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You’re confronting a spider, up close, womano-a-womano. The tiny creature rears back on its hindmost legs and assumes a threatening posture, ridiculous given that you could easily squash it with your shoe. Yet everyone understands the gesture, even though to locate the most recent common ancestor shared by the two of you, you’d have to go back roughly half a billion years. The basic language of threat is nearly as old as that other basic language, DNA. Threats between living things have long been grist for the evolutionary mill. And human beings aren’t immune.

As I write this, Russia’s Vladimir Putin is threatening to invade Ukraine. He sees Ukraine as a threat to his power and country were it to join NATO. Ukraine, NATO, and the United States are responding with counterthreats. For all we know, the threats are real; certainly, none is ridiculous. The consequences are immense, with war in the balance.

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A threat, as I consider it here, involves an effort at deterrence, communicating that if someone does something that the threatener seeks to prevent, the consequences—typically some form of retaliation—will be sufficiently aversive to prevent the potential perpetrator from perpetrating in the first place. Living things are typically equipped with a range of intimidating options, not just baring teeth and claws, but also displaying horns, antlers, poison fangs, bony shields, uttering scary hisses and formidable roars, puffing body up, flattening ears down, rattling, hissing, spitting, screaming, flapping wings, staring unwaveringly, even sometimes becoming weirdly quiet.

Heavy Armor: Pound for pound—more accurately, gram for gram—the mantis shrimp is among the most heavily armed of all animals.worldclassphoto / Shutterstock
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Things get interesting when threat-purveyors exaggerate their capabilities, leading recipients, on occasion, to call their bluff, which in turn results in the threatener trying to maintain credibility while the target seeks to determine whether the threat is genuine. Most people wouldn’t take a spider’s threat seriously, but it’s a different story for another spider, or a would-be spider predator, who might well be uncertain what to do next. Believe the threat or see through it?

When threatening another animal, standard procedure is for threateners to make themselves seem larger, more dangerous, imposing, stronger, healthier, more experienced, and more motivated than they really are, all in the service of avoiding actual combat while preventing an opponent from taking their food, nest site, mate, or, quite simply from attacking. For the threat to work, the threatener must signal that it has weapons and is willing to use them. Even if neither is true. Talk is cheap, certainly cheaper than fighting, so getting your way via a threat is often a good deal.

It’s fine to speak softly and carry a big stick, but if your stick is small, why not speak loudly anyhow, and hope that will work? Animals no less than people often do just that, bluffing and blustering and threatening to blow the other guy’s house down. One might expect no limit to the aggressive braggadocio out there in the natural world; the payoff to exaggerated threat-making can be great, while the costs appear small.

Bertrand Russell likened the U.S. and the Soviet Union to battling scorpions, which may have been unfair to scorpions.

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But the costs could be high—notably if your bluff is called. When a threat is “honest,” that is, backed up with inclination and ability to meet a push with a shove, there is little payoff to calling a threatener’s bluff. But the more widespread and the more “dishonest” the bluffing, the greater the temptation to question its legitimacy. Honesty, we like to think, is the best policy. Natural born liars, in the biological world, must confront a practical problem that is often shared with their human counterparts: Deceivers run the risk of being tripped up in their dishonesty, especially if their bluff is called. The key is credibility, or rather, the problem of achieving it.

Animals with effective weapons that can intimidate their rivals are not shy about calling attention to their armament, which often carry what biologists call a “reliability component”—characteristics that are impossible to fake—baked into the structure of the weapons themselves. Their threats are likely to be credible and effective.

A small elk or deer cannot successfully pretend to be big. American elk and Scottish red deer rely on their large body size and massive antlers to get their way, especially when it comes to competition between bulls. They frequently engage in “parallel walking,” during which opponents strut their bodily stuff, notably their impressive headgear. When successful, such demonstrations result in the more physically intimidating animal winning without having to fight. Lions have huge canines, not only for killing their prey but also for threatening other lions. They are notably silent when stalking zebras, reserving their impressive roar—along with showing off their magnificent dentition—to discourage other lions from invading their pride. Poisonous snakes with impressive fangs reveal their unique weapons when needed, in the most intimidating way they can. Bighorn sheep call attention to their big horns. If you’ve got it, flaunt it.

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Getting it,” though, is expensive. Whatever the advantages of having strength to flaunt, it is nearly always costly to obtain it. In a 1953 speech, President Dwight Eisenhower noted, “Every gun that is made, every warship launched, every rocket fired signifies, in the final sense, a theft from those who hunger and are not fed, those who are cold and are not clothed. This world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children.” Something similar applies to animals and their “arms.”

Male fiddler crabs have the largest weapons per body size of any animal; fully one-half of a male fiddler’s energy budget is expended in growing their comparatively huge fiddles. Even after they have been produced, these structures impose a resting metabolic rate on their possessors that is 20 percent higher than that of females (which don’t have enlarged claws), simply because of the cost of maintaining so much additional muscle. This doesn’t count the expense of vigorously waving those appendages, as well as added demands when it comes to running with them—especially from predators, something that might well be particularly mandated for male crabs (and to a lesser extent, lobsters), whose oversized claws make their possessors especially desirable prey items because of all that expensive muscle meat inside.

Jolly Roger: For pirates, the payoff for flying the Jolly Roger flag was large because by issuing a credible threat, they increased the likelihood that they could capture booty without having to risk a fight.donfiore / Shutterstock

The costliness of animal armaments—used more often to threaten than to fight—is not limited to invertebrates. The antlers of male caribou can be five feet or more in length and weigh more than 20 pounds; moose, 6.5 feet and 40 pounds. Balanced at the top of the animal’s head and at the end of a long neck, the encumbering weight of these structures is increased by their levering effect. Beyond the stress of walking, running, and displaying them, there is also the cost of growing such devices, estimated at five times the energy requirement of merely keeping the body going. If this isn’t troublesome enough, the demands for calcium and phosphorus to produce massive antlers necessitate that a mature bull elk or moose depletes the mineral content of his bones, resulting in a kind of seasonal osteoporosis, causing brittleness, and rendering males susceptible to life-threatening fractures.

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When it comes to the tension between honest and dishonest threats among animals, the best studied examples come from snapping and mantis shrimp. Pound for pound—more accurately, gram for gram—they are among the most heavily armed of all animals. Their “raptorial appendages” consist of either weaponized clubs that have immense striking power, capable of breaking mollusk shells, or strong and sharp forelimbs used to catch and pierce prey; the former species are sometimes known as “smashers” and the latter, “snappers.” Either weapon type can readily injure or even kill same-species opponents. Not surprisingly, these are conspicuously brandished during aggressive threats.

The largest of these appendages, called “meri,” are part of a male’s armamentarium and are directed toward other males as part of an aggressive signal called a “meral spread.” These displays are especially pronounced and important when competing for a particularly cherished resource: dwelling cavities in rock or coral. Meral spreads by a resident mantis shrimp make the threatening individual less liable to be attacked and increase the probability that an intruder will back off.

However, these crustaceans molt regularly; when they emerge from their discarded carapace their bodies are soft and vulnerable, so they cannot withstand even light blows from opponents. Moreover, in their unprotected state, they are also unable to initiate an effective attack. In fact, the odd times when freshly molted individuals attempt to strike, they injure themselves instead of their opponent. Nonetheless, they display, although because a freshly molted individual cannot effectively back up its display with an actual attack, it’s all bluff.

Talk is cheap, certainly cheaper than fighting, so getting your way via a threat is often a good deal.

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Biologists, notably Roy Caldwell of the University of California, Berkeley, set up a series of clever experiments to test the role of bluff vs honesty among these animals. The researchers gave newly molted and thus vulnerable individuals ownership of highly desired rock cavities in the laboratory. Hard-shelled individuals were then introduced. The well-armored newcomers sought access to the already-occupied cavities. In most cases, the freshly molted residents promptly gave up their real estate, although some first engaged in threat display—they tried bluffing before retreating. The experiment’s control group—cavity owners who were between molts and thus as physically competent as the intruders—had no need to bluff. They responded to trespassers by physically attacking them, with just a few giving a meral display only.

By contrast, among those helpless, newly molted cavity residents who resisted the newcomers, the proportions were almost exactly reversed; a tiny few used a meral threat display and lunged aggressively at the intruders, but then promptly gave up when it was unavailing. Evidently, those that can defend their turf do so. Those that can’t, act as though they can; they threaten. And then leave.

As W.C. Fields is alleged to have recommended, “If at first you don’t succeed, try, try again. If you still don’t succeed, give up. No sense being a damned fool about it.”

In a follow-up study, researchers varied the size of intruders versus resident owners. When they increased the body size of the recently molted (hence vulnerable) residents, the larger individuals were more likely to threaten and less likely to flee. They were able to give the impression of being more intimidating because of body size discrepancy, even though the reality was that they were no more able to back up their threats. In fact, those residents who bluffed were more likely to retain their ownership than those who refrained from displaying.

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In short, if you’ve recently molted, bluffing pays. At least in a laboratory. Among free-living individuals, if a hard-shelled inter-molt enters the cavity of a recently molted animal, the latter is often killed. So, by threatening the intruder, a vulnerable animal is taking a big risk, but also giving itself a chance of winning. In natural populations, roughly 85 percent of cavity residents who give meral spread displays are hard-shelled inter-molts, whose displays are “honest.” This gives the bluffers a chance because intruders who perceive threatening messages would be well advised to believe that they are legitimately backed, not unlike a person who wisely backs away from a rattling rattlesnake.

Stomatopod shrimp aren’t alone in seeking to enhance their credibility when it comes to issuing threats. Among a certain species of recently evolved primate, individuals known as pirates really did display the skull-and-crossbones, an effective way of issuing a threat that was highly credible because pirates were known to be especially violent. Moreover, their credibility was also high because if captured, the consequence—hanging—was severe. As a result, only real pirates dared to fly the Jolly Roger. But the payoff was also large because by issuing a credible threat, pirates increased the likelihood that they could capture booty without having to risk a fight. In June of 1720, there were 22 merchant vessels in the harbor at Trepassey, Newfoundland, when Bartholomew Roberts, a renowned pirate, sailed in with the Jolly Roger flying. The merchant crews all panicked and abandoned their ships. Credibility pays but maintaining it can be challenging. The pirate life is not for everyone. (Nor is encountering those who have chosen that life.)

Military strategy has often involved deterrence, which in turn has struggled with the same problem of credibility as stomatopod shrimp. A distinction is often made in the human case between deterrence by denial—exemplified by the Great Wall of China, intended to persuade would-be invaders that they won’t succeed—and deterrence by the threat of punishment. To be credible, the latter must often be especially vicious. Here is some hair-raising advice from Sir John Fisher, First Sea Lord, Admiral of the Fleet, and widely regarded as the most important British naval figure after Horatio Nelson. It emphasizes that deterrence by punishment is likely to be effective in proportion as the threatener has a fearsome reputation: “If you rub it in both at home and abroad that you … intend to hit your enemy in the belly and kick him when he is down and boil your prisoners in oil (if you take any), and torture his women and children, then people will keep clear of you.”

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Finally, there is the most prominent, current threat, which makes Admiral Fisher’s recommendation seem positively benign: nuclear deterrence. Its liabilities are legion, including that it’s the main justification for the nuclear arms race, is vulnerable to many kinds of failure, and that should nuclear deterrence fail, everything else does. It also struggles with credibility. “One cannot fashion a credible deterrent out of an incredible action,” wrote former defense secretary Robert McNamara. Ironically, attempts to shore up this credibility by making nuclear weapons more usable via “limited nuclear war,” “battlefield nuclear weapons,” “launch on warning,” and “counterforce targeting” have in fact threatened to succeed. In short, by increasing the credibility of the ultimate, omnicidal threat, by making nuclear weapons easier to use, these developments risk the ultimate irony: making it more likely that they will in fact be used.

Bertrand Russell likened the posture of the U.S. and the Soviet Union during the Cold War to two scorpions in a bottle, which may have been unfair to scorpions, who use their stingers to kill prey and to defend against predators, not for mutually assured destruction. Bluffs and counterbluffs, threats and counterthreats—more rarely, actual fights with victories and defeats—all these take place among nonhuman animals. In those cases, the stakes are lower than between Russia and the West over Ukraine. Whether our wisdom is any higher remains to be seen.

David P. Barash is professor of psychology emeritus at the University of Washington. His most recent book is Threats: Intimidation and its Discontents.

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Lead image: Kjetil Kolbjornsrud / Shutterstock

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