediately, according to Carl Olson, an entomologist at the University of Arizona. “Honeybees are pretty good at warning people away,” he says. “Just as a rattlesnake will vibrate its tail as a warning, the first honeybees out of a hive will bump the person invading, saying ‘Leave!’.”

Sonya, who lived and often hiked in the area, had moved farther down the trail and took off running. But Alex, a visitor from North Dakota, may have swatted the bees. Swatting is a natural human reaction, but arm-waving and slapping at bees can turn a chance encounter into an attack, says Justin Schmidt, an insect behaviorist at the Tucson-based Southwest Biological Institute and author of the recently published book, The Sting of the Wild.

“Bees don’t form images in the same way that humans do,” he explains. “They use vision primarily to detect motion, and quick or jerky movements near a nest are interpreted as a threat.” The bees respond by stinging, injecting a venom consisting primarily of the peptides melittin and phospholipase.

Once embedded in the skin stingers also release tagging pheromones, potent chemical signals that attract and arouse other bees. When released near a colony, these pheromones can provoke a massive defensive swarm from the females guarding the nest. “The chemical signal says, ‘Here, sisters, here is where I found a chink in the armor of this big attacking predator,’” Schmidt says. “It really arouses them.”

Running and taking cover inside a park restroom probably saved Sonya’s life. But her friend wasn’t so fortunate. Rescuers found Alex on the ground near the hive, covered with bees. He was rushed to a nearby hospital but the young man soon succumbed to the toxic effects of more than 1,000 stings.

Following the tragedy, the local sheriff told reporters “these attacks are becoming more frequent.” That’s possible, Schmidt says. After all, cities are expanding into previously undisturbed areas and more people are out hiking than ever before. But, as Schmidt points out, claims that mass envenomations—the technical term for large-scale bee attacks—are on the rise are purely speculative. “No one is keeping track,” he says. “We simply don’t have databases with that kind of information.”

The threat from Africanized honeybees has been exaggerated since the European-African hybrids escaped from hives in Brazil in the 1950s, reaching Texas three decades later and spreading throughout the Southwest, where the hot, dry conditions allow them to thrive. Investigators first thought that an Africanized honeybee sting was more lethal than that of other bees. But in 1989 Schmidt co-authored a study in Nature that found no difference in the lethality of the venom from various honeybee subspecies. The authors concluded: “Perhaps use of the popular term ‘killer bee’ to describe the Africanized bee is inappropriate.”

Although fatal encounters with hikers are extremely rare, Schmidt has a few simple suggestions to ensure safe hiking in areas where bees are likely present:

Wear light-colored clothing. Honeybees have evolved to recognize threats from predators like bears, honey badgers and other dark-furred mammals. Also avoid the color red, which appears black to bees.

Never approach or disturb a nest. If you notice bees entering or exiting a rock crevice, a hole in the ground or a tree cavity, assume there’s a nest present and leave the area immediately.

Pay attention to bee behavior. If bees fly into you or begin to swarm over or around you, they are probably trying to warn you off. Remember: don’t swat at the bees, just leave.

If you accidently disturb a nest, run immediately. Try to get to an enclosed shelter (such as a car) or run until the bees stop following you. It may be necessary to get a quarter mile or more away from where the attack began. Cover your face with whatever is handy, if you can do so without impairing your vision.

Never jump into a body of water to escape bees. They will wait for you to surface. Schmidt points to a case in which a swarm of bees hovered for hours over a man in a lake, stinging him whenever he came up for air. (The man survived only because the bees returned to their hive after sunset.)

Schmidt warns that some commonly seen tips for avoiding bee attacks may appear reasonable but have no scientific basis. “You often read things like ‘avoid floral-scented perfumes and deodorants,’ but that’s a bunch of malarkey,” he says. “The primary sensory modality for insects is odor but there is absolutely no experimental evidence that smelling like a flower attracts bees.”

Fortunately, avoiding potentially dangerous interactions with bees is straightforward. “Just be sensible for heaven’s sake,” Schmidt advises. “Pay attention to posted warnings. Wear light colors. And if you see bees, get away from them.”