The Schmidt sting pain index is a pain scale rating the relative pain caused by different hymenopteran stings. It is mainly the work of Justin O. Schmidt, who was an entomologist at the Carl Hayden Bee Research Center in Arizona.
Schmidt's original 1983 paper was a way to systematize and compare the hemolytic properties of insect venoms. A table in the paper included a column that rated sting pain, starting from 0 for stings that are completely ineffective against humans, progressing through 2 for familiar pains such as those caused by common bee or wasp stings, and finishing at 4 for the most painful stings. Only the bullet ant, Paraponera clavata, was given a rating of 4, although later versions of the index added two more species.
Schmidt repeatedly refined his scale, including a paper published in 1990, which classifies the stings of 78 species and 41 genera of Hymenoptera, and culminating in a book published in 2016.
Motivation The Schmidt sting pain index arose from the pursuit of a larger hypothesis: that the evolution of sociality in Hymenoptera was dependent on the evolution of venom that was both painful and toxic. Pain is a signal of damage in the body, but molecules that produce pain are not the same as toxic molecules, which actually cause damage. Although the painful signal acts as a deterrent, intelligent predators learn the dishonesty of this signal with repeated exposure. For the early Hymenoptera that were primarily solitary, the pain alone would allow them the chance to escape. Moreover, solitary insects do not provide a high energy reward for predators, and therefore predators do not expend significant effort to hunt them.
However, colonies of Hymenoptera are a nutritionally rich target. If there were no defenses, predators would devour the defenseless society, leaving few surviving individuals. Therefore it was theorized that the development of toxicity in Hymenoptera facilitated the development of sociality, which brings various benefits, including the shared raising of young, individual task specialization, inter-colony communication, and food storage. Assays for toxicity were already well characterized, so the evolutionary connection between toxicity and sociality could be studied. Schmidt developed his pain index to relate the amount of sociality to the level of pain.
Development Schmidt developed the index from observations made during his research on Hymenoptera and their venoms. He recorded the pain produced by around a thousand stings from more than 80 groups of ants, bees, and wasps, using his own experiences as the main comparison basis. He used the sting of the western honey bee (Apis Mellifera), a familiar and moderately painful sting, as a reference point with a rating of 2. Other stings were then given relative ratings on a scale from 0, for stings ineffective against humans, to 4, for the most painful stings. Schmidt also obtained ratings from colleagues to compare with his own scores.
These ratings were intended to make sting pain comparable for ecological and evolutionary research instead of giving clinical measures of pain. Schmidt uses the index with toxicity data to see whether greater pain and venom toxicity were associated with the evolution of sociality in Hymenoptera.
Scale summary Schmidt's pain scale of Hymenopteran stings is organized into levels, ranging between 1 and 4, with 4 being the most painful. However, insect stings that feel very different can be put into the same level. Thus, later versions of the scale always include a brief description of his experience being stung by each type of insect.
Level 1Some of the insect stings Schmidt considered to be at a pain level of 1 include the Southern fire ant, the graceful twig ant, the Western paper wasp, the urban digger bee, and most small bees. The duration of the pain of insect stings categorized into Pain Level 1 generally is five minutes or less.
Many small bees are categorized into a pain level of 1, with their venom containing polypeptides such as melittin, apamin, and MCD peptide. Melittin is the main toxin of bee venom, and it damages red blood cells and white blood cells. Apamin is a neurotoxin that augments polysynaptic reflexes. MCD peptide destroys mast cells.
Feeling only slight pain, Schmidt described the sting of an urban digger bee, categorized into pain level 1, as "almost pleasant, a lover just bit your earlobe a little too hard." Also rated into pain level 1, Schmidt has described the sting of a sweat bee as "light, ephemeral, almost fruity. A tiny spark has singed a single hair on your arm."Level 2Schmidt set the sting of the Western honey bee at a pain level of 2 to be the anchoring value, basing his categorization of all other stings on it. He has categorized a variety of wasps, bees, and ants into pain level 2, including yellowjackets, the Asiatic honey bee, the trap-jaw ant, and the bald-faced hornet. The duration of the pain of the stings in this level is generally between five and ten minutes long. Schmidt categorized the majority of Hymenopteran stings as having a pain level of 2.
The sting of a termite-raiding ant, categorized as a pain level of 2, has a similar feeling as "the debilitating pain of a migraine contained in the tip of your finger," according to Schmidt. A yellowjacket's sting was described as being "hot and smoky, almost irreverent. Imagine W. C. Fields extinguishing a cigar on your tongue." He also described the sting of the honeybee as a similar feeling to "The oven mitt had a hole in it when you pulled the cookies out of the oven."Level 3Most insects that are characterized as having a pain level of 3 are wasps, including the neotropical red paper wasp, the red-headed paper wasp, and Klug's velvet ant (a wingless wasp and not a true ant). The duration of the sting pain can range anywhere from one minute (such as the sting of the red paper wasp) to half an hour (such as the sting of the velvet ant). Wasp venom uniquely contains kinin. One of the kinins found in wasp venom, "polistes kinin 3", is found to lead to similar effects on smooth musculature and circulation as bradykinin.
Some ants are also rated at a pain level 3, including the giant bull ant and the Maricopa harvester ant. Schmidt considered the sting of the Maricopa harvester ant to have a pain level of 3, describing it as such: "After eight unrelenting hours of drilling into that ingrown toenail, you find the drill wedged into the toe."Level 4The highest level in the Schmidt sting pain index. Schmidt's original index rated only one such example, the sting of the bullet ant Paraponera clavata, as a 4. He wrote, "Paraponera clavata stings induced immediate, excruciating pain and numbness to pencil-point pressure, as well as trembling in the form of a totally uncontrollable urge to shake the affected part." In a later work, he described the sting as "pure, intense, brilliant pain...like walking over flaming charcoal with a three-inch nail embedded in your heel." The bullet ant's venom primarily contains poneratoxin, a paralyzing neurotoxic peptide.
He later gave the sting of a tarantula hawk species, Pepsis grossa, a rating of a 4, which he described as "blinding, fierce [and] shockingly electric", though the duration of pain from the sting is short-lived, lasting only approximately five minutes. The composition of tarantula hawk venom is unknown.
He also later rated the sting of Synoeca septentrionalis as a 4, describing it as "Torture. You are chained in the flow of an active volcano. Why did I start this list?", saying the pain lasts up to two hours.
Entire scale Schmidt's entire list of ratings and descriptions: