It started when a honeybee flew up Michael Smith’s shorts and stung him in the testicles.

Smith is a graduate student at Cornell University, who studies the behaviour and evolution of honeybees. In this line of work, stings are a common and inevitable hazard. “If you’re wearing shorts and doing bee work, a bee can get up there easily,” he says. “But I was really surprised that it didn’t hurt as much as I thought it would.”

That got him thinking: Where’s the worst place on the body to get stung?

Everyone who works with stinging insects has their own answers, but Smith couldn’t find any hard data. Even Justin Schmidt was no help. Schmidt is the famous creator of the Schmidt Sting Pain Index—a scale that measures the painfulness of insect stings using wonderful synaesthetic descriptions that almost read like wine-tasting notes. Wine-tasting notes of agony.

According to Schmidt’s index, the sweat bee sting (1 on a scale of 0 to 4) feels like “a tiny spark has singed a single hair on your arm”. The yellowjacket sting (2) is “hot and smoky, almost irreverent; imagine W. C. Fields extinguishing a cigar on your tongue.” And the daddy of stinging insects—the bullet ant (4+)—produces “pure, intense, brilliant pain, like fire-walking over flaming charcoal with a 3-inch rusty nail grinding into your heel.”

Schmidt recognised that “pain levels from particular stings do, of course, vary and depend on such features as where the sting occurred (…)”, but he didn’t say how these levels vary by body part.

So, Smith decided to find out. His experimental subject: himself.

As he writes in his new paper (which, incidentally, is deadpan gold): “Cornell University’s Human Research Protection Program does not have a policy regarding researcher self-experimentation, so this research was not subject to review from their offices. The methods do not conflict with the Helsinki Declaration of 1975, revised in 1983. The author was the only person stung, was aware of all associated risks therein, gave his consent, and is aware that these results will be made public.”

Smith was methodical. He collected bees by grabbing their wings “haphazardly with forceps” and pressing them against the body part of choice. He left the stinger there for a full minute before removing it, and then rated his pain on a scale of 1 to 10. Pain is very hard to measure, but psychological studies have found that numerical scales do a decent job of putting numbers on an inherently subjective experience.

He administered five stings a day, always between 9 and 10am, and always starting and ending with “test stings” on his forearm to calibrate the ratings. He kept this up for 38 days, stinging himself three times each on 25 different body parts. “Some locations required the use of a mirror and an erect posture during stinging (e.g., buttocks),” he wrote. If you are chuckling at the image of a man twisting around in front of a mirror to apply an agitated bee to his butt, I assure you that you are not alone.

View Images Smith’s pain map. The scale is from 1 to 10.

“All the stings induced pain in the author,” Smith writes. The least painful locations were the skull, upper arm, and tip of the middle toe (all averaging 2.3). “Getting stung on the top of the skull was like having an egg smashed on your head. The pain is there, but then it goes away.”

The most painful sites were the penis shaft (7.3), upper lip (8.7) and nostril (9.0). “It’s electric and pulsating,” he Smith. “Especially the nose. Your body really reacts. You’re sneezing and wheezing and snot is just dribbling out. Getting stung in the nose is a whole-body experience.”

“Erm, but the penis?” I venture.

“It’s painful, and there’s definitely no crossing of wires of pleasure and pain down there,” he says. “But if you’re stung in the nose and penis, you’re going to want more stings to the penis over the nose, if you’re forced to choose.”

Was there any point in the experiment when he thought: Hey, maybe I shouldn’t sting myself in the nose and/or penis?

“By the time I got round to the third round, I thought: I really don’t want to do my nose again,” he says. “I had originally had the eye on the list, but when I talked to [my advisor Tom Seeley], he was concerned that I might go blind. I wanted to keep my eyes.”

There are some interesting nuggets here. We might expect that the most painful places to get stung are the sites that have the thinnest skin or that are served by the most sensory neurons. But neither factor cleanly explains the results. For example, palm with its thick skin hurt much more than the thin-skinned arm or skull. And the upper lip hurt much more than the middle finger, even though both are served by similar numbers of neurons. A pain map of the body would probably look very different to a purely sensory one.

Now, clearly, these data are very subjective, and they all come from one person. Smith is clear that his anatomy of pain can’t be generalised to everyone else. “If someone else did this, they’d probably have different locations that they felt were worst”, he says, although from talking to his colleagues, he feels that the rough shape of the map would be similar.

“I didn’t see a lot of merit in repeating this with more subjects,” he says.

Any takers?