But what about stings that are only minimally toxic? “Pain, the experience of pain, is a body’s warning system that damage has occurred, is occurring or is about to occur,” Schmidt explained to me. “But pain itself is not the same thing as damage.” What about the tarantula hawk, a solitary wasp, whose sting is far more painful than that of a honeybee but leaves no lasting damage at all? That kind of barely toxic sting, it would seem, succeeds as a defensive strategy purely by inflicting pain. An understanding of a sting’s toxicity, in other words, didn’t entirely capture how a sting works as a deterrent.

To go any further, he realized, he needed to invent a language to talk about pain. Thus the Schmidt Pain Scale for Stinging Insects was born. Using his own field experience with stings, and occasionally supplementing it with the testimony of his oft-stung colleagues, he began to develop a scale, from 0 to 4; the sting of the honeybee, Apis mellifera, was set as the anchoring value, defined as a pain level of 2. The pain scale would allow Schmidt to draw comparisons, to test hypotheses and to help him document theories on the role of the sting in the natural history of insects.

The approach is hardly scientific. His sample size was tiny. The scale wasn’t based on solid controls of variables, like the age of both insect and predator or the placement of the sting on the body of the victim. Even under the best of circumstances, pain is notoriously difficult to gauge; reliable methods for measuring nerve responses of pain were, and remain, imprecise.

But the pain scale was a useful start. As a tool, it has helped Schmidt explain a major hypothesis: that the adaptation of highly toxic stings was critical in helping insects transition from a solitary existence to one structured by advanced social orders, what is known as eusociality. Early insects lacked toxic stings because, as low-value prey, they didn’t need them. What those solitary insects did have — and their contemporary descendants, like tarantula hawks, still have — was a powerfully painful sting, which functioned defensively by inflicting pain on predators. Later in history, around the time insects began organizing into complex societies, they upgraded their defenses. Social insects’ colonies are stocked with tender and nutritious larvae and sometimes also honey, offering a high-value target, which meant they had to evolve to repel more highly motivated predators. So they began selecting for stings that were not just painful but also potentially lethal. Or, as Schmidt, sitting in his lab sipping his iced tea, put it, the sting pain of the social insect “delivered more than just an advertisement — it told the truth.”

When I met Schmidt in Tucson, I had just returned from an expedition into the Sonoran Desert of Mexico with a large group of field biologists. Schmidt had pulled out of the expedition because of the flu. Initially, I was disappointed that he couldn’t make the trip — I’d been curious to see him prowling the Chihuahua pines with his net, excavating harvester-ant colonies. But I discovered that Schmidt’s absence yielded its own insights; without him around, his colleagues were free to gossip.

“Oh, Schmidt?” said Bob Johnson, an ant specialist with a Bill Murray vibe. “Now there’s a case for you. I’d say maybe that guy’s been stung one too many times.” John Palting, a moth expert, who descended from his campsite every morning with an exquisite collection of specimens that he pinned the night before, laughingly recalled watching Schmidt at work in the field. “You’d do a double take,” Palting told me. “You’d walk by him, and he’d be doing this,” Palting made a gesture as though stabbing himself repeatedly in the wrist, “and you’d say: ‘Dude! Take it easy. We’re in the middle of nowhere here. If you have a bad reaction to that, I’m not carrying you out of here.’ ”