Like Planets Orbiting a Star, Male Spiders are attracted to Females

When it comes to finding a partner, the little male golden orb-weaving spider faces a significant barrier. The golden orb spider, also known as the banded-legged nephilia, is an arachnid belonging to the nephila genus. Nephila spiders, sometimes known as golden orb-weavers, huge wood spiders, or banana spiders, are found all over the world.

The male spider is a sliver of the gigantic female’s size, but he must enter her web carefully and approach her without being seen, for the cannibalistic female will murder and consume him if he makes one false move on her web.

When you combine this risk with the fact that he is competing against other guys in the delicate realm of the internet, you have a complex optimization problem that even human analysts would find difficult to solve. These little spiders, on the other hand, barely have what we would call a brain.

So, how do they make it work? For more than a decade, Alex Jordan and his colleagues at the Max Planck Institute of Animal Behavior have been fascinated by this subject.

They’re getting closer to an answer now that they’ve teamed up with Weizmann Institute of Science experts. The answer appears to be found in animal magnetism, or more precisely, in the effective physical forces that males and females encounter on the spider web’s elastic surface.

Golden orb-weaving spider

Because of the color of its silk, the golden orb spider gets its name. This color is said to serve two purposes: in the sun, it attracts bees drawn to the brilliant yellow, while in the shade, it blends in with the foliage, enticing other insects.

“Our initial concept was to explore the idea that these spiders moving on the web behave like electrons orbiting a nucleus, or planets orbiting a star,” says Jordan, who leads the Integrative Behavioral Ecology Lab at the Max Planck Institute of Animal Behavior, and is co-senior author on the study.

A study program was born from this original notion, leading the two teams to create a physical model and conduct trials in the Panamanian rainforest.

Competitive web arena

While the exact physics of both the atomic and cosmic levels eventually differed, the concept proved beneficial.

Working in the rainforests of Panama, I’ve seen over-zealous males fall victim to the cannibalistic females many times, especially when they take the wrong path, or approach the female too fast.

Sylvia Garza

“Imagine electrons orbiting a nucleus, or a massive star in space, so large that it generates its own gravitational field pulling in objects around it the giant, cannibalistic female can be thought of in the same way,” says Jordan. “Now imagine smaller planets, satellites, or comets coming near this attractive force these are our tiny, brave males.”

If you approach the star (or female) too quickly or from an improper perspective, you risk being sucked by her seductive draw. On a cosmic scale, this will result in planetary vaporization due to a cosmic collision. An improper approach will result in the intrepid male succumbing to a fatal attraction and becoming prey.

“Working in the rainforests of Panama, I’ve seen over-zealous males fall victim to the cannibalistic females many times, especially when they take the wrong path, or approach the female too fast,” says Sylvia Garza, co-author of the study, who spent months in Panama as a Master’s student recording the behavior of male and female spiders, then using machine-learning approaches to track their every movement.

The abdomen of a female golden orb spider can be up to 30mm long. In both height and weight, she dwarfs the small 5mm male. After mating, practically all nephila species put the male at danger of being devoured by the female.

To avoid being eaten, the male will approach the female when she is already eating or present her with a food bundle. The male will fertilize the female while she is preoccupied and then retreat to a safe distance.

Vibratory cues

Males are attracted to one another in the same way as smaller planets are attracted to one another when approaching a perceived rival. As they approach closer, the guys begin to resist each other, behaving much like electrons surrounding a nucleus.

“The motion of these males resembles interactions between particles that attract or repel one another depending on the distance between them,” says Amir Haluts, a physicist by training and lead author of the study from the Weizmann Institute of Science.

Co-senior author Nir Gov, also from the Weizmann, says: “We use models to map the effective physical forces that males experience, allowing us to explain their motion on the web, as well as contest dynamics of males of different sizes.”

The guys will finally approach too close together as they orbit one another, slamming into each other in open combat. All of this takes place on the web’s surface, which serves as a conduit for the vibrations used by males to communicate, but can also alert females to their presence, leading to a lethal attack.

Males’ seemingly complex judgments, balancing risk and reward, life and death, do not necessitate sophisticated intelligence or awareness of the game they are playing, according to the team’s findings.

Instead, the same solutions can be achieved by sensing vibrations on the web and responding to the physical forces of attraction and repulsion, just as physical particles might do.

“Early on, I was perplexed by our first results, which showed that these males could solve these complex tasks apparently without the required cognitive machinery,” says Jordan.

“I joked with Nir that it’s almost like these males are electrons orbiting around the female ‘nucleus’. This led to us coining the term ‘Atomic Spiders’ and it turns out that it may not be that far from the truth.”