The motion of spiders in the web was studied as electrons orbiting the nucleus

Female Trichonephila spider (left) alongside a much smaller male (right). Credit: MPI of Animal Behavior / Alex Jordan

A little golden spider weaving a gold ball faces a big challenge when looking for a partner. She’s a fraction of the size of a massive female, but she has to carefully step into her net and approach her unnoticed because a cannibalistic female will kill and eat her if she makes one wrong move in her net. Adding to this gambling the competition he faces with other men in the sensitive arena of the net as well, you get a complex optimization problem that even human analysts find intimidating. Yet these little spiders hardly have what we would recognize as a brain. So how are they doing? This is a question that has fascinated Alex Jordan and members of his laboratory at the Max Planck Institute of Animal Behavior for more than a decade. Now they are closer to the answer in collaboration with researchers at the Weizmann Institute of Science.

The solution seems to be found in the magnetism of the animal, or more specifically, in the effective physical forces experienced by males and females on the elastic surface of the spider web. “Our original concept was to explore the idea that these spiders moving around the web behave like electrons orbiting a nucleus or planets orbiting stars,” says Jordan, who heads the Integrative Behavioral Ecology Lab at the Max Planck Institute of Animal Behavior. is the second senior author of the study. From this original idea, a research program emerged that led two groups to develop a physical model and conduct experiments in the rainforest of Panama.

Attractive women

Although the details of precise physics eventually differed from both the atomic and cosmic levels, the concept proved useful. “Imagine electrons orbiting a nucleus or a massive star in space so large that it creates its own gravitational field and pulls objects around it – a giant, cannibalistic woman can be thought of in the same way,” Jordan says. “Now imagine smaller planets, satellites or comets approaching this attractive force – these are our little, brave men.” Approach the stars (or the woman) too quickly or from the wrong angle, and you may get caught up in her allure. On a cosmic scale, this leads to a cosmic collision that vaporizes the planet. For a fearless male, the wrong approach means getting into a fatal attraction and being caught.

“While working in the rainforests of Panama, I have seen overzealous males fall victim to cannibalistic females many times, especially when they choose the wrong path or approach the female too quickly,” says Sylvia Garza, another author of the publication. in a study that spent months in Panama as a master’s student and recorded the behavior of male and female spiders and then used machine learning methods to track their every move.

disgusting males

Just as the smaller planets have their own attraction, so do the males – initially approaching a perceived competitor. Males also begin to fight each other as they get closer and closer, causing them to behave much more than the electrons around the nucleus.

“The movement of these males is reminiscent of the interactions between particles that attract or repel each other depending on the distance between them,” says Amir Haluts, a physicist by training and lead author of research at the Weizmann Institute of Science. Another senior author, Nir Gov, who is also from Weizmann, says, “We use models to map the effective physical forces that men experience, allowing us to explain their movements online and compete for the dynamics of males of different sizes.” When the males orbit each other, they end up getting too close to each other and colliding in an open battle. All of this is played on a network surface that acts as a channel for the vibration a man uses to communicate, but which can also warn the female of his presence and lead to a fatal attack.

The group’s research shows that the seemingly complex decisions men make that balance risk and reward, life and death, do not require advanced intelligence or an understanding of the game they are playing. Instead, the same solutions can be achieved by recognizing vibrations in the network and reacting to physical tensile and repulsive forces, just as physical particles can do. “Early on, I was amazed at our first results, which showed that these males were able to solve these complex tasks apparently without the required cognitive machinery,” Jordan says. “I joked with Niri that it’s almost like these males are electrons orbiting a female ‘core.’


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More information:
Amir Haluts et al, The spatiotemporal dynamics of animal competitions arise from the effective forces between competitors, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073 / pnas.2106269118

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