“Love thy enemy” we are advised. If yellowjackets are our enemy, as our words and actions suggest, should we also not love them? The underlying theme advises that within an enemy is inherent good. What good are yellowjackets, other than providing material for our thrills, excitement, and stories? But, wait, yellowjackets can be fine friends, albeit not fuzzy, touchy friends. Two favorite yellowjacket foods are flies, including biting and disease-carrying flies, and crop-loving caterpillars. Children who live on farms have been entertained watching baldfaced hornets and yellowjackets pounce on barn flies resting on weathered wood. Bryson expressed the enormous toll on flies 150 years ago:
the practical result of destroying all the wasps on Sir T. Brisbane’s estate was, that in two years’ time the place was infested, like Egypt, with a plague of flies. … We do not readily appreciate the indirect benefits which we derive from the labours of wasps, just as we are not perhaps properly grateful to beasts of prey for their equally unsolicited assistance. Cats and weasels, and foxes, though they are not good to eat, are often much more acceptable neighbours to the farmer than rabbits.39
If one were reincarnated as a Paraguayan cow, or the rancher of the cow, another social wasp, Polybia occidentalis, would be a friend, indeed, because they catch prodigious numbers of biting flies, particularly from around the eyes of cows.26
Caterpillars are ecological eating machines, stuffing chewed leaves into their sausage bodies at a seemingly nonstop rate. This might be fine as long as you are not the plant or the plant is not a crop. Polistes wasps feast nearly exclusively on caterpillars, a feature that endears them to some farmers. North Carolina tobacco farmers unwillingly share much of their tobacco leaf crop with tobacco hornworms, enormous caterpillars that relish the nicotine, grow rapidly, molt into fighter jet–shaped hawkmoths, and recently have become the darling laboratory models for insect physiology and neurobiology. These half-ounce caterpillars easily eat a dozen times their weight in juicy, prime tobacco leaves. North Carolina entomologists made little wooden shelters for the wasps, moved them into the vicinity of tobacco fields, brought about substantial reduction in numbers of hornworms, and even prevented economic loss of leaves.40 Tobacco lovers, think twice before harming a paper wasp.
This brings us to the sting of yellowjackets and the baldfaced hornet. These stings are definitely more serious and attention grabbing than those of fire ants. They are bad. On the pain scale, both yellowjacket and baldfaced hornet stings muster the respectable pain level of 2, equal in comparison to the honey bee. Surprisingly, the much larger and scarier baldfaced hornet actually hurts the same or slightly less than a yellowjacket, perhaps indicating that baldfaced hornets are better at the intimidation game. In any event, the stings of either produce instantaneous, hot, burning, complex pain that gets one’s attention no matter what other thoughts were preoccupying the mind. The pain lasts unabated for about 2 minutes, after which it decreases gradually over the next couple of minutes, leaving us with a hot, red, enduring flare to remind us of the event in case our memory should fade. These stings are worthy of storytelling to loved ones.
8
HARVESTER ANTS
Pogonomyrmex californicus is undoubtedly the fiercest,
the boldest and the most irascible ant of the Sonoran Desert.
Furthermore it is the quickest to sting and the effects of the
sting are the most painful. —George C. and Jeanette Wheeler,
Ants of Deep Canyon, 1973
WILLIAM STEEL CREIGHTON wrote in 1950, “There is a persistent belief that in the days when the West was wilder than it is now, Indians would sometimes stake out a human victim across a nest of Pogonomyrmex [harvester ants]. If this was actually done, it would be hard to imagine a more excruciating death.”1 Years earlier, William Morton Wheeler in his classic 1910 book Ants sounded a similar story: “If it be true, as has been reported that the ancient Mexicans tortured or even killed their enemies by binding them to ant-nests, P[ogonomyrmex] barbatus was certainly the species employed in this atrocious practice.”2 Whether these stories have any veracity or are just urban legends is hard to know, though Jeffery Lockwood in his 2009 book Six-Legged Soldiers provides evidence that there might be some truth to the concept of these stories.3 Men of the Northern Miwok in central California voluntarily stood or laid on disturbed harvester ant nests to determine who of the four or five men was strongest. The chief awarded a prize to the man who lasted the longest on the ant mound.4 Ever since literate people met them, harvester ants have attracted immense popular interest and imagination. These ants not only make impressive and conspicuous nests and populate children’s ant farms but also deliver the most painful and unusual stings of any North American stinging insects.
One might be tempted to generalize from experience with stings from honey bees, yellowjackets, baldfaced hornets, various wasps, bumble bees, sweat bees, and even fire ants that all insect stings are sort of like a bee sting, differing mainly in intensity. Anyone who has been stung by a harvester ant knows better. Harvester ants are docile giants of the temperate ant world, unobtrusively going about their business of harvesting seeds for food. They have no attitude like fire ants and cause no harm if left alone. If they are sat on or pinched, however, they deliver a sting that is nothing like a bee sting. The pain is intense, comes in waves, and is deeply visceral. The intense pain lasts 4 to 8 hours, not 4 to 8 minutes, as with a typical honey bee sting.
In addition to Pogonomyrmex, a variety of other ants collect seeds, including Messor, the famed ant of biblical times; Pheidole, the world’s largest genus of ants; Aphaenogaster cockerelli, the long-legged desert ant; and some fire ants. Pogonomyrmex harvester ants, often considered the true harvester ants, are the most conspicuous of the seed-collecting ants in most areas and have captivated my imagination and that of innumerable others. Curiously, of the aforementioned ants, only the harvester and fire ants sting; the rest have nonfunctional stings. Why those other highly successful ants lost their stinging ability is unclear. A leading suggestion argues the loss is a result of competition and predation by other ants, against which the sting is a poor weapon. Fire ants circumvented the problem of an ineffective sting by having an unusual and highly effective venom that when daubed or sprayed on other ants penetrates their waxy protective integumental barrier and kills or disables them.5 Sadly, for the harvester ants, their venom is harmless when topically applied to other ants. Given this venom handicap, these big, slow, methodical, unassuming ants of the American deserts and southeast are doing well. Their name suggests a life of hard work and no play, projecting an image of boredom and a boring life. But boring can be brilliant. Harvester ants have brilliantly carved an enormous niche for themselves in nature and etched indelible images in mankind: images from cartoon depictions of a backyard volcano erupting with angry ants when their home is trespassed, to images of vast stretches of the American West marred with ant castles surrounded by denuded moats of dirt. Grasslands flowing from horizon to horizon, bearing scars of harvester ant mounds, scream images of Earth infected with its version of smallpox. Should we be surprised then that men declared sagebrush wars against entire communities of harvester ants? And compared to the destructive intent of the masters of these wars, can we fault young children, spying big red harvester ants and big black harvester ants, for having the urge to drop a red ant into the entrance of a black ant nest?
As Christmas wrapping paper sales tell of the success of the upcoming Christmas shopping season, insect common names tell of our perceptions of insects. Insect common names are so important that the Entomological Society of America maintains an official registry of insect common names. The organization, some 7,000 insect scientists, has a permanent committee whose sole job is to research, name, and oversee common names—it’s that important. Common names roughly represent human interest in a given insect species and range from the obscure sugarbeet root aphid and the chicken dung fly to the common honey bee. In the battle for the most common names among
ants, the prize goes to the harvester ants, which eked out victory over the second-place fire ants by having six named species compared with five for fire ants. Both groups trounced the bigheaded ant, the sole represented member of the largest genus among all ants. The number of named harvester ant species suggests that people have a driving interest in them. Even the notorious yellowjackets in the genus Vespula only managed four common names. Harvester ants have more common named species than any other genus of stinging insects, bumble bees with their whopping 36 common names (apparently, Americans have a love affair with bumble bees). The common name filter yields such pleasant harvester ant names as the California, the Florida, the Maricopa, the red, the rough, and the western harvester ant.
In contrast, the original taxonomists, dealing directly with the ants, frequently chose more powerful names, often celebrating native American Indian tribes, including the Apaches, Comanches, Maricopas, and Pimas, or scientific names, including desertorum, bigbendensis, huachucanus, and anzensis (referring to the Anza Borrego Desert of California), signifying the harsh environments some species inhabit. Some names were simply poor choices, as exemplified by Pogonomyrmex bicolor, a reference to the red anterior and black posterior of the ants originally discovered and described. When on a trip to Los Ojitos, Mexico, my wife and I found ants of this species that were essentially entirely reddish. So much for names based on color! Finally, the scientific name of perhaps the most celebrated harvester ant, Pogonomyrmex barbatus, translates as “the bearded beardy ant.” No wonder its common name is the “red harvester ant.”
Harvester ants are ant icons of the New World. The 60-odd species span from the western three provinces of Canada through the United States, Mexico, and Guatemala, skipping the rest of Central America, and picking up in South America, where they are present in every country (excepting the small northern countries of Suriname and French Guiana) to southern parts of Argentina and Chile. They have even crossed the Caribbean Sea to Hispaniola. Some harvester ants sport bright-red coats, some various shades of brown or yellow, and others black. Most are large, often 8 mm long (⅓ inch), with the largest reaching 13 mm. The life cycle of all starts the same, beginning with virgin females and males. They usually fly in a mass exodus from their maternal colonies and form mating swarms in which both sexes engage in brief, frenzied mating orgies. Multiple mating by both males and females is the general rule though exceptions occur, and, in some species, mating might occur at, or within, the colony.
An unusual grouping of harvester ants, residing in an area of the sparsely populated American West near the border between Arizona and New Mexico, take the battle of the sexes to a new high. The participants in this mating ritual are a mixture of males and females of the rough harvester ants (Pogonomyrmex rugosus) and the red harvester ant. For their mating system to operate, females of each species must mate within a brief couple of hours with males of both their own species and males of the other species. If a female mates only with one type of male, her future is bleak. If she mates only with her own species, she can produce only reproductives, and, with no worker force, the incipient colony withers and dies. If she mates only with males of the other species, she can produce only workers and not queens. This limits her reproductive ability to producing only sexual males, a booby prize obtained by laying unfertilized eggs that turn into males. The queen’s interest is to mate mainly with males from the other species and only one or two males of her own species. This way she has ample sperm from the other species’ males to produce plenty of essential workers and some sperm from her own males to produce new females. The male’s interest is dramatically different. If he mates with females of the other species, his sperm are wasted on nonreproductive workers, and his genetic lineage dies from lack of production of a new generation of females that carry his genes. If the male mates with females of his own species, he successfully produces daughters to carry on his lineage. Thus, conflicting battle lines are drawn between males and females: females wish to mate with lots of males of the other species; males wish to mate only with females of their own species. One problem occurs. In the short time of the frenzied mating swarm, males and females either cannot, or do not, discriminate between members of their own or the other sex. Once they are engaged in the actual mating act they can distinguish. What’s a male, or a female, to do now while engaged in this blissful act? If a female is mating with her own male, she terminates mating more quickly than if she is mating with the male of the other species. If the male is mating with his own female, he jacks up the speed of sperm transfer relative to the transfer of sperm to a female of the other species. The net outcome of this battle of the sexes is a wash—each partially gets what she or he wants—perhaps a good thing for both, given the alternative of a collapse in their colony population if either succeeds completely.6
The newly mated females, now queens, quickly get on with the business of attempting to survive and found a colony. Meanwhile, the males might remain around the mating arena for a day or two before dying. New queens, as in most ant species, have the fascinating behavior of breaking off their own wings soon after mating and beginning their new life. Males do not, and cannot, break off their wings. Queen wings are structured slightly differently from males and have preweakened areas near their base that allow the wing to snap when bent downward just the right way by the queen. Imagine the engineering necessary to allow queens to flap their wings vigorously enough to carry them upward through the air without breaking, and yet to be easily broken when the queen desires.
The wingless new queens face the most crucial and dangerous time of their lives. They need to find a new nest site quickly and to dig a tunnel to construct a protective chamber at the bottom—all before becoming a meal for someone else or becoming toast in the hot sun. In most cases, each queen ant is on her own in this task. The California harvester ant is an exception. Here, several queens often combine their efforts to make a new nest that they share together. This odd multiple-queen founding by California harvester ants is apparently an adaptation to the exceedingly harsh environment and competition faced by these queens.7 Once the nest tunnel and chamber are completed, the queen seals the tunnel and begins the claustral colony phase in which she raises the first generation of her family. She does this by laying a few eggs and feeding her newly hatched tiny larvae from her own body reserves. Before flying on her mating flight, the queen gluttonously feasts, storing large quantities of energy-rich fat, often more than 40 percent of her total dry body weight.7 Remember the wings she used to have? Those wings were powered by massive thoracic muscles—muscles no longer needed by a flightless queen. Between the breakdown protein from the wing muscles and the fat and protein stored in her body, the queen manages to rear 10 to 12 tiny workers. During this time, she never leaves the protective chamber she built. The one exception is, again, the California harvester ant. One hapless queen is forced to leave the nest to forage for food for the growing larvae.
Once the tiny minim workers emerge and their bodies harden, they take over colony duties from the queen, except egg laying and some pheromone production. The minims open the sealed nest tunnel to the outside and begin foraging for food. They also enlarge the nest, by digging downward and adding new chambers for the queen, brood, and stored food. This first generation of minims is short lived but, assuming all goes well, manages to raise the second generation of now full-sized ants. At the end of the first year, the colony is small, consisting of relatively few workers and the queen. During the second and third years, the colony grows rapidly, both in population size and in nest size. Usually, about the fourth year, the colony is mature and begins rearing males and females to continue the life cycle.8
Ask elementary school children to name the longest-lived animals and typical answers are “turtles” and “sharks.” Ask them about the longest-lived insects, and knowledgeable children will likely say, “queen termites.” Human interest in longevity begins early. Kids and entomologists are naturally interested in long-liv
ed insects, including ants.
What are the longest-lived ants? Harvester ants currently appear to win the award, outlasting all other ants, including the second-longest-lived ants, the honeypot ants, desert dwellers that store honey for lean times in grape-sized individuals who form living larders within the colony. Some harvester ant colonies have been in the same location for decades and are rather obvious. The longevity of a harvester ant colony has been exasperatingly difficult to pin down. Answers are all over the place, from an average of 15 years or 17 years for a colony reared in the lab, to 22 to 43 years and even up to 29 to 58 years.9
The Sting of the Wild Page 12