Millions of years ago, a few spiders abandoned the kind of round webs that the word “spiderweb” calls to mind and started to focus on a new strategy. Before, they would wait for prey to become ensnared in their webs and then walk out to retrieve it. Then they began building horizontal nets to use as a fishing platform. Now their modern descendants, the cobweb spiders, dangle sticky threads below, wait until insects walk by and get snagged, and reel their unlucky victims in.
In 2008, the researcher Hilton Japyassú prompted 12 species of orb spiders collected from all over Brazil to go through this transition again. He waited until the spiders wove an ordinary web. Then he snipped its threads so that the silk drooped to where crickets wandered below. When a cricket got hooked, not all the orb spiders could fully pull it up, as a cobweb spider does. But some could, and all at least began to reel it in with their two front legs.
Their ability to recapitulate the ancient spiders’ innovation got Japyassú, a biologist at the Federal University of Bahia in Brazil, thinking. When the spider was confronted with a problem to solve that it might not have seen before, how did it figure out what to do? “Where is this information?” he said. “Where is it? Is it in her head, or does this information emerge during the interaction with the altered web?” A spider’s web is at least an adjustable part of its sensory apparatus, and at most an extension of the spider’s cognitive system.
This would make the web a model example of extended cognition, an idea first proposedby the philosophers Andy Clark and David Chalmers in 1998 to apply to human thought. In accounts of extended cognition, processes like checking a grocery list or rearranging Scrabble tiles in a tray are close enough to memory-retrieval or problem-solving tasks that happen entirely inside the brain that proponents argue they are actually part of a single, larger, “extended” mind.
Consider a spider at the center of its web, waiting. Many web-builders are near blind, and they interact with the world almost solely through vibrations. Sitting at the hub of their webs, spiders can pull on radial threads that lead to various outer sections, thereby adjusting how sensitive they are to prey that land in those particular areas. Tensed regions, then, may show where the spider is paying attention. When insects land in tensed areas of the webs of the orb spider Cyclosa octotuberculata, a 2010 study found, the spider is more likely to notice and capture them. And when the experimenters in the same study tightened the threads artificially, it seemed to put the spiders on high alert — they rushed toward prey more quickly. The same sort of effect works in the opposite direction, too. Let the orb spider Octonoba sybotides go hungry, changing its internal state, and it will tighten its radical threads so it can tune in to even small prey hitting the web.
Another example of this sort of interplay between web and spider comes from the web-building process itself. According to decades of research from scientists like Eberhard, a spiderweb is easier to build than it looks. What seems like a baroque process involving thousands of steps actually requires only a short list of rules of thumb that spiders follow at each junction. But these rules can be hacked from inside or out.
When experimenters start cutting out pieces of a web as it’s being built, a spider makes different choices — as if the already-built portions of silk are reminders, chunks of external memory it needs to retrieve so it can keep things evenly spaced, Japyassú said. Similarly, what happens in a web once it is built can change what kind of web the spider builds next time. If one section of the web catches more prey, the spider may enlarge that part in the future.
Extended cognition may partly be an evolutionary response to an outsized challenge. Vollrath at Oxford, believe that webs are more like tools the spider uses. “The web is actually a computer, as it were,” he said. “It processes information and simplifies it.” In this view, webs evolved over time like an extension of the spider’s body and sensory system — not so much its mind. Vollrath’s lab will soon embark on a project to test just how webs help the spiders solve problems from the extended phenotype perspective, he said.
What are you thinking now homo sapien reader?
Art: Sin Eater for Quanta Magazine