Stung by a tarantula hawk? The advice I give in speaking engagements is to lie down and scream. The pain is so debilitating and excruciating that the victim is at risk of further injury by tripping in a hole or over an object in the path and then falling onto a cactus or into a barbed-wire fence. Such is the sting pain that almost nobody can maintain normal coordination or cognitive control to prevent accidental injury. Screaming is satisfying and helps reduce attention to the pain of the sting. Few, if any, people would be stung willingly by a tarantula hawk. I know of no examples of such bravery in the name of knowledge, for the reputation of spider wasps — specifically tarantula hawks — is well known within the biological community. All stings experienced occurred during a collector’s enthusiasm in obtaining specimens and typically resulted in the stung person uttering an expletive, tossing the insect net into the air, and screaming. The pain is instantaneous, electrifying, excruciating, and totally debilitating.
Howard Evans, the great naturalist and author of the classic book “Life on a Little Known Planet,” was an expert on solitary wasps. Howard, a slight, reserved man with a shock of white hair and a sparkle in his eyes, was especially fond of tarantula hawks. Once, in his dedication to the investigation of these wasps, Howard netted perhaps 10 female tarantula hawks from a flower. He enthusiastically reached into the insect net to retrieve them and, undeterred after the first sting, continued, receiving several more stings, until the pain was so great he lost all of them and crawled into a ditch and just sobbed. Later, he remarked that he was too greedy.
I know of only two people who were “voluntarily” stung by tarantula hawks. I say “voluntarily” as both were performing their duties as part of documentary films, which, among other things, “encouraged” being stung. One was a young, handsome athletic entomologist who knew of the wasps. He deftly reached into the large cylindrical battery jar and grabbed a wasp by the wings. He had her in such a position that her sting harmlessly slid off his thumbnail. We prattled for a minute or so about tarantula hawks while the camera scanned close up to the long sting as it slid harmlessly, missing its mark. Then with a great heave the wasp pulled its abdomen back and thrust the sting under the nail. Yeee…ow (I can’t recall if any expressions unsuitable for general audiences were uttered), the wasp was hurled into the air and flew off unharmed. One point for wasp, zero for human.
The other was a solidly built fellow who was apparently a master of performing pain-defying acts of bravery. For the film, I was charged with catching the wasp and delivering it to the scene. Five or six tarantula hawks were easily netted from flowers of an acacia tree; unfortunately, the net snagged on some thorns, and all but one wasp escaped. The remaining wasp appeared to be a male, so I summoned the cameraman to demonstrate how males cannot sting and are harmless. I reached in and casually grabbed “him.” At this point, I realized that I was holding a “her.” Yeee…ow, except this time it was me. I managed to toss her back in the net, while attempting to explain my blunder and pain on camera. As I was not in the film – perhaps fortunately – the footage was relegated to some obscure studio archive, perhaps someday to be resurrected on YouTube. That episode over, the tarantula hawk was delivered to the rightful actor. He grabbed her, was stung, and showed no reaction beyond a begrudging “Ouch, that did hurt a bit.” I figured the guy had no nerves. But his director then handed him a habanero pepper, a tarantula hawk of chili peppers, which he enthusiastically bit into. He became instantly speechless, convinced fire was blasting from his mouth, nose, and ears. Apparently, he did have some nerves — sensitive at least to chili peppers.
How could such a small animal as a tarantula hawk be so memorable? Several years ago I attempted to address this question in a paper entitled “Venom and the Good Life in Tarantula Hawks: How to Eat, Not Be Eaten, and Live Long.” The natural history of tarantula hawks provides some insights. Tarantula hawks are the largest members of the spider wasp family Pompilidae, a family some 5,000-species strong that prey solely on spiders. The feature of tarantula hawks that makes them so special is their choice of the largest of all spiders, the fierce and intimidating tarantulas, as their target prey. The old saying “you are what you eat” rings true for tarantula hawks: if you eat the largest spiders, you become the largest spider wasps. As with other spider wasps, the female wasp provides each young with only one spider that serves as breakfast, lunch, and dinner for its entire growing life.
The law of supply and demand applies: large spiders produce large wasps; small spiders produce small wasps. The story doesn’t end here. Momma wasp is not entirely at the whim of fate and fortune in the size of spiders she encounters. She has the special ability to choose the sex of her babies. Hymenoptera (the order of insects consisting of sawflies, wasps, bees, and ants) are oddballs in the genetic world: females are produced from fertilized eggs, and males are produced from unfertilized eggs. This not only means males have half the genetic information of females; it also means mom can choose to produce a son or a daughter by selectively allowing stored sperm to fertilize the egg. In the tarantula hawk world, females are valuable. They do all the work, take all the risks of capturing the spiders, and have to drag a spider sometimes eight times their weight to their burrow. Thus, females need to be big and strong to do the job efficiently and to produce the most young. Males mainly sip nectar from flowers, chase other males, and mate with females. A small male can mate with a female, so size is not so crucial, though a bigger male is usually more successful in winning more females. Mother tarantula hawks choose to give the valuable resources of large tarantulas to female young and small tarantulas to male young.
Tarantula hawk life history is similar to that of many other solitary wasps. Female adults emerge from their underground cells to seek nectar for food and to mate. Males emerge to seek flowers and to begin mating behavior. Male tarantula hawks in the genus Hemipepsis are famous for their hilltopping behavior. They go to hilltops, ridge lines, or other prominent high points and establish leks, or mating territories. In these territorial leks, males battle other males to defend their territories, with larger males usually winning the best territories, often near the center of the lek. Virgin females visit the lek to seek mates. They mate briefly once in their lifetime and get on with life. Mated females then embark on finding tarantulas. They tend not to be fussy and take tarantulas of several species, both male and female tarantulas and adults and large immatures. Large, plump, juicy female tarantulas are mostly destined to become food for baby female tarantula hawks. Scrawny, long-legged male tarantulas are mostly destined as food for the next-generation male tarantula hawks; hence male tarantula hawks are often tiny compared with their sisters.
Tarantula hawks sting their tarantula prey between a leg base and the sternum, the plate between all the legs. The sting, directed at the large nerve ganglion that controls the legs and fangs, inactivates and permanently paralyzes the spider within one-and-a half to two-and-a-half seconds. The now limp spider is dragged to a nest burrow, constructed by the female wasp, or to the tarantula’s own nest burrow. Anyone fortunate to witness at dusk the unfolding of one of nature’s great dramas, as a tarantula hawk drags her enormous spider long distances over the ground, is treated to an adventure remembered for a lifetime.
The spider is placed in a cell at the bottom of the nest tunnel, an egg is laid on the spider, and the tunnel is filled with dirt and sealed. The mother’s duties now done, she is off for another prey. The egg hatches in a few days into a first instar larva that imbibes blood from the live, paralyzed spider. Over the next 20 to 25 days, the larva grows, molting its skin four times, and finally becomes a fifth instar larva. The spider is still alive at this point, even though the larva has eaten blood, muscle, fat, digestive system, and reproductive system, leaving the heart and nervous system. The fifth instar now rapidly consumes the rest of the spider before it can spoil. With the food exhausted, the larva spins a silken cocoon and pupates. In early season, the pupal stage may be only several weeks, after which the adult emerges. Later in the season, the wasp overwinters in the cocoon phase to emerge the next spring. Adult males live a few weeks or so, whereas females can live four to five months.
One of the great mysteries is why tarantulas do not fight back when a tarantula hawk attacks. Why a huge spider, whose powerful fangs easily crush an enormous cockroach or a hard beetle, fails to defend itself against a wasp is unfathomable to the human mind. How can the tarantula passively submit to its killer usually without the tiniest defense? We cannot journey into the mind of a spider to answer this question. This question also pertains to the spider prey of most, if not all, of the thousands of other spider wasp family members. Perhaps escape and freezing is a better defense in the long run than fighting. How the tarantula distinguishes a tarantula hawk from a cockroach or beetle is also not known, although some ideas seem reasonable.
Unlike humans who “see” the world through our eyes and, secondarily, through our ears, with touch, taste, and smell minor modalities, spiders, insects, and most other invertebrate animals sense the world primarily through smell and secondarily with touch and some vision or hearing. In spiders and insects, smell includes contact receptors on antennae, pedipalps [appendages on the front of a spider’s head], legs, and other body parts. Many of these receptors detect surface chemicals on their prey. The surface chemical blends provide a signature of their source that the insect or spider can recognize. To us, a wasp smells pretty much the same as a beetle, a moth, or a fly — that is, it has no odor — but to a spider or an insect, they are distinct. The tarantula, a nearly blind animal, likely recognizes the tarantula hawk primarily by its odor, perhaps aided by the wasp’s “feel” and the vibrations it sends through the soil surface or air pressure waves. The wasp might also be recognized by the distinct airborne odor it releases. This distinctive odor is easily detected by humans, especially when the wasp is captured or threatened. The odor is pungent, not harsh, but somehow repellant.
Naturalists frequently commented on the odor. Alexander Petrunkevitch, an eminent early arachnologist at Yale University, noted one tarantula hawk, when contacting the jaws of a tarantula, “raised her wings and suddenly produced a rather pungent odor,” which he concluded “the production of this odor must be a sign of anger, perhaps of warning.” F. X. Williams, the man who probably studied tarantula hawk behavior more than any other person, described the odor as “the Pepsis odor,” a familiar and universal odor among Pepsis species. Howard Evans noted that both males and females of Pepsis “have this characteristic odor, and this odor may well be repellant to predators.” Sadly, although we know the odor is produced in the mandibular glands, so named because they are at the base of the mandibles, we have not identified its chemical nature.
This is not from lack of trying. I have worked with five or six excellent chemists over more than three decades, and we have failed to solve this mystery. Also mysterious is the role, or roles, of the odor. The most evident role is chemical defense against predators, including entomologists, that try to catch them. This defense is not direct, as with carpenter ants that spray corrosive formic acid on assailants or blister beetles (the group containing “Spanish fly”) that cause painful, vesicating skin rashes; rather, it appears indirect in the form of an odorous warning to stay away. (The honesty of this warning defense is obvious to anyone who has grabbed a female tarantula hawk.) The odor also might be an aggregation pheromone that attracts both males and females to rich floral sources, to resting places to congregate, or to lekking areas for mating. Finally, the odor might serve to flush a tarantula from its burrow and/ or prevent the spider’s natural defensive behavior. As often occurs in biology, the odor might have first evolved for one role and later been selected for several additional roles.
Let’s return to the question of why the tarantula does not fight back. Could it be that the wasp somehow inactivates the spider’s defenses or frightens it with its motion, wing buzzing, or odor that the spider is paralyzed with fear? Such a concept surely seems too wildeyed to be real, but who knows. We have little understanding of fear and how it changes behavior. One thing we do know is that the battle is highly lopsided in favor of the wasp. Even when the tarantula does fight back, its fangs are mostly useless, simply sliding off the wasp. Tarantula hawk bodies are hard, smooth, and slippery, have no rough areas, indentations, or ridges, and have rounded bodies. The tarantula has the same problem with its sharp fangs that a person would have attempting to hold a glass beer bottle in one hand while drilling through its side with an electric drill in the other hand: the fangs and drill bit simply slide off sideways. Several observers have reported that, when tarantulas actually attempt to bite and crush a tarantula hawk, loud snapping sounds can be heard as the fangs under immense force abruptly and repeatedly slip off the wasp’s body. In the end, the wasp emerges unharmed. Perhaps, rather than fighting, the best spider strategy may be to run and then freeze in hopes the wasp loses interest. I am glad our own species rarely encounters similar situations.
We humans are masters of our lives. We no longer fear large animals that may prey on us, having long since dispatched most of them and their threat. We have conquered many human diseases, though more continue to emerge to challenge us. We have tamed animals and manipulated plants to provide a steady, more reliable food supply. We have made clothes and shelters to make life comfortable. We have made games and toys to entertain ourselves. Tarantula hawks have not mastered their lives as well as humans, although they are a close second.
Of course, by “mastered” I do not suggest that tarantula hawks made conscious decisions to alter their lives as humans have (we have no evidence of consciousness in tarantula hawks); rather, nature, through natural selection, has made them masters of their lives. Tarantula hawks live long lives, they have no known predators of adult females, and they can be active any time of day and anyplace they choose. How was this good life achieved? Defense against predators is the most important factor in a long and free life. Without good defenses, animals must either live secretive and restrictive lives or have short lives and try to mate and reproduce before being eaten. No predators successfully prey on healthy female tarantula hawks, although I did once see a particularly small male wasp being eaten by a large praying mantis on a milkweed flower.
Pinau Merlin, an Arizona naturalist, reported coming upon a roadrunner — that intrepid predator of many life forms, including rattlesnakes — stealing a paralyzed tarantula from a tarantula hawk and then feeding it to her young. The wasp was left alone. The obvious reason large predators such as roadrunners, other birds, lizards, toads, and mammals don’t prey on tarantula hawks is their sting. The sting alone would not be sufficient to protect the wasp from being smashed and eaten by a powerful bird beak or crushing lizard jaws. Here, the second defense, the same defense that protects against the tarantula — the hard, slippery, rounded body shell — provides the necessary time to deliver the sting. The wasp is too tough to be smashed fast enough by beaks and jaws to avoid a sting to the mouth or tongue, and mammalian teeth slip off the wasp body long enough to allow the sting to be engaged. The enormous body size of tarantula hawks relative to most insects and arachnids provides defense against arthropods. If size alone does not do the trick, the sting, hard-body integument, and powerful sharp jaws complete the defense against arthropods.
A universal law of life is that it is always better to avoid a fight with a predator than to actually fight the predator. The key to avoiding an attack is communication to the attacker that an attack is risky. Tarantula hawks are masters of this kind of aposematic communication, using many forms of warning signaling. Brilliant conspicuous color patterns of reds, yellows, oranges, or whites combined with black are classic examples of warning coloration. Strikingly shiny, reflective, or iridescent dark colors are another example. These patterns tell the predator “see me, I am bright, bold, and dangerous; if you attack me you will suffer.” Tarantula hawks with their strikingly reflective orange or shiny black wings and iridescent gunmetal blue-black or black bodies send the warning strongly.
To supplement the visual color pattern, tarantula hawks engage in a distinctive jerky movement while they are on the ground, and they flick their wings while moving around, an action that ensures they are seen. Threatened tarantula hawks communicate acoustic warning sounds by buzzing their wings, much as threatened bees raise their buzzing to a high pitch. A final tarantula hawk warning signal is its powerful odor. Humans, as a species with poor olfactory abilities, only notice the odor when massive amounts are released by a threatened wasp. Small amounts of the odor likely are continuously released and operate as a long-distance, early-warning signal to olfactorily-cued mammals, warning them not to approach. Given all these warning modalities, no potential predator is left unaware of a tarantula hawk.
Imagine for a moment what freedom from predators means. With no predators, there is less hurry in finding a mate and reproducing; no predator-based reason to have a short, efficient life; no reason to avoid open areas, flowers, or ground surfaces, where predators might take notice; and no reason to limit activity periods to times when risks from predators are minimal. For a tarantula hawk, such freedoms are essential. Tarantulas are not abundant, they are hard to find, they are widely dispersed in the environment, and they are available throughout much of the year. Tarantula hawks require much time and searching for both their own food and for tarantulas for their young. They could not easily pass on their genes to the next generation without a long life and few restrictions on their activities.
The sting has been accepted as an amazing given. Just what makes the sting so powerful? What is the chemistry that makes it so magical? Tarantula hawk venom damage to predators is trivial; at best, the lethality to mammals is only about three percent of that of honeybee venom. Why is tarantula hawk venom nontoxic and nonlethal? Perhaps because natural selection operated against a venom chemistry that is toxic or lethal to tarantulas. A venom toxic to mammals might well also be toxic to tarantulas. Dead tarantulas yield dead tarantula hawk larvae. In addition, tarantula hawks defend no nest and have little reason to damage or kill a predator: the goal is to get the predator to cease and desist, and to open its mouth quickly, allowing the wasp to escape. Only a momentary mouth opening is needed for the wasp to fly away, and the pain alone does that marvelously.
The chemistry responsible for tarantula hawk sting pain is not known.. Whatever the various active components of tarantula hawk venom, both humans and tarantulas survive a sting; an important difference between the two is that the tarantula succumbs to the tarantula hawk larva, and we – very fortunately – do not.
Justin O. Schmidt is a biologist at Southwestern Biological Institute and is associated with the Department of Entomology at the University of Arizona. He is the coeditor of “Insect Defenses: Adaptive Mechanisms and Strategies of Prey and Predators.”