The Sting of the Wild

by Justin O. Schmidt

  If Dick Bohart could pick up velvet ants, why not me? After all, they are fast and even little ones are difficult to suck into aspirators, a sandy operation requiring time and much sand spitting. Large velvet ants are even more difficult to catch. These speedy fur balls will not fit into aspirators, are nearly impossible to catch with forceps, and when scooped into a jar or large vial are often accompanied by large quantities of sand and debris, something that requires removal later. Maybe Bohart had a point. So I began casually, the term being used loosely, picking them up and putting them in empty, cleaned peanut butter jars. Actually, the operation was more like holding the jar a few inches from the zigzagging, fleeing velvet ant, frantically pinching sand and velvet ant and raising the combo slightly higher than the jar before throwing it in the direction of the open jar mouth. Usually, this worked, and I merrily continued catching more. But one day while trying to get a striking black and orange Dasymutilla klugii, she nailed me. Although the sting was superficial, penetrating the skin for at most a few milliseconds, it produced an immediate sharp, rashy pain that once again produced this overwhelming urge to rub the site. The pain was mostly gone in 2–3 minutes, and entirely gone in 10 minutes, but the rashy feeling returned for days afterward when touched. Pain rating of 2 on the scale. Two months later, and not having learned my lesson, I was picking up an attractive glorious velvet ant, Dasymutilla gloriosa, a species clad in very long, fluffy white hair, and got the same thumb hit again. Sharp, intense, deep pain, again without causing redness or swelling, and the familiar rashy feeling and urge to rub ensued. Pain level also 2, but this time, by 6 hours a clearly defined area on my thumb had swelled into a tight pocket reminiscent of the medical term “compartment syndrome.” This well-delineated tight area remained for three days and then receded. Out of sight, out of mind. Then, exactly two weeks later, all the skin in that area of tight swelling peeled off. Sometimes with stings strange, inexplicable reactions occur. This was one such reaction; was it an immunologically mediated Arthus reaction rather than a normal reaction? Who knows?

  10

  BULLET ANTS

  I can only liken the pain to that of a hundred

  thousand nettle stings. —Richard Spruce, Notes of a Botanist

  on the Amazon and Andes, 1908

  When I picked her [a Paraponera] up, she stung me and

  immediately it felt like someone had smashed my thumb

  with a hammer. —Marlin Rice, 2014

  BALA, TUCANDÉRA, CONGA, chacha, cumanagata, munuri, siámña, yolosa, viente cuatro hora hormiga, bullet ant. These are some of the common names for Paraponera clavata, the world’s most painfully stinging bee, wasp, or ant. This impressive giant ant, with its stocky, black body and impressive jaws and stings, is known and given a local name by people wherever it occurs. But don’t let this ant’s primitive appearance deceive you into thinking it is just a slow, dim-witted brute. It is a lithe, arboreal acrobat, all too ready to demonstrate its agility as it clings and stings. Paraponera knows no fakery, it’s the real thing. Paraponera is the insect star in stories worthy of telling to one’s grandchildren and in the 2015 movie Ant-Man. If stung, you might not think you will live to see grandchildren, but, rest assured, no one has ever died from bullet ant stings.

  The bullet ant, Paraponera, inhabits moist forests stretching along the Atlantic Ocean side of the continental divide, from Nicaragua in Central America to Brazil in South America. On my first visit to the Costa Rican tropical research station at La Selva, I was greeted by a conspicuous sign warning to be exceedingly cautious of the stinging bullet ants. This struck me as odd, given that the station nestled in a rainforest was home to dangerous and potentially lethal fer-de-lance snakes. No signs were planted in the grassy areas around the station about fer-de-lances. My quest at the station was to study the marvelous bullet ants and their defenses and venoms. As an entomologist, I had a healthy respect and admiration for these ants and immediately set out to find them. Because bullet ants are active both day and night, I headed out at night equipped with headlamp, jars, and the usual insect net. An army ant column had been seen crossing the path earlier, so I made a side trip off to find their bivouac. Going through the undergrowth was tough. About five minutes in, I heard this “flop, flop,” emanating from somewhere in the leaves in front of me. At first, nothing was visibly causing the sound. Then I saw it. A huge 2-meter-long fer-de-lance was rearing its head off the forest floor and flopping down into the dry leaves, hence the flopping sound. While elevated, the snake’s mouth was open. Fair enough, the snake was warning me in two ways not to step on it. Without the warnings, the snake was perfectly camouflaged and invisible among the leaves. After admiring it and taking some pictures, I decided the only safe way to proceed was to put the snake in my insect net (a fine herpetological tool) and hold it at arm’s length in front of me. That way, I would always know where it was and couldn’t step on it. It was heavy. A 10-pound snake held 6 feet away quickly becomes a tiresome challenge. The snake interaction caused me to lose track of my course, and the army ants were nowhere in sight. Unless I wanted to spend the night alone and lost in the forest with a big snake, it was time for plan B: the snake was unceremoniously tossed downhill, and I headed uphill to the path. That was it for the night. I asked the local herpetological expert at the station about the fer-de-lance. He asked, “Does it have keels [central ridges on each scale] on its scales?” “Are you kidding? Get that close to see keels?” He figured it was not a fer-de-lance at all, as they have no keels, rather a bushmaster. Bushmasters are the largest venomous snakes in the New World, attaining a length up to 3.5 meters, and are the most deadly Costa Rican snake. At that time, six of the seven recorded bitten people had died. He surmised I had run into a “small” bushmaster. Sure enough, when the film was processed, the scales had keels. And the station warns about bullet ants!

  Bullet ants, though not lethal, are impressive. They left indelible images in the minds of early naturalists and their readers. One of the earliest writers was the botanist Richard Spruce, who wrote of his experience on August 15, 1853, in Amazonas:

  Yesterday I had the pleasure for the first time of experiencing the sting of the large black ant called tucandéra in Lingoa Geral. … I did not notice that a string of angry tucandéras poured out of the opening I had made. I was speedily made aware of it by a prick in the thigh, which I supposed to be caused by a snake, until springing up I saw that my feet and legs were being covered by the dreaded tucandéra. There was nothing but flight for it … but not before I had been dreadfully stung about the feet. … I was in agonies, and had much to do to keep from throwing myself on the ground and rolling about as I had seen the Indians do when suffering from the stings of this ant. … I can only liken the pain to that of a hundred thousand nettle stings. My feet and sometimes my hands trembled as though I had the palsy, and for some time the perspiration ran down my face from the pain. With difficulty I repressed some inclination to vomit. … After the pain had become more bearable [3 hours], it returned at 9 o’clock and at midnight, when I stepped out of my hammock on my left foot, and each time caused me a hour of acute suffering. … It is curious that nothing was visible externally more than would be caused by the sting of an ordinary nettle. … I came worse out of this encounter than any other in which I have been engaged since entering South America. Many times have I been stung by ants and wasps, but never so badly.1

  Spruce was not alone in noticing the sting of bullet ants, so named because victims sometimes likened the pain to being hit by a bullet. Algot Lange wrote in 1915 of his trip on the Javary River tributary of the Amazon River during which he was stung on his leg by a bullet ant: “The pain almost drove me out of my senses for fully twenty-four hours, and the inflammation abated only the third day after the bite [sic]. When the Brazilians declare that four tucandeiras will kill a man I believe it; while perhaps he will not die from the actual poisoning, he might from the agony associated with such bites [sic].”2 Hamilton Rice, a medic
al doctor, writing a year earlier of his explorations on the northwest Amazon, offered these observations: “The insects and pests of these regions make existence a continual torment and seriously interfere with the power of work. The worst and most dreaded of the ants is the tucandéra or conga, the bite [sic] of which causes the most excruciating agony lasting for several hours, sometimes attended by vomiting and hyperexia [hyperthermia].”3 Apparently, bullet ants made a greater impact on people than the diseases of yellow fever, malaria, or river blindness.

  Nearly four decades after Rice, Harry Allard, a Washington, DC, botanist, writes of attempting to pick up Paraponera (misidentified as Dinoponera, an even larger ant) using several folds of a handkerchief. He describes the ant as “a handsome shining black insect an inch or more in length and fears no one” and continues describing the sting to the end of his index finger: “the pain was soon excruciating and lasted until well into the night. So severe was the pain that at times my hand trembled. The next day there were redness and swelling, but no other local symptoms.” Some weeks later he was stung twice on the ankle “and in a short time I was in the throes of an agony of burning pain—a pain such as I have never experienced before, nor ever care to repeat. … I could not keep my foot quiet for any length of time.” Allard goes on to describe a sting to his 3-year-old grandson who “with a child’s curiosity” had picked one up, the pet dog’s sting to a paw, and the mortal fear of two white-faced monkeys.4 Fast-forward 60-some years to Terry Erwin, the Smithsonian Institution biologist who invented canopy fogging to survey insect biodiversity in tropical forests and has spent more time in bullet ant territory than anyone I know: “I’ve seen snakes and all that kind of stuff and been stung by Paraponera. It’s a real shock when you get stung and you know immediately [his emphasis] what it was. … So I grabbed that thing and pulled it out. … I was just squeezing and squeezing, and then it dropped out, but they are so hard I didn’t kill it and it was crawling away. That lasted about half an hour, and by day two, oh, then after the fire, it goes to feeling like a dull toothache and the toothache kind of goes for a couple of days.”5 Enough belaboring the point, I think we can appreciate that bullet ants are no ordinary ants.

  What makes these ants so unusual? An adventure into ant taxonomy and bullet ant natural history provides clues. The 15,000 or so described ant species currently fall into 16 subfamilies. Until recently, only 9 subfamilies were commonly recognized, including the Ponerinae, the third-largest subfamily. This subfamily was a miscellaneous trash can of species, lumped together largely based on their heavy body design, simple colony structure, with simple behaviors, and other “primitive” traits. Paraponera was lumped in this subfamily, albeit a somewhat unusual species given its nasty sting, but otherwise was “just another ponerine ant.” Hence, its behavior and venom were compared to those of other ponerine ants. Why, then, was it so different? In the past decade, genetic analyses of ants have revealed that Paraponera was not in the subfamily Ponerinae after all. And its previously presumed closest sister group, the genus Ectatomma, was taxonomically even more distant, more closely related to the formic acid–spraying carpenter ants of one’s backyard than to the ponerines. What this taxonomic diversion tells us is that the bullet ant, now in its own subfamily of one species, is truly a unique ant whose lineage separated from other ants around a hundred million years ago.6 Thus, Paraponera should not be expected to be especially similar to other ants, no matter how similar these other ants might superficially look, or whatever their taxonomy.

  The biology of bullet ants differs from that of other ants. They live mainly in nests in the ground near the base of trees. Although their nests are in the ground, they do not forage on the ground around the nest entrance, preferring to climb up the trees into the forest canopy to forage. Sometimes they will climb into the canopy, only to return down a different tree or some of the abundant vine-like lianas to the surface, where they forage at distances as great as 60 meters from their nest entrance. This foraging behavior seems to be a way to prevent leaving a trail or other clues for potential assailants or competitors to locate the colony. Sometimes colonies will be located aboveground in the forest trees; these nests are usually located in sizable quantities of debris and humic material that has a consistency similar to soil that accumulate in the crotches of large trees. In Costa Rica, newly mated queens tend to locate their colonies near one particular species of tree, Pentaclethra macroloba, apparently based on chemical odor.7,8 This nesting behavior apparently reflects local conditions, as they are opportunistic and flexible ants. This nesting flexibility was apparent on Barro Colorado Island in neighboring Panama, where colonies were associated with 76 species of trees, shrubs, palms, and lianas, none of which were Pentaclethra, a species not present at the site.9

  Bullet ants are no velociraptors of the ant world; they are mainly vegetarians, consuming sugary solutions of sap, fruit juices, and other unknown sources present in the forest canopy. Unfortunately, sugars do not provide the protein necessary for growth of bullet ant larvae or egg production by the queen. To meet these protein needs, bullet ants also become predators of an assortment of insects, spiders, and other invertebrates. Even hard, spiny, biting leaf cutter ants—those big-headed orange ants seen in nature programs moving in long columns, carrying green leaf flags as they march home—are taken.10 Foragers, typically larger individuals from among a continuous worker size range of about 15 to 22 millimeters, are, nevertheless, choosy in what prey they will accept. Many chemically protected caterpillars or other noxious prey, including the strawberry (colored, not tasting!) poison-dart frog, Oophaga pumilio, are rejected. The poison-dart frog is rejected not because it is a frog but because of its taste; similar-sized, cryptically colored frogs in the genus Eleutherodactylus are accepted.11

  Bullet ants, though large, are not primitive or the dumb brutes of the ant world. They live in large colonies of up to 2,500 individuals and are as capable as honey bees in learning timing of food rewards and exhibit learning based on experience and orientation cues.12 When a rich source of food is located, bullet ants can recruit nestmates to the source via a chemical trail pheromone they lay down by rubbing their abdomen on the surface as they return.7,13,14 They can even evaluate the benefits and costs of recruitment based on the concentration of sugar solution and the travel distance.15

  As idyllic as bullet ant life appears, all is not always well. Like our own species, their worst enemies might be themselves. Sometimes huge fights between colonies erupt with a dozen or so enemy pairs engaged in often mortal combat.16 Intercolony conflict results in overdispersed nests in the environment, that is, not randomly dispersed as in the BB holes in a shotgun target. Instead, they more uniformly separated from one another. Colonies closer together than 20 meters have significantly higher mortality rates than those farther apart. Mean colony life expectancy is only 2.5 years, with intercolony aggression a major factor contributing to the short life expectancy.17

  Other than neighboring colonies, bullet ants have few natural predators. I have observed that other ants, even army ants, do not seem to bother them. The one record of vertebrate predation on bullet ants that I could find was reported in 1943 by Albert Barden. Barden inventoried the stomach contents of a large number of basilisk lizards, not the huge basilisk snake of Harry Potter fame, but midsized lizards commonly known in Central America as Jesus Christ lizards for their ability to run on water. Among the 1,141 separate food items found in basilisks were a few bullet ants.18 Whether these were active foragers or were injured combatants fallen from trees, we will never know. In any case, vertebrate predation in nature of bullet ants is rare at best.

  MEET THE TOAD PROJECT. While I and two colleagues were in the Guanacaste dry forest of Costa Rica, we took a break from studying “killer” honey bees (Africanized bees) and ventured over the mountain spine to the Atlantic rainforest. There, some bullet ant workers were collected and brought back to Guanacaste. Around the dinner table at La Pacifica where we were staying
was an abundance of giant cane toads, Bufo marinus. Toads are among the most indiscriminate predators and are deterred by very little. If it moves, it is eaten. Hugh Cott reported his tests on the palatability of honey bees to common English toads, Bufo bufo, in 1936. He determined that toads readily eat the first presented bee and some learn after one or more stings that bees are a bit too spicy for them. Other toads repetitively ate bees despite receiving up to five stings before avoiding more bees. His study showed that toads are hardy, readily endure stinging punishments, and are sometimes slow learners, but eventually within seven days all learned that bees are not preferred food.19 Given that toads seemed to be the toughest predators around, and were readily available around our table, we decided to test the palatability of bullet ants to them. We chose a random, good-sized toad and tossed it a bullet ant. Down the hatch went the ant. The toad responded by “hiccupping” body jerks, eyes bulging in and out, and mouth gaping. Apparently, the toad was stung. Would the toad learn? No. Down the hatch went the second bullet ant. Same toad reaction. Did it learn after two ants? No. Down went a third, with the same reaction. The toad ate nine bullet ants in a row, each time reacting to the stings. At this point, we had run out of bullet ants, so we tossed a nonstinging insect to the toad to see whether the reaction would be the same as for a bullet ant. Down it went without a hint of discomfort. Toads are tough, and apparently might possibly be predators of bullet ants, though something not reported from the field. This table-side test shows how extreme a predator must be to tackle a bullet ant.

  Perhaps the greatest impediments to the life of bullet ants are not predators but tiny parasitoid flies. As mosquitoes torment human lives, flies, Apocephalus paraponerae, torment bullet ants. These flies are roughly the size of common vinegar flies that love our overripe bananas and are cherished in genetic research labs. Unlike vinegar flies, they deposit their eggs on injured bullet ants. When one of these flies hovers near a bullet ant nest entrance, in the words of one writer, “more than 10 ants came rapidly out of the nest and went berserk trying to catch it.”20 Within minutes after an injured ant is presented, flies come from seemingly nowhere to the ant. Both male and female flies arrive. Females oviposit on the ant, the maggots consume the ant, and up to 20 flies result.21 We asked, How do the flies locate the injured ants so quickly? A promising lead came from the odor released by injured ants. Bullet ants contain in their mandibular glands a ketone, 4-methyl-3-heptanone, and its corresponding alcohol. An injured ant releases these odors. To test the possibility that these chemicals were attractants, we added them to highly refined olive oil to make a system for slow chemical release. Sure enough, flies were attracted to the baits.22 That these flies have a highly specific and effective means of discovering and exploiting their food source indicates injured ants are not scarce and that battles between individual bullet ants are a major source of mortality.