Arachnophobes often cite the unpredictable movement of spiders as the basis of their fear, pointing out how each thin leg appears to lift, bend, and examine with an impending degree of autonomy.
Perhaps disturbingly, research done by me and my colleagues has revealed that each of a spider’s bones does indeed enjoy a certain independence of the brain – especially in the complex task of web building.
Our study showed that spider bones have ” their own minds ”, which construct webs without supervision over the spider’s brain. This has important implications for the field of robotics, which may draw inspiration from this example of decentralized intelligence to build similar autonomous robot limbs.
To reach our conclusions, we observed the common garden spider Araneus diadematus, a creature we all know – both in the backyard and as the heroine on the pages of the children’s book Charlotte’s Web.
Web Engineers
Spiders serve many functions. They provide a safe home, but it is also an invisible and very dynamic trap set up to catch and then trap any insect that strays too close.
To perform this function, webs use a strong, structural scaffold with radiating spokes with ‘catch’ spiral ‘built on top, which is soft and sticky and uses an extremely clever microscopic rolling mechanism to remove a spider’s prey.
The trapping coil not only uses electrostatic charges to catch a fly, it contains a complex glue to hold it firmly and a specific elasticity that makes the web stretchable for the leg of an unfortunate insect to repel in his struggle for freedom.
The analogy of the internet as a ‘web’ is good: because at least five different sys are used in a cobweb, the way they cross and network with each other creates a kind of information filtering capability – with small vibrations noticed at always by a spider’s listening bones.
Spider diagram
Given the incredible complexity of spiders, we have to ask how such a small animal – with an obvious brain – can design and build this advanced structure. Modern technology has helped us to begin to understand how spiders handle such a complex task.
By filming and tracing the movements of its eight legs, we were able to locate a spider’s web building in intimate detail and reveal the construction process as a kind of dance around a central pivot, with a precise choreography of repeatable rules.
These rules are surprisingly simple. Each step and wire manipulation follows a fixed action pattern, with one of the spider’s legs measuring an angle and a distance to place it and then connecting one wire to each other with a quick glue – always with impeccable accuracy 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 series of thousands of small steps and actions, each building on the previous steps and actions. This iterative process invests the network with ’emerging properties’ – special features that manifest due to different components working together – which in turn offers excellent architectural and engineering functionality.
Outsourcing
It seems that the complexity of the task (or rather foot) in building a web requires spider brains to outsource the work on the eight legs. Put another way, spider bones build webs semi-autonomously – eight phantom limbs performing their dance in local, closed feedback loops.
We discovered this after studying spiders that built sites within frames in our laboratory. In some experiments, we cut the threads of a web being built. In others, we have twisted the web like a giant wheel. This research was not done to irritate the spider: it was to help us determine the rules that apply to web building.
With a set of rules in place – including rules that help spiders build a disrupted web – we taught them to Theseus, our virtual spider.
The new rules we learned Theseus – based on the dances of real spiders we observed in our lab – revealed that each leg is actually an independent agent to set up a lot of web building. This in turn helped us solve the mystery of how spiders build perfect webs after losing a bone.
If a spider is caught, it is discarded and a shorter leg is regenerated the next time the spider braids its exoskeleton. This substitute is not only half the size of a normal leg, it is also a different shape with different hairs and sensors. Yet spiders with regenerated legs somehow build perfect webs.
Author provided
Evolution has allowed cobwebs to think for themselves in a sense, which means that the different properties of regenerated legs do not affect the construction of a web.
It relieves the brain from managing eight legs that perform complex activities, freeing it to concentrate on survival actions such as herding predators. This efficient, decentralized system is remarkably relevant to modern robotics – often inspired by the natural world in their artificial design.
Read more: Why do robots look like animals and humans?
Spiders are not alone in decentralizing tasks of the brain – most animals do so to some extent, such as the constant beating of a human heart. But with their webs, spiders offer us a concrete, observable, and enchanting way to measure and understand how this decentralization works.
This neat trick lies in the incorporation of a spider of simple task calculations within the structure of its limbs. Robotics call it morphological computers, and have only recently discovered its operation relatively recently. The humble garden spider, it seems, has been using it for over 100 million years.