The movements of the spiders are tracked by scientists as they weave their webs


Researchers at Johns Hopkins University have discovered precisely how spiders build webs using night vision and artificial intelligence to track and record every movement of the eight legs as the spiders work in the dark.

Ovid’s Metamorphosis speaks of the orb weavers, who are said to be the descendants of Arachne, a figure from Greek mythology who wove beautiful tapestries and dared to challenge Athena to a weaving competition. Angry that she couldn’t find any fault in Arachne’s work – and also because the tapestry portrayed the gods in an unflattering light – Athena beat the girl with a shuttle. When Arachne hanged herself in remorse, Athena took pity and turned the rope into a web and Arachne into a spider.

It’s a fitting literary allusion to a new study of how spiders weave their webs, which is no doubt why scientists at Johns Hopkins University referred to Ovid’s story in a recent article published in the journal Current Biology. The JHU team used night vision and AI to record every movement of several hacked orb weavers as they weaved their webs. The experiment revealed that spiders rely on a shared set of movements amounting to “a playbook or website building algorithm” to create elegant and geometrically precise structures, even though they have a whole small brain compared to humans.

Co-author Andrew Gordus, behavioral biologist at JHU, said he was inspired to take on the project as he was birding with his son and saw a particularly spectacular spider web. “I was like, ‘If you went to a zoo and saw a chimpanzee building this, you would think he’s an amazing and awesome chimpanzee.’ said Gordus. “Well, it’s even more amazing because a spider’s brain is so small and I was frustrated that we didn’t know more about how this remarkable behavior happens. Now we’ve defined it all. the choreography for creating websites, which has never been done. for any animal architecture at this beautiful resolution. “

Enlarge / An orb weaver spider.

Johns Hopkins University

Besides being aesthetically striking wonders of nature, cobwebs serve as a kind of physical record for many aspects of a spider’s behavior, according to the authors. Gordus and his colleagues believed they could quantify the weaving behavior of orbs, because the process of building a web can be easily defined by both the path of a spider and the geometry of the web.

There are many different species of orb-weaving spiders, but the JHU team chose to work with them. Uloborus diversus. The team chose U. diversus because it stays active all year round and is also conveniently small. The specimens were collected in Half Moon Bay, California, and kept in a greenhouse on campus. There the spiders ate fruit flies once a week. Only adult female spiders have been used, as adult males rarely build webs.

A spider's web seen with night vision.
Enlarge / A spider web seen with night vision.

Johns Hopkins University

For the actual experiments, the team designed a plexiglass arena in the lab, papered around the edges to encourage website creation, and equipped with infrared cameras and infrared lights. (U. diversus is a nocturnal spider, with a preference for building horizontal webs in the dark.) Next, the researchers transferred six spiders to the arena and recorded the spiders each night as they wove their webs for 24 hours in mean.

This activity generally followed a well-defined progression. The spider begins by exploring space before building a protoweb that will not be part of the final structure. Think of an artist producing a preliminary sketch. The protowebs are quite disorganized and there are long irregular pauses in the activity of the spider as it builds its protoweb, sometimes for up to eight hours, because you can’t rush the inspiration.

“This state of web construction is believed to be an exploratory phase during which the spider assesses the structural integrity of its environment and locates the final web anchor points,” the authors wrote.

Then the spider moves on to the construction of the spokes and the frame of the web. “Frame construction is often the result of anchoring the tang to the periphery before the return, then walking outward along an anterior radius, anchoring the tang of the frame to the end of the line, then back to the hub, “the authors wrote.

Use artificial intelligence to follow the construction of the spider web.
Enlarge / Use artificial intelligence to follow the construction of the spider web.

Johns Hopkins University

With the spokes and frame in place, the spider moves on to building an auxiliary spiral, which only takes a few minutes. Scientists believe this step helps stabilize the structure before the spider builds the final capture spiral, as the auxiliary spiral is temporary. The spider usually removes the web once it is complete. Once the capture spiral is complete, the spider crouches at the hub, sometimes for several days, patiently waiting for its prey to become trapped in its web.

Researchers were able to track millions of individual leg movements by designing their own machine vision software for this purpose. “Even if you record it on video, it represents a lot of steps to follow, over a long period of time, for many individuals”, said co-author Abel Corver, a graduate student studying web design and neurophysiology. “It’s just too much to go through each frame and annotate the points of the legs by hand. So we trained machine vision software to detect the spider’s posture frame by frame so that we could document whatever the legs do to create an entire canvas. “

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