Do you think that spiders are mindless machines, driven by pure instinct to make their webs and then attack intruders? Well, it’s time you met Portia:
In an emerald rainforest of northeastern Australia, a sunbeam pierces the canopy, touches broad green leaves on the way down, and beams onto a lichen-spotted rock surface. In the beam’s circle, the slow, careful motions of a brownish jumping spider are illuminated. The jumping spider belongs to the genus Portia and it is stalking its prey, a different species of spider sitting in its own web. Portia steps cautiously from the rock surface out onto the web and stops. Delicately, Portia begins to pluck the web with its palps and legs, making signals that mimic the struggles of a trapped insect. When the prey spider ignores Portia’s plucking, Portia varies the characteristics of the signals, generating a kaleidoscopic of what appears to be a random selection of signals. Eventually, in response to one of these signals, the prey spider swivels toward Portia. Immediately, Portia backtracks to that particular signal and repeats it again and again. There being no further response from the prey, Portia eventually reverts to broadcasting a kaleidoscope of signals. When the prey spider still moves no farther, Portia adopts another ploy.
Now Portia slowly and carefully stalks across the web toward the resident spider, intermittently making a variety of signals. From time to time, a soft breeze blows, ruffling the web. The ruffling creates background noise in the web, and Portia exploits these moments, during which the resident spider’s ability to detect an intruder is impaired, by stalking faster and farther during these periods than when the air is still. Nearing the resident spider, Portia makes a signal that elicits from the resident spider a sudden, rapid approach. However, the spider advances very aggressively, and Portia scrambles to the edge of the web, then turns around to look over the scene. Soon Portia moves away from the web and undertakes a lengthy detour, first going away from the prey and around a large projection on the rock surface, losing sight of the prey spider along the way.
About an hour later, Portia appears again, but now is positioned above the web on a small overhanging portion of the rock. After anchoring itself to the rock with a silk dragline, Portia next slowly lowers itself down through the air, not touching the web at all. Arriving level with the resident spider, Portia suddenly swings in, grabs hold of the unsuspecting spider, and sinks its poison-injecting fangs into the hapless victim.
I’m going to leave the light on tonight, too.
This rather dramatic account is from a chapter in The Cognitive Animal written by Stim Wilcox (Department of Biology, SUNY Binghamton) and Robert Jackson (Department of Zoology, University of Canterbury, New Zealand)1.
For those of you who like visuals, here’s a brief video of Portia:
Clearly, you don’t want to mess with Portia.
In their essay, Wilcox and Jackson note how tricky it is to discuss cognition in animals, with almost as many definitions of the term as people using them. Rather than trying to choose a single definition, they instead apply a framework designed to raise questions about six separate cognitive properties: reception (taking in information), attention (focusing on particular tasks), representation (maintaining a mental image or cognitive map), memory (retaining information), problem solving (deriving pathways to the achievement of goals), and communication language (influencing other individuals by manipulating symbols).
They then run through these properties point by point, in the process illustrating the cognitive abilities of Portia.
Reception: In this area, Wilcox and Jackson emphasize Portia’s amazing eyesight, which apparently is more acute in distinguishing spatial features than that of any known animal of comparable size and even rivals that of primates: “Portia can precisely locate and identify spiders from a distance of 30–40 body lengths away, monitor the spider’s orientation and behavior during the course of a predatory sequence, and in general quickly gain critical information for predatory decisions during complex interactions with a dangerous prey.” For an in-depth article on Portia eyesight, you can check out this piece2 by Jackson and Duane Harland (I love the title: “‘Eight-legged cats’ and how they see”).
Attention: Wilcox and Jackson highlight the extraordinary, prolonged attention paid by Portia as she hunts, especially as she singles out and zeros in on a prey spider in an extended bout of stalking that involves multiple tactics and focused flexibility over time. They note how she must be particularly attentive, given the extreme sensitivity of her prey’s own web to movement and weight, and describe how she manipulates the signals she sends across the target’s web (aggressive mimicry) and opportunistically takes advantage of wind-caused background noise and vibration to move more quickly across the web than she does when the air is still (smokescreen tactics).
Representation, Memory, Problem Solving: For these areas, Wilcox and Jackson point to her planned detours, which demonstrate problem-solving and suggest mental maps and prolonged memory. They observe that, by planning ahead and formulating a solution before executing her maneuver, Portia comes particularly close to what we might typically call “thinking.”
Communication: Finally, while acknowledging that Portia clearly does not have any sort of verbal language or use symbols with arbitrarily assigned meanings, Wilcox and Jackson describe the way in which Portia strings together series of signals as she engages in aggressive mimicry, noting how this involves a complex, flexible and dynamic sequence of interactions between her and her target. As they put it, “Studying Portia’s signal-making strategy from this perspective may bring us closer than we initially expected to something like the cognitive implications of verbal language.”
I don’t have much to add here. Hail Portia!
1Wilcox, S. and Jackson, R. (2002). Jumping Spider Tricksters: Deceit, Predation, and Cognition. In M. Bekoff, C. Allen & G. Burghardt (Eds.). The cognitive animal: Empirical and theoretical perspectives on animal cognition. pp. 27–33. Cambridge, MA: MIT Press.
2Harland, D. and Jackson, R. (2000). ‘Eight-legged cats’ and how they see – a review of recent research on jumping spiders (Araneae: Salticidae). Cimbebasia 16: 231–240.