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The Sting of the Wild

Page 15

by Justin O. Schmidt


  D. L. Wray in 1938 described his sting reaction to a Florida harvester ant this way: “It turned deep red in color and immediately a watery, sticky secretion came out of the skin. It beaded out like heavy perspiration and ran down my arm. This area became hot and feverish and the excruciating pain lasted all day and up into the night.”29 Creighton in his classic 1950 “Ants of North America” writes matter-of-factly “the sting of most species of Pogonomyrmex is exceedingly painful. It is not a localized reaction, like that of a bee sting, but one which spreads along the lymph channels and often causes intense discomfort in the lymph glands of the axil or groin long after the original pain of the sting has ceased.”1 Arthur Cole in the introduction to his 1968 Pogonomyrmex Harvester Ants detailed a sting: “The effect of a sting can be very painful. Localized swelling and inflammation ensue rapidly. Soon thereafter a throbbing pain, which may last several hours, extends to the lymph nodes of the inguinal, axillary, or cervical area, depending on the location of the sting. Frequently, the skin around the wound becomes very moist.” Finally, the great husband and wife team of George and Jeanette Wheeler wrote in 1973:

  [The author was] stung on middle of free edge of upper lip. The ant was knocked off promptly … [the] pain did not begin for ten minutes—a general burning sensation. After an hour a dull ache commenced in the lips, the incisor teeth and the adjacent jaw. The middle third of the lip was slightly swollen and slightly red. … Six hours after the sting the ache had subsided to be followed by a burning sensation in the upper lip. The next morning (ten hours after the sting) there was a diminished burning sensation in the middle 55 mm of the free edge of the lip, which was edematous but not reddened; the middle 10 mm of the 55 mm was insensitive to touch. After 12 hours feeling began to return but the free edge was still numb, slightly swollen and with a slight burning sensation. After 24 hours the swelling was scarcely visible but the lip felt tight. There was no pain. … Two days after the sting the inner surface was hypersensitive and felt hot when rubbed. … Twenty-six days after [the] sting the middle section of the lip was still hypersensitive to touch.30

  From these descriptions, we see that nobody who is ever stung by a harvester ant is unaffected, and the consensus is that these stings are remarkable in more ways than we wish to repeat.

  Harvester ant stings differ from those of all other known insect stings in at least five ways. First, and to the victim’s disadvantage, is the lack of an instantaneous reaction to the sting. No lightning bolt of pain, no fiery ember burning the skin. Rather, a somewhat delayed reaction before the pain is noticed and then the inexorable increase in pain. How long this initial “painless” period lasts after insertion of the sting is hard to know because if we do not realize we are being stung, we cannot start the stopwatch. When we do notice, it is too late; the damage is already done. My feeling is that the unnoticed period, at least for stings to the feet or legs, is about 30 seconds. How does this delay in pain benefit the harvester ant? After all, isn’t it to the ant’s benefit for the pain to be immediate? The answer might reside in short-term versus long-term benefit for the ant and her colony. The ant’s venom injection system is rather slow. Thus, if instantaneous pain were produced at the very beginning of the process, the victim could remove the ant and quickly stop the damage. However, if a delay in pain occurs, then the ant can deliver a richer, fuller dose of venom to maximize long-term damage.

  A second difference between harvester ant stings and other stings is the localized sweating induced around the sting site. The sweating seems more viscous and sticky than usual sweat and does not occur anywhere else on the skin. This sweating is easily detected by gently moving a finger from side to side across the sting area. The finger glides smoothly and easily over the nonsweaty area, then encounters a friction in the sweaty area, and finally returns to gliding smoothly and easily again. To make the test more sensitive, I sometimes use my upper lip instead of a finger. No other insect sting causes sweating around the sting site. Therefore, should the ant escape unnoticed, sting site sweating is diagnostic for a harvester ant sting.

  A third difference between harvester ant stings and other stings is localized piloerection, the standing up of the hairs around the sting site. The hairs immediately around the sting puncture stand up much like the hairs on the shoulders of a frightened dog. In addition, “goose flesh” in the area caused by the contraction of single-celled erector muscles at the base of each hair produce a dimpling appearance of the skin. As with sweating, the hairs outside the sting area are of normal appearance. No other insect sting causes localized hairs to stand up; this feature is, again, diagnostic for a harvester ant sting.

  A fourth difference between harvester ant stings and those of other insects is the generation of lymph node pain. The nearest lymph nodes—the axial in the armpit region for stings to arms or the inguinal in the groin area for stings to the legs—become tender and hard. The pain is not sharp or unbearable but is decidedly and noticeably unpleasant. The feeling is hard to describe. I call it “unaesthetic” because it interferes with one’s sense of happiness and well-being. No other insect sting causes lymph node pain or awareness and is diagnostic for a harvester ant sting.

  The fifth difference between harvester ant stings and those of all but one other stinging insect is the length and nature of the pain. Once the pain kicks into high gear in about 5 minutes or so, it continues unabated for hours. It comes in a wave with intense, excruciating, teeth-gritting pain and then recedes to a more manageable level before returning to a new peak, and so on. Unfortunately, the pain does not go away quickly. For most people, it lasts 4 to 12 hours, depending on the species of harvester ant, the amount of venom the ant managed to inject, and the sensitivity of the individual to pain. The pain of rough, red, or western harvester ant stings lasts about 4 hours, whereas the pain of Maricopa, California, or Florida harvester ant stings lasts closer to 8 hours. And I chose to focus my research on Maricopa and Florida harvester ants!

  From the unusual nature of harvester ant sting reactions, I suspected the chemical composition of harvester ant venom must be different from other insect venoms. At the point in the 1970s of my first stings, knowledge of harvester ant venom chemistry was a blank page. The first insect venom chemically characterized was from the horse ant, or English red wood ant, Formica rufa. In 1670, 90 years before Linnaeus gave the ant its scientific name, John Wray determined these ants contained formic acid.31 The acid lacked a name and, subsequent to its discovery in ants, was called “formic acid” after the Latin formica, meaning ant. Wray’s discovery was quite the topic of discussion in scientific circles. Even the public was aware of it. Thereafter, the public and many scientists came to believe that (all) insect venoms were formic acid, a belief that sticks today. Urban myths, such as this formic acid myth, are nearly impossible to dispel. German scientists, starting in the late nineteenth century and into the 1930s, essentially showed that honey bee venom contained highly active solid toxins, unlike the liquid volatile formic acid, and never mentioned an odor of formic acid, something that would be conspicuously obvious if it were present. Likewise, no venomous ants that have functional stingers (formic acid–producing ants lack functional stingers and can only bite) have ever released a formic acid odor when collected or aspirated into a jar. The myth of formic acid in insect venoms is likely to remain part of our street knowledge and to entertain us for decades.

  Because nothing beyond descriptions of sting pain was known about harvester ant venom, my first task was to collect venom for chemical and pharmacological analysis. The ants themselves are easy to collect, but they have only a tiny amount of venom. Each ant produces about 25 micrograms of venom. For an ounce of venom, over 1 million ants would be required, and at 3 minutes per ant, that would require six and a half years of working nonstop, day and night, to collect. Obviously, collecting large quantities of venom was out of the picture. Fortunately, many analyses require only tiny amounts of venom. Enzymes that cleave chemical bonds, thereby cre
ating biochemical havoc within organisms and their body tissues, are one of the effective ways venoms operate. Florida harvester ant venom is a cornucopia of enzymes with more different highly active enzymes than any other insect venom. These enzymes do various things once injected through the stinger into the skin of something like my foot. Two phospholipases, A1 and B, break phospholipids in cell membranes, in the process releasing the fatty, pain-inducing lipid lysolecithin and other fragments, and destroying the cell membrane. Ouch. Another enzyme, hyaluronidase, acts as meat tenderizer to soften the connective tissue in the skin, thereby facilitating entry of other venom components so they can wreak their havoc. Other enzymes, including esterase and acid phosphatase, break down other molecules in the skin and body, thereby synergizing the activity of other venom components. Whether these are outright toxic on their own is unknown. One last enzyme is particularly intriguing. It is lipase, an enzyme that breaks bonds in fat molecules.32,33 The exact function of lipase, an enzyme unknown from any other venom, remains a mystery, but my suspicion is that it, perhaps with esterase, causes a sharp, rashy feeling like that produced by stinging nettle plants.

  Active direct pharmacological and toxic actions are another hallmark of harvester ant venom.34 The venom is highly hemolytic, rapidly destroying the membranes of red blood cells. Destroyed blood cells release their hemoglobin with the combined effect of impairing oxygen transport in the body and clogging the kidneys’ filtering system. Without functional kidneys, one dies a painful death over several days. Hemolysis can be an indirect cause of death.

  Kinins are highly active peptides most famous for affecting cardiac activity, lowering blood pressure, and causing pain. Wasp kinins appear to be the main cause of the pain from yellowjacket and other social wasp stings. Kinin-like activity is pharmacologically detected in harvester ant venom, although the exact chemical structure of the molecule that produces the kinin-like activity has not been determined.35 The effect of this activity in a sting reaction is unclear, likely causing short-term pain.

  Harvester ant venom’s most profound activity is its direct neurotoxicity. This neurotoxicity directly targets nerves in the skin, spinal cord, brain, and, likely, the heart. Near instant death can be the result. Small vertebrate predators are at serious risk from even a few harvester ant stings. Fortunately, for people, the amount of venom in a few stings is too low to have a meaningful toxic effect. In addition, our thicker skin is a marvelous slow-release system for venom. The venom from a few stings gets stuck in the skin and is only released at rates below that which would do systemic damage.

  Venom lethal toxicity is measured as the median venom dose required to kill half of the victims. In contrast to snake venoms where lethality values were well known, the only insect venom for which we had a value was the honey bee. Honey bee venom is remarkably toxic, surpassing the toxicity of many snake venoms. To our surprise, when harvester ant venoms were analyzed, their potencies dwarfed that of honey bees. The venom of an average species of harvester ant is 6 times more deadly than honey bee venom, and the Maricopa harvester ant from Willcox, Arizona, is about 20 times as toxic.36 To date, harvester ant venom is the most toxic known insect venom, more toxic, even, than all snakes, except for a handful of Australian and sea snakes. If harvester ants were the same size as sea snakes, I suspect we would know a lot more about their venom.

  In their quest to defend the colony, some harvester ant species have another trick in their magician’s toolbox. A major limitation of many insect sting systems is the speed of venom delivery. Ants and bees lack forceful mechanisms for near instantaneous venom delivery. A major benefit of rapid venom delivery is getting a large quantity of venom into an assailant before being discovered and removed or killed. Harvester ants in the California species group and in the Florida ant have a marvelous system to get around this venom-delivery problem. They simply autotomize their stings into the flesh of their target. In so doing, the ant can be removed, squashed, eaten, or what have you, yet the autotomized and intact venom system remains and continues unobtrusively delivering its full payload of venom. Sting autotomy is familiar in honey bees and is considered diagnostic for bee stings: If a stinger is left in the skin, it is a honey bee. If a stinger were not present, then it is something else. This wisdom is only partially true; harvester ants and several, mostly tropical, species of wasps also leave their stings embedded in the flesh. The individual ant dies, but its full venom delivery helps protect the colony superorganism, including queen, immatures, and other adults. Because worker harvester ants are reproductively sterile, the suicidal ant sacrifices no direct reproduction, and her strategy of total venom delivery maximizes the chances that her close kin, the queen, brothers, reproductive sisters, and colony they live in, have an enhanced probability of reproducing.

  This brings us to the sting of harvester ants. Harvester ant stings are definitely not for the faint of heart, making the beekeeper’s task appear like a stroll through the meadow. Harvester ant stings are serious, bad, and painful. They might start out innocently at first, perhaps feeling a bit like someone is injecting tiny amounts of water through a dentist’s syringe into the tender spot, but the sensation soon morphs into a sharp, digging pain. The pain is sometimes like the dull, heavy thud of being hit with a lead-filled blackjack; other times like a wizard is reaching deep below the skin and ripping muscles, tendons, and nerves. Except the muscles, tendons, and nerves are not ripped only once but in waves: ripping now, easing a bit, ripping again. To make the point even clearer, the torture continues unabated for several hours. Expect 4 to 8 hours of pain. On the pain scale, harvester ant stings command the very high level of 3, substantially higher and worse than that of a honey bee sting. These stings beg for stories to loved ones and friends as gestures of care and compassion.

  9

  TARANTULA HAWKS AND SOLITARY WASPS

  I would rather be stung a hundred times by digger wasps

  than once by that darling of the philosophers, the honeybee!

  —Howard Evans, Wasp Farm, 1973

  ELECTRIC. A BOLT OUT OF THE HEAVENS. That is what tarantula hawk stings feel like. The question is not are tarantula hawk stings different from those of other stinging insects, but why and how they are different. “Why” questions present a problem for science, as they suggest some purposeful reason behind the observation, and purposes are not amenable to scientific methods. For the moment, if we ignore that limitation and view the “why” as a catalyst for liberating our minds to generate ideas that explain our observations, then we open the door to understanding. Ideas that flow through the door can then be tested and, with good fortune, lead to understanding.

  A good start to searching for the whys of tarantula hawk sting pain is in the biology of tarantula hawks and other “solitary” wasps. Solitary in the sense of wasp biology means lack of sociality, that is, not living in colonies with sisters, brothers, mothers, and growing young. Instead, solitary wasps live a life of the single female who must do everything herself so that her offspring survive and carry on her lineage. Solitary wasps are true single moms. Male wasps do no work whatsoever to assist in producing the next generation. Males only mate with females to provide the necessary sperm; otherwise, they are mostly a nuisance to females in their continuing, amorous courting. In some bees, males actually provide some benefit by guarding the nest entrance and by blocking it with their head to prevent intrusion by parasites or other usurping female bees. These males truly are using their heads. Unlike bees, no solitary wasps share a common nest with other females, and males do not use their heads to protect the fort.

  Solitary wasps are generally predators that actively hunt and overpower prey. Bees, however, are vegetarians, sipping nectar or other sweet liquids and munching on pollen from flowers. One peculiar group of bees, the Scaptotrigona, commonly called “vulture bees,” abandoned pollen collecting in preference to scavenging meat from dead animals. These bees are the exception to the vegetarian bee rule. Solitary wasps have their own
exceptions to their predation rule. The exceptions are the pollen wasps in the subfamily Masarinae, relatives of the potter wasps, named for their often exquisite pottery vases in which the young are reared. Pollen wasps, as the name suggests, collect pollen to provide for their young instead of prey. They are an example of convergent evolution with bees, as they are not closely related to bees, residing on a different branch of the evolutionary tree of life.

  If you are a wasp, solitariness has several disadvantages compared to sociality. No, we are not referring to social life in the sense of human social life—friends, parties, shopping together, shared meals, mutual laughs. We are referring to lacking the advantages of siblings and the community effort to enhance life’s prospects. Social insects have multiple individuals to work on a task and can usually do the job better than any one individual. For example, one member might find a food bonanza, such as a large, dead grasshopper or a new patch of flowers. The individual can only harvest a small portion of the resource alone and might lose all of it to competitors. A social individual can recruit others to dominate and harvest the large resource. A member of a solitary species that fails to find food or water can be in dire straits. If a member of a social species fails in foraging, usually others succeed and can share the take with the individual that failed. Solitary individuals must be jills-of-all-trades and do everything themselves. In social species, individuals can specialize: some collect food, others collect water, some collect resources for nest building, others feed and care for the young, and still others defend the nest. This partial list is only an illustration of potential specializations and is far from complete.1 One important advantage of sociality is the ability to have someone always at the nest to defend it from predators, parasites, or intruders. Solitary wasps must leave the nest to secure food, prey, and water, leaving the house open with nobody to guard the baby.

 

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