Killing machine

Portia, one of nature's most versatile predators

It takes the lead in the often macabre predator-prey dance with breathtaking cunning and relentless efficiency and will do whatever it takes to see the union end in grisly death, seldom its own.

It is one of nature's most efficient serial killers, and it is no larger than a button on a man's dress shirt.

It is Portia, a member of the Salticidae or jumping spider family, a creature that for 10 years has been the focus of research by R. Stimson Wilcox, a Binghamton biology professor, and his collaborator, New Zealand biologist Robert Jackson.

The genus Portia contains 15 species of African, Asian and Australian spiders, none exactly local denizens. Still, despite its diminutive size and the remoteness of its habitats from Binghamton, Wilcox has spent thousands of hours in the lab and in the field stalking, studying, recording and writing about these "smart" little spiders and their amazing abilities.

What Wilcox is discovering is that when it comes to the morbid traits of the predator, Portia isn't just a jack of all trades; it is the mastera tiny killer with a bag of deadly tricks that rival predators hundreds of times its size and apparent evolutionary complexity.

Portia is known to use its legs, palps, body movements or various combinations to make vibrations mimicking everything from a trapped insect to an interested suitor on the web of its intended victim. These signals lure the prey spider closer to its fateful demise, giving rise to the label "aggressive mimicry" for Portia's predatory behavior.

Like all jumping spiders, Portia has eight eyes. A large pair up front demonstrates excellent visual acuity and the ability to see color. Three smaller, less obvious pairs, aligned in rows from front to back along the top of its head, appear only to sense light and motion, Wilcox said.

All those eyes come in handy, however, because Portia, like other salticids, stalks its prey visually.

"If you see a spider and it whips around and looks at you with two big eyes, it's a jumping spider," Wilcox said. Several species of jumping spiders are indigenous to the Southern Tier, he added.

Unlike some of its colorful jumping cousins, Portia is cryptically colored or camouflaged and looks a lot like a small piece of bark or dried up vegetation. All the better to eat you, if you happen to be amongst its favorite prey.

"Portia is among the most formidable invertebrate predators and almost certainly is the most formidable arthro pod," Wilcox said.

Even when stacked up against sharks, creatures whose predatory reputation is legendary, Portia appears to be far more intelligent, Wilcox said.

"When we talk about 'intelligence' with Portia, we're talking about genetically based ability," Wilcox notes. "It's all built in. The versatility of these animals, with their tiny neural systems, is almost unbelievable."

Portia, in fact, is very much like a jungle cat in its stalking abilities and style, he said.

In contrast to most other spiders, Portia prefers eating spiders over other insects. That often means risking its own life and limb with forays into other spiders' webs, but Portia has developed an impressive array of behaviors to increase its success at conducting such raids. Individual Portia spiders occasionally fall prey to their intended victim, but such miscues are the exception to the rule, Wilcox said. Even if bitten by other spiders, Portia demonstrates a high tolerance for or immunity to most prey-spider venoms.

Among the myriad ruses employed by the cunning Portia is the selective use of environmental smokescreens. In other words, when the opportunity presents itself, Portia uses wind, dropping leaves, or the presence of any environ mental "noise," including movements by other animals to disguise its own stalking motions on the web of a prey spider. Given the presence of an environmental smokescreen, the stalking Portia moves farther and more quickly on a prey spider's web than in still conditions, Wilcox said.

The use of environmental smokescreens is not uncommon in predator-prey interactions, but Portia is the first arthropod described as using this strategy.

Even more exciting, however, is the compelling evidence that Portia is capable of initiating its own smokescreen signals, Wilcox said, a behavior never before reported in any predator.

Portia also seems able to mimic such environmental "noises" as a leaf or raindrop to simultaneously mask its presence and forward motion on the web.

For Portia, trial-and-error learning is part of what appears to be a dynamic feedback system between predator and prey.

"Portia is so versatile in ferreting out in trial-and-error fashion what works to kill another spider that we've never put Portia up against any web-spinning spider that Portia hasn't been able to kill, whether that spider was one Portia had ever before been associated with in nature or not," he said.

Wilcox and Jackson also have evidence of Portia's limited ability to "think," that is, to assess a problem, plan a strategy to solve that problem and carry out its plan. In field and laboratory experiments, Portia has demon strated an incredible ability to "figure out" how best to sneak up on prey.

Even when to do so demands that the spider create a three-dimensional cognitive map of where it plans to go and maintain that map for an hour or more, Portia has proven itself capable of "detour behavior"the ability to successfully execute, with a high degree of flexibility, pathways that require it to lose sight of and at times even travel away from its prey in order to improve its chances for a kill.

When Portia intends to dine on such non-threatening prey as insects or spider egg sacks, however, it doesn't waste its energy on stalking, signaling or smokescreen behavior, demonstrating an intriguing variation that again seems to involve something akin to reasoning: No threat, no guile.

To be "eaten" by Portia, by the way, could make being chewed up and devoured by some other predator seem almost civil. When Portia pounces on its victim, sometimes after hours of almost imperceptible stalking, it injects a broad-spectrum venom capable of killing virtually any arthropod. It then injects into the subdued prey its own digestive juices, perceptibly deflating its own abdomen in the process.

After a few minutes, Portia then sucks the juices back out of the prey animal and continues this process cyclically until the prey animal has been completely "digested," leaving behind a fragile, hollowed out exoskel eton as the only evidence of the kill.

Portia, in fact, is such a formidable predator that, in a sort of "evolutionary arms race," some prey spiders have actually "learned" through natural selection to recognize its walk on their web, Wilcox said.

When Portia's presence is sensed, these particular prey spiders panic and abandon their weba drastic response no other spiders tested could provoke in them. The response is aptly termed " Portia panic" by Wilcox and Jackson.

A November 1996 National Geographic article on their work titled " Portia: Mistress of Deception," underscored Jackson's and Wilcox's reputation as the world's foremost Portia experts.

Among the topics discussed in the article was the "ingenious" system Wilcox has devised to record the full range of web vibrations in Portia's repertoire, as well as a variation on that system that allows the researchers to turn the tables on Portia with some mimicry of their own.

Wilcox's recording system involves placing a voltmeter pointer on a web, in a sort of mechanical version of the linesperson's hand on the net cord in tennis. When the spider moves, the web vibrates the pointer, triggering an electrical signal that is recorded on tape, eventually to be digitized for computer analysis.

By attaching a tiny, one millimeter-sided magnet to Portia's head and placing an electrical coil above the spider, Wilcox is also able to play back the computer-generated signals, which vibrates the magnet, simulating Portia's signaling on the web.

In this way, Wilcox can explore in even greater detail how it is that Portia uses its cloak of vibratory disguises and smokescreen "non-messages" to control the behavior of the prey spider.

His is basic research, Wilcox said, and though he is fond of telling his students, "There is no substitute for the real thing," he knows that some people disagree. Some would just as soon step on every spider they see and don't appreciate the worth of his work.

"What most of these people don't understand is that we have only scratched the surface. The majority of fundamental biological insights that have ultimately helped people came from this kind of basic research."