web and spider in the forest in the sunlight on a summer day, the background forest

Weekend Reads | Spider Brains: How Tiny Creatures Create Large Cognitive Systems

by Kevin Schofield

For this weekend’s read, we’re going to explore an idea at the intersection of biology and philosophy. It’s a paper written in 2017 by two biology researchers, one in the U.K. and the other in Brazil, that challenges our preconceived ideas about cognition and how we draw the boundary around the portion of our bodies that allows us to think.

The researchers begin by offering up a helpful definition of “cognition”: the acquisition, processing, storage, and use of information. That’s casting a pretty wide net: It includes perception, interpretation, memory, decision-making, and response. They then note that among the ongoing debates within the field of cognitive science is whether cognition happens just within an animal’s central nervous system, i.e., the brain and the network of nerves distributed throughout the body, or whether cognition happens in other parts of the body as well. They go on to suggest an even broader third option: that animals can incorporate things outside of their bodies into their cognitive systems. Do they, in effect, offload some of their thinking to other things in their world?

This could, in fact, be a very important survival trait. If one’s environment is complex and challenging, then having a large brain can be a crucial advantage if it allows one to adapt to survive and to prey upon other creatures that are themselves adapting to survive. But a brain that’s big enough to deal with the complexities of a changing environment, or to manage the social relationships that come with living in a large group, comes at a cost: It takes up a lot of space, it’s heavy, and, most of all, it takes a lot of energy to keep it going. For large mammals, it’s a good trade-off; the brain, as a proportion of the overall body and its energy consumption, is a manageable investment. But for small creatures — like spiders — the investment is probably not a good one. 

But in an interesting twist, the researchers argue there’s more to the story here than simply concluding that small creatures will rarely if ever develop large, complex nervous systems capable of advanced cognition. Instead, they suggest this would encourage them to adapt to use their environment as an extension of their own cognitive systems, such that they get cognitive benefits without the biological cost.

Their prime example is spiders’ use of silk webs to catch their prey. It’s well-known that spiders will sit on their webs and wait to sense the vibration of prey getting caught to know when and where to pounce. But more recent research has shown that there is far more to spiders’ use of their webs. They can differentiate between a wide variety of vibrations, sensing, for example, whether their potential meal is a small or large insect. This is important because it needs to judge whether the meal is worth it: Will it provide enough food to be worth all the energy it takes to subdue it, and what are the risks to the spider’s safety for trying to make it a meal? A tiny fly might not be worth the effort; a large insect might fight back and overpower the spider.

But some spiders’ abilities go even further: They “tune” their web, much like a stringed musical instrument, to control what kind of information they get — and how much. Over time, spiders will tighten and loosen specific threads in the web; tighter threads are more sensitive to vibrations from smaller prey. In this way, they can loosen up the web to ignore tiny insects, or tighten it up if food has been scarce recently and they need all the food they can get. Spiders can also learn which portions of their web are the most productive and will strengthen and tighten those areas to optimize for the greatest return.

Perhaps the researchers are on to something: It certainly sounds like spiders are creating a very complex extension of their nervous system outside of their bodies. The silk threads aren’t just conveying information; they are selectively conveying it based upon their construction and subsequent tuning. The spider is truly offloading some of its own cognition into the web itself.

Even the task of constructing a web seems to be optimized for maintaining a small brain. Spiders need to have some internal model or pattern of the web they are creating, plus the ability to measure distances. But the shapes seem to be designed so spiders don’t need to keep the entire plan in their head: By building it in repetitive pieces, they can reuse the limited amount of neurons they have to just remember just the small portion they are currently working on at any given time.

The researchers point to one further complexity of this system: Other creatures have adapted to use the spiders’ web cognition against them. So-called “jumping spiders,” which prey on their cousin web-spinning spiders, like orb weavers, have learned to mimic the different kinds of vibrations that prey — and potential mates — might cause, so they can sneak up on a spider and catch it unaware.

Why should we care about all this? Because we humans are doing the same thing; in fact, we’re further along the path of extending our cognitive systems outside our bodies. For thousands of years, we have created written artifacts for storing and sharing information, constantly innovating, improving, and building up our knowledge. More recently, we have become very talented at building other kinds of devices that can substantially enhance our other cognitive abilities: cameras (both chemical and digital), the telegraph and telephone, a wide variety of sensors, audio and video systems, and now, of course, advanced “AI” that can process huge quantities of information and draw inferences from them. 

How much practical difference is there between a spider interpreting vibrations on its web and a human with a mobile phone in her pocket she’s set to vibrate mode? We humans are not just using technology to enhance our cognitive abilities; we’re also using it to connect ourselves into our environment and extend our nervous systems. 

To date, human brain implants are fairly crude and still mostly fodder for science fiction. But they are improving rapidly: Soon, they might become mainstream methods of compensating for hearing or vision loss, for controlling prosthetic limbs, or, perhaps one day, for bypassing spinal cord injuries. Further out, though, when body implants can connect to things outside of our bodies — maybe even to other people — how will that change the way we perceive the limits of our own bodies? And if we continue to find evidence that a wide variety of living creatures commonly extend their cognitive systems out into their surrounding environments, will we think it so weird when we start doing the same? Maybe it’s not weird at all; maybe it’s a natural outcome of living in a highly complex world.

Extended spider cognition

Kevin Schofield is a freelance writer and publishes Seattle Paper Trail. Previously he worked for Microsoft, published Seattle City Council Insight, co-hosted the “Seattle News, Views and Brews” podcast, and raised two daughters as a single dad. He serves on the Board of Directors of Woodland Park Zoo, where he also volunteers.

📸 Featured image by Andrei Metelev/Shutterstock.com.

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