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Arachnophobes often cite the unpredictable movement of spiders as the basis of their fear, pointing out how each slender leg seems to lift, flex, and probe with a threatening degree of autonomy.
Perhaps disturbingly, research by my colleagues and I has found that each of a spider’s legs does indeed enjoy some independence from the brain – especially in the complex task of site-building. Web.
Our study showed that spider legs have “their own mind,” building webs without the spider’s brain supervision. This has important implications for the field of robotics, which can draw inspiration from this example of decentralized intelligence to build equally autonomous robot limbs.
To reach our conclusions, we observed the common garden spider Araneus diadematus, a creature familiar to all of us – both hanging in our gardens and as a heroine in the pages of the children’s book Charlotte’s Web.
Web Engineers
Spider webs perform many functions. They provide a safe home, but they are also renowned for being an invisible, highly dynamic trap set up to capture and firmly hold any insects that stray too close.
To fulfill this function, the webs use a strong structural radiant ray scaffolding with what is called a “capture coil” built on top, which is soft and sticky and uses an extremely clever microscopic winding mechanism to attract the prey of a spider.
Not only does the catch coil use electrostatic charges to trap a fly, but it features an intricate glue to hold it firmly and a specific elasticity that makes the web too stretchy for an unfortunate insect’s leg to push it into its struggle. for freedom.
The analogy of the Internet as a “web” is a beautiful one: because at least five different bristles are used in a spider’s web, the way they intersect and connect to each other creates a kind of information filtering ability – with tiny vibrations noted all the time by the listening legs of a spider.
Spider diagram
Given the incredible complexity of cobwebs, we have to wonder how such a small animal – with an obviously tiny brain – can design and build this advanced structure. Modern technology has helped us understand how spiders handle such a complex task.
By filming and following the movements of its eight legs, we were able to follow the construction of a spider web in great detail, revealing the construction process as a kind of dance around a central hub, with choreography precise replicable rules.
These rules are surprisingly simple. Each step and each wire manipulation follows a fixed pattern of action, with one of the spider’s legs measuring an angle and distance in order to place and then connect one wire to the other with a quick bead of glue – always with impeccable precision and spacing. Many years ago, we programmed a virtual spider, named Theseus, to show how it works.
The apparent complexity of the structure is the result of a long sequence of thousands of small steps and actions, each building on the previous steps and actions. This iterative process invests the network with “emergent properties” – special properties that manifest as different components work together – which in turn provide exceptional architectural and engineering functionality.
Outsourcing
The complexity of the task at hand (or rather the footing) of building a web seems to have required spider brains to outsource the eight-legged work. In other words, spider legs semi-autonomously build webs – eight phantom limbs performing their dance in local, closed feedback loops.
We discovered this after studying the spiders that build webs in frames in our lab. In some experiments, we cut the threads of a canvas under construction. In others, we have spun the web like a big wheel. This poll was not done to annoy the spider: it was to help us discern the rules that govern website creation.
With a set of rules established – including rules that help spiders keep building a disturbed website – we taught them to Theseus, our virtual spider.
The new rules we taught Theseus – based on the real spider dances we observed in our lab – revealed that each leg actually does a lot of website building actions as an independent agent. It helped us solve the mystery of how spiders build perfect webs after losing a leg.
When a spider’s leg is trapped, it is thrown away and a shorter leg regenerates the next time the spider molts its exoskeleton. Not only is this replacement half the size of a normal leg, but it’s also a different shape, with different hair and sensors. Yet one way or another, spiders with regenerated legs continue to build perfect webs.
Author provided
Evolution has ensured that spider legs can somehow think for themselves, which means that the different properties of regenerated legs do not affect the construction of a web.
This relieves the brain of micromanaging eight legs performing complicated activities, freeing it to focus on survival actions such as finding predators. This efficient and decentralized system is remarkably relevant to modern roboticists – who are often inspired by the natural world in their man-made designs.
Read more: Why do robots look like animals and humans?
Spiders aren’t the only ones that decentralize brain tasks – indeed, most animals do to some extent, like the continuous beating of a human heart. But with their webs, spiders provide us with a concrete, observable and fascinating way to measure and understand how this decentralization works.
This trick lies in the incorporation by a spider of a simple task calculation into the structure of its members. Roboticists call this calculus morphological and have only relatively recently discovered its power. It turns out that the humble garden spider has been using it for over 100 million years.
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