Mr. Riley and Mr. Wilson buttoned their shirt collars snug against their necks (to keep bugs from falling in), slipped on thick neoprene gloves, laced up their snake-proof boots and turned on the big black lights they each carried.

Scorpions glow under black lights. The glow comes from a substance found inside a hard-and-thin coating on the scorpion’s exoskeleton. Scientists are not sure what purpose it serves. Some say it is to confuse prey; others believe it is to protect scorpions from sunlight.

There are 1,800 types of scorpions in every place on the planet except for the Arctic, and more than 50 species in the Sonoran Desert, which covers much of the state. At no more than three inches long, bark scorpions are the smallest, most common and most dangerous — “the only one of them considered to be life-threatening,” said Keith Boesen, director of the Arizona Poison and Drug Information Center, housed at the University of Arizona College of Pharmacy in Tucson.

On average, the center and its counterpart in Phoenix log 12,000 reports of scorpion stings each year, though many more go unreported because people treat them at home. Children, older adults and those who are infirm are particularly vulnerable and should seek immediate help if they get stung, Dr. Boesen said. Deaths are rare — there was one in 2013 and another some 10 years earlier, he said.

Still, pain and discomfort from a scorpion’s sting are inevitable and the reactions can range from scary to bizarre.