The Precise Choreography of Nature’s Master Weavers

A hackled orb weaver rests on its web. Gordus and his team used these animals as model organisms to study the construction of spider webs.

Image Courtesy of Flickr.

In one act of the famous ballet “Swan Lake,” fourteen dancers raise their arms and flutter their hands in synchrony, while the lead ballerina spins in a slow pirouette center-stage. As the ballet progresses, the dancers execute a series of choreographed motions—jumps, twirls, and leaps—that are distinctive for each of the four acts in the performance.

The sequence of a ballerina’s movements can be applied to the equally elegant and complex process of spider web-building. Andrew Gordus, an assistant professor and behavioral biologist at John Hopkins University, has studied spider web construction for over five years. He explained that spiders, like ballerinas, build up a repertoire of techniques, such as leg sweeping, abdomen bending, and silk pulling, which they use during specific phases of web-building. When combined, these movements form the intricate architecture of their web.

Gordus’s fascination with web-building began over five years ago, when he stumbled upon a stunning web while walking through Central Park. At the time, he wondered how such a small organism could accomplish such a complex feat.

“It’s amazing that an animal with a brain no bigger than a fly’s built this web,” Gordus said. “And it’s really impressive because if you went to a zoo, and you saw a chimpanzee build this web, you would think, ’Well, that’s a really talented chimpanzee.’ But this is being done by an animal with a really tiny brain.”

This discovery prompted Gordus to read all of the existing scientific literature on web construction and to email researchers studying spider behavior. However, the field was not well-developed, and some of his questions remained unanswered.

In his last few months as a postdoc at Rockefeller University, Gordus’s advisor allowed him to conduct experiments on spiders in a separate facility on their campus in New York City. When Gordus moved to Johns Hopkins University in 2016 to start his own lab, he continued studying web-building as a side project. Over time, more graduate students joined his lab, and the project gained traction, becoming the largest undertaking in his laboratory.

Though Gordus is fascinated by the physical web itself, he is more interested in the behavioral processes that govern its construction. In his 2021 study published in Current Biology, Gordus studied the movements of hackled orb weavers, which are found in the western United States. Orb weavers typically build spiral-shaped webs using strands of silk that have the same dry, wooly texture as cotton candy. Gordus’s love for these creatures is evident—a red spider was sewn onto the black jacket he was wearing during our interview. (His hat was also emblazoned with a cartoon worm—the other model organism he primarily works with in his lab is the roundworm, C. elegans.)

In his study, Gordus and his team were interested in inferring the spiders’ internal states by examining the construction of their webs. He explained that every animal’s behavior is dictated by a myriad of internal states, including hunger, sexual arousal, and emotion, that manifest in physical actions, such as grooming or mating rituals. “The question we wanted to know was: What are the behaviors that this web is a record of?” Gordus said. “What are the behaviors, the rules, [for each stage of] web-building?”

In order to study these spiders’ movements, Gordus and his team used infrared illumination and a high-speed camera, which captured the minute motions of each of the spider’s eight legs. The entire process involved several attempts, unexpected failures, and an abundance of perseverance. Gordus said that they originally tried to study the spiders under red light, but the orb weavers refused to build their webs without complete darkness. The team then transitioned to infrared light, which is invisible to both humans and spiders.

Furthermore, to track the orb weavers’ movements, the scientists placed labels with infrared dyes on each of the spiders’ legs, a technique commonly used to examine fly behavior. However, they were met with great resistance. “[The spiders] hated having their limbs labeled, and they would just spend the whole time sitting there trying to take it off,” Gordus said. “And then, they would [sometimes stop building and would] stick to their own web, and we would come back, and they would just be dangling.”

Instead of the labels, the team decided to use a camera that detected the reflection of infrared light off of the spiders’ bodies. They also adopted two recently published algorithms specifically designed for limb tracking, called LEAP and DeepLab Cut. The scientists first trained the algorithms on several thousand frames of spider movements, which they manually tracked. The algorithms were then able to track millions upon millions of frames, capturing the minute motions of the spiders’ legs.

After monitoring six different orb weavers, the team adopted a machine learning algorithm, called the hierarchical hidden Markov model (HHMM), to deduce patterns in web construction. The algorithm employed probability models to predict the spider’s web-stage based on transitions in its behavior, without knowing where the spider was on the web. The researchers found that the predictions made by the HHMM mapped onto established phases of web-building based on the spider’s position. This solidified the association between the orb weaver’s distinct behaviors and specific phases of construction. Developing the model involved trial and error—existing algorithms used to predict fly movements did not perform as well when applied to orb weavers, so they had to write their own code from scratch.

After years of troubleshooting and diligent work, Gordus’s lab finally developed a fully-fledged experimental system. Upon collecting their data and analyzing the results, the researchers came to a startling revelation. Contrary to their expectations, the orb weavers did not build their webs reflexively, moving from phase to phase without pausing. Instead, the spiders revised their work as they went, returning to past locations on their webs to rearrange misplaced strands of silk. Sometimes, the weavers even repeated entire phases of web construction before proceeding again, indicating that they might have internal models of their webs that they are attempting to replicate.

“We were surprised [at] how frequently the spider could go back and try a prior phase over again,” Gordus said. “[The spiders are] constantly assessing what they’re building with this internal goal, and [they have] a flexible way of trying to get to that goal.”

Looking ahead, Gordus’s team hopes to study the effects of certain drugs on web construction in order to elucidate the neurological activity associated with each phase of building. The team is looking into the effects of two chemicals in particular: lysergic acid diethylamide (LSD), a potent psychedelic drug, and ecdysone, a steroidal hormone in arthropods that induces molting and influences decision making.

Already, the researchers have confirmed that ecdysone causes the orb weavers to stop building their webs at a certain stage. They also know that giving the spiders a microdose of LSD results in the construction of perfectly symmetrical, evenly-spaced webs. Gordus said he is interested in further studying the effects of LSD on neuromodulatory pathways, or chemical pathways in the brain that control internal states.

“If the spiders build really good webs [after consuming LSD], then we want to know what changed in their behavior,” Gordus said. “Are they just executing the behaviors really well, like a professional web builder? Or do they have [obsessive compulsive disorder], and they’re constantly doing a lot of error correction? We’d like to know, what is the behavioral readout?”

By deducing which motor neurons are activated in the spiders’ brains after the administration of certain drugs, the researchers might be able to understand the effects of these chemicals on human behavior. For now, though, Gordus and his team are focused on studying orb weavers and the graceful, intricate choreography of their web-building.